Hydrology of Major Estuaries And Sounds of North Carolina

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United States Geological Survey Water-Supply Paper 2221

Prepared in cooperation with the North Carolina Department of Natural Resources and Community Development

COVER: Harbor at Wanchese, North Carolina, drawmg by Ltbby Gtese from copynghted photograph by Btll Patterson (by permtsswn of Braxton Flye, edttor. North Carohna Coastal Ftshmg and Vacatwn Gutde)

Hydrology of Major Estuaries And Sounds of North Carolina

By G. L. GIESE, H. B. WILDER, and G. G. PARKER, JR.

Prepared m cooperat1on w1th the North Carohna Department of Natural Resources and Commumty Development

U.S. GEOLOGICAL SURVEY WATER-SUPPLY PAPER 2221

DEPARTMENT OF THE INTERIOR

DONALD PAUL HODEL, Secretary

U.S. GEOLOGICAL SURVEY

Dallas L. Peck, Director

UNITED STATES GOVERNMENT PRINTING OFFICE 1985

For sale by the Distribution Branch, U.S. Geologtcal Survey, 604 South Pickett Street, Alexandrta, VA 22.304

L1brary of Congress Catalogmg m Pubhcatlon Data

G1ese, G L Hydrology of maJor estuanes and sounds of North

Carolma (U S Geolog1cal Survey water-supply paper , 2221) Bibliography p 105 Supt of Docs no I 19 13 2221 1 Estuanes-North Carolma 2 Sounds Geomorphology­

North Carolma 3 Hydrology-North Carolma I Wilder, Hugh B II Parker, G G Ill North Carolma Dept of Natural Resources and Commumty Develop­ment IV T1tle V Serres Geolog1cal Survey water­supply paper , 2221

GC97 G54 1985 551 46'48 85--600158

CONTENTS

Abstract 1 IntroductiOn 1 I General hydrology 2

Ocean tides 4 Estuanne flow 6 Sahmty 7 Estuanne types 9

Highly stratified estuary 9 Partially mixed estuary 9 Well mixed estuary 11

Sediment 11 Effects of wmds and hurricanes 15 The salt-marsh environment 16

2 Hydrology of the Cape Fear River estuanne system 19 The Cape Fear River estuary 19

Flow 20 Freshwater mflow 20 Tide-affected flow 21

Water quahty 22 Sediment 25 Sahmty 26

Vanat10ns m time and space 26 RelatiOn of sahmty to freshwater mflow and tides 29

The Northeast Cape Fear River estuary 31 Freshwater mflow 31 Tide-affected flow 32 Water quahty 35 Sediment 35 Sahmty 37

Vanations m time and space 37 Relation of sahmty to freshwater mflow 39

3 Hydrology of the Pamhco Sound estuanne system 40 Pamhco Sound 41

Water budget and flow 41 Water levels 48 Water quahty 48 Sahmty 53

The Neuse-Trent River system 56 Effects of wmd on water levels and specific conductance 56 Water quahty 57 Spatial vanat10ns m sahmty 58 Frequency of saltwater mtrus10n 60 Relation of sahmty to freshwater mflow 63

The Tar-Pamhco River system 63 Water levels 68 Flow 70

Contents Ill

3 Hydrology of the Pamhco Sound estuanne system- Contmued The Tar-Pamhco Rtver system- Contmued

Water quahty 71 Sedtment 71 Sahmty 75

4 Hydrology of the Albemarle Sound estuarme system 79 Albemarle Sound and vtctmty 79

Water levels ,80 Freshwater mflow 81 Extent and duratiOn of saltwater mtruswn 85

The Chowan Rtver estuary 86 Water levels 91 Flow 91 Water quahty 96 Sahmty 97

The Roanoke Rtver estuary 1 00 Flow 100 Water quality 102

Summary and dtscusswn 1 04 Selected references 1 05 Metnc conversion factors 1 08

PLATE

Map showmg maJor estuanes and sounds of North Carohna (In pocket)

FIGURES

A Map showmg dramage network of eastern North Carohna and approximate extent of estuanes and sounds 3

I 1-1 3 Graphs showmg I I Tide curve for Cape Fear River estuary at Wllmmgton

for August 9-22, 1977 5 I 2 DiUrnal mequahties produced from mteractwn of

semidlllrnal and diUrnal tidal components 5 I 3 Tide curves at spnng tide and neap tide 5

I 4 Sketch showmg behavwr of an Idealized tide wave man estuary 6 I 5 Graph showmg relatwn between specific conductance and

chlonde concentratiOns m North Carohna estuanes 8 I 6-1 9 Sketches showmg

IV Contents

I 6 A Net circulatiOn patterns m a highly stratified estuary 10

B Sahmty profile through section X-X' t10 C Net velocity profile through sectwn X-X' 10

I 7 A Net circulatiOn patterns m a partially mtxed estuary 12 B Chlonde concentratiOn profile through section Y-Y' 12 C Net velocity profile through sectwn Y-Y' 12

l 8 A Net circulatwn patterns m a well mixed estuary 13 B Chlonde concentration profile through section Z-Z' 13 C Velocity profiles through sectwn Z-Z' 13

I 9 The effect of forward motion of a hurncane on wmd velocities m each quadrant 17

2 I Graph showmg concurrent discharge relatiOn for estimatmg runoff from the ungaged dramage area between the mdex statiOns and the mouth of the Cape Fear River estuary 21

2 2 Graph showmg magmtude and frequency of annual mmimum 7-day average net flow of the Cape Fear River estuary at the mouth, near Southport 22

2 3 Map showmg Cape Fear River estuary upstream from WIImmgton 23 2 4-2 II Graphs showmg

2 4 Stage and discharge of the Cape Fear RIver estuary near Phoemx on March 8, 1967 25

2 5 Vanatwn of velocity With depth of the Cape Fear River estuary at Navassa on May 13, 1966 25

2 6 Longitudmal vanations m chlonde concentratiOns of the Cape Fear River estuary at high-slack water, November I, 1967 26

2 7 Vanatwns m chlonde concentratiOns m a cross sectiOn of the Cape Fear River estuary I 5 miles upstream from Market Street, W Ilmmgton, on June 5, 1962 27

2 8 RelatiOn between chlonde concentratiOn and specific conductance at a known pomt m the Cape Fear River estuary and chlonde concentration and specific conductance at other pomts either upstream or downstream 27

2 9 RelatiOn between chlonde concentratiOn near the bottom of the Cape Fear River estuary upstream from Wilmmgton at high slack water and the number of hours the chlonde concentratiOn will exceed 200 mgj L 28

2 I 0 M agnttude and frequency of highest annual tide m the Cape Fear River estuary at Wilmmgton, corrected for component of nver stage due to freshwater mflow 29

2 II I nterrelatwns of maximum encroachment of 200 mgj L chlonde, outflow at the mouth, and tide heights m the Cape Fear River estuary 30

2 12 Map showmg Northeast Cape Fear River estuary 31 213-216 Graphsshowmg

2 13 RelatiOn between flow measured at Northeast Cape Fear River at Chmquapm and net outflow from the Northeast Cape Fear River estuary at the mouth 32

2 14 Low-flow frequency curves for the Northeast Cape Fear estuary 33

2 15 Stage and discharge as measured contmuously dunng October 23, 1969, m theN ortheast Cape Fear River estuary, 6 4 miles upstream from the mouth 34

2 16 Average flushmg time for a solute InJected mto the Northeast Cape Fear River estuary about 6 5 miles upstream from the mouth 35

2 17 Sketch showmg longitudmal vanatwns m specific conductance of the Northeast Cape Fear River estuary on November 9, 1966 37

2 18-2 20 Graphs showmg 2 18 Specific conductance type curve for theN ortheast Cape

Fear River estuary 38 2 19 RelatiOn of the locatiOn of the saltwater front m the

Northeast Cape Fear RIver estuary to the precedmg 21-day average discharge at Chmquapm 39

2 20 Frequency of mtruswn of 200 mgj L chlonde for vanous locatiOns m the Northeast Cape Fear RIver estuary 40

Contents V

3 1-3 4 Maps showmg 3 I Depth of Pamhco Sound 42 3 2 Texture of bottom sediments m Pamhco Sound 42 3 3 Oxidizable organic matter and organic carbon content of

bottom sediments m Pamhco Sound 43 3 4 CalciUm carbonate content of bottom sediments m Pamhco

Sound 43 3 5, 3 6 Graphs showmg

3 5 Magnitude and frequency of annual minimum 7- and 30-consecuttve-day average mflow to Pamhco Sound from dtrect and mdtrect land dramage 45

3 6 Magnitude and frequency of annual maximum 7- and 30-consecuttve-day average mflow to Pamhco Sound from dtrect and mdtrect land dramage 46

3 7 Schematic drawmg showmg estimated water levels m Pamhco Sound at 0200 and 0500 hours on September 12, 1960, dunng H urncane Donna 49

3 8 Map showmg areas subJect to flood mundatwn caused by wmd tides havmg A, 50 percent chance of bemg equaled or exceeded m any one year and B. I percent chance of bemg equaled or exceeded m any one year 50

3 9 Map showmg sampling statiOns used m Pamhco Sound study by Woods ( 1967) 51

3 I 0 Graphs showmg A, Mean monthly water surface temperature of Pamhco Sound and B. Relation between water surface temperature of Pamhco Sound and air temperature at Hatteras 52

3 II Map showmg average surface o;;ahnity of water m Pamhco Sound and VICinity for the month of Apnl 54

3 12 Map showmg average surface salinity of water m Pamhco Sound and VICinity for the month of December 55

3 13 W md diagram for the Neuse R 1ver estuary at New Bern 56 3 14-3 16 Graphs showmg

3 14 Change m water level of the Neuse River estuary at New Bern due to wmd as recorded at New Bern Airport 57

3 15 Effect of wmd on water levels and bottom specific conductance m the Neuse River estuary at New Bern, January 22-30, 1965 58

3 16 Range of water temperatures m Neuse R 1ver estuary at New Bern from October 1963 through August 1967 60

3 17 Map showmg hnes of equal specific conductance for the Neuse Rtver estuary, August 13, 1967 61

3 18-3 27 Graphs showmg

VI Contents

3 18 Change m surface specific conductance With upstream and downstream distance m theN euse and Trent estuanes 62

3 19 Percentage of time specific conductances equaled or exceeded mdicated values m the Neuse River estuary at New Bern, 1957-67 62

3 20 Percentage oft I me surface specific conductances were equaled or exceeded for severallocatwns m the Neuse Rtver estuary, 1957-67 62

3 21 Percentage of time mtegrated specific conductances were equaled or exceeded for several locatiOns m the Trent RIver estuary, 1959-61 62

3 22 Percentage of time surface and bottom salinities were equaled

or exceeded m the Neuse R1ver estuary at Garbacon Shoals Light, 1948-68 64

3 23 Percentage of time surface and bottom salimt1es were equaled or exceeded m the Neuse R1ver estuary at Wilkmson Pomt L1ght, 1958-67 65

3 24 Percentage of time surface and bottom salimt1es were equaled or exceeded m the Neuse R1ver estuary at Hampton Shoals L1ght, 1958-60 66

3 25 Percentage of time surface and bottom salimt1es were equaled or exceeded m the Neuse River estuary at Fort Pomt L1ght, 1958-67 67

3 26 Percentage of time a specific conductance of 800 JJmhos will be equaled or exceeded m the Neuse R1ver at New Bern for vanous annual average discharges at K mston 68

3 27 Percentage of time a specific conductance of 800 JJmhos will be equaled or exceeded m the Trent R1ver near New Bern for vanous annual average discharges at Trenton 68

3 28 Wmd diagram for the Pamlico River estuary 69

3 29-3 39 Graphs showmg 3 29 Water levels m the Pamhco R1ver at Washmgton and effective

component of wmd speed at Cape Hatteras 69 3 30 RelatiOn of nse m water level m the Pamlico R1ver at

Washmgton to effective wmd velocity 70 3 31 Frequency curve of annual mean discharge of Tar River at

Tarboro 71 3 32 Low-flow frequency curves of annual lowest mean discharge

for mdicated number of consecutive days for Tar River at Tarboro 72

3 33 Maximum 7- and 30-consecutive-day average discharges of the Tar River at Tarboro 74

3 34 Average monthly temperature of Pamlico R 1ver at Washmgton 74

3 35 Sediment-transport curve for the Tar River at Tarboro 75 3 36 Cumulative frequency curves of specific conductance and

chlonde, Pamhco River at Washmgton 75 3 37 RelatiOn between surface specific conductance at one pomt m

the Pamhco R 1ver estuary and surface specific conductance at other pomts either upstream or downstream 76

3 38 Percentage of time a specific conductance of 800 JJmhos will be equaled or exceeded m the Pamhco River at Washmgton for vanous annual average discharges at Tarboro 77

3 39 Relation between the precedmg 30-day average discharge of the Tar River at Tarboro and the locatiOn of the saltwater front 78

4 I Depth, m feet, of Albemarle Sound 80 4 2 Texture of bottom sediments m Albemarle Sound 81

4 3-4 5 Graphs showmg 4 3 Wmd speed at Elizabeth C1ty and water levels at Chowan

River near Edenhouse, Albemarle Sound near Edenton, and Pasquotank River at Elizabeth City. July 27-30 and November 29-December 3. 1960 81

4 4 M mimum 7- and 30-consecutive-day average mtlow to Albemarle Sound from land dramage 83

4 5 Maximum 7- and 30-consecutive-day average mtlow to Albemarle Sound from land dramage 85

Contents VII

4 6 Map showmg average surface sahmty of water m Albemarle Sound and vtctmty durmg the month of March 86

4 7 Map showmg average surface sahmty of water m Albemarle Sound and vtctmty dunng the month of December 87

4 8--4 15 Graphs showmg 4 8 Average monthly spectftc conductance of Albemarle Sound

near Edenton, 1957-67 89 4 9 Cumulative frequency curve of spectftc conductance and

chlonde, Pasquotank Rtver near Elizabeth Ctty 89 4 10 Cumulattve frequency curves of spectftc conductance and

chlonde, Pasquotank Rtver at Elizabeth Ctty 89 4 11 Cumulattve frequency curve of spectftc conductance and

chlonde, Perqmmans Rtver at Hertford 90 4 12 Cumulattve frequency curves of spectftc conductance and

chlonde, Chowan Rtver near Edenhouse 90 4 13 Cumulattve frequency curves of spectftc conductance and

chlonde, Albemarle Sound near Edenton 90 4 14 Cumulative frequency curve of spectftc conductance and

chlonde, Scuppernong Rtver near Cresswell 90 4 15 Cumulative frequency curve of spectftc conductance and

chlonde, Scuppernong Rtver at Columbta 91 4 16 Map showmg Chowan Rtver, maJor tnbutanes, and adJotnmg

swampland 92 4 17--4 23 Graphs showmg

VIII Contents

4 17 Contmuous water-level records for Chowan Rtver near Eure and Chowan Rtver near Edenhouse for December 6-12, 1974 93

4 18 Contmuous water-level records for ftve gagmg statwns on the Chowan Rtver for December 6, 1974 94

4 19 Monthly average stages for Chowan Rtver near Eure and Chowan R tver near Eden house 95

4 20 Frequency curve of annual mean dtscharges, combmatwn of Blackwater Rtver at Franklin, Ya , and Nottoway R tver near Sebrell, Ya 95

4 21 low-flow frequency curves of annual lowest mean dtscharge for mdtcated number of consecutive days, combmatwn of Blackwater R tver at Franklin, Ya , and Nottoway RIver at Sebrell, Ya 96

4 22 Monthly average discharge and maxtmum and mmimum daily average discharge of Chowan River near Eure and Chowan RIver near Eden house 97

4 23 Percentage of time bottom specific conductances exceeded 800 micromhos for vanous annual average discharges for Chowan River at Edenhouse, 1958-67 99

4 24 Map showmg distnbutary system of the lower Roanoke River 101 4 25 Frequency curve of annual mean dtscharges of Roanoke Rtver

at Roanoke Rapids 102 4 26 low-flow frequency curves of annual lowest mean discharge for

mdtcated number of consecuttve days, for Roanoke River at Roanoke Rapids 102

TABLES

I I The ten most Important partial tides 4 I 2 Pnmary production rates of vanous ecosystems 18 2 I Summary of chemical analyses of freshwater samples collected at key

stations m the Cape Fear River basm 24 2 2 Summary of chemical analyses of freshwater samples collected at key

stations m the Northeast Cape Fear River basm 36 3 I Monthly and annual gross water budget for Pamhco Sound 44 3 2 Tidal flow and related data for Oregon, Hatteras, and Ocracoke Inlets 47 3 3 Predicted tide ranges and maximum currents for locations at or near

mlets to Pamhco Sound 47 3 4 Summary of chemical analyses of freshwater samples collected at key

statiOns m the Neuse-Trent River system 59 3 5 Summary of chemical analyses of freshwater sample~ collected at key

stations m the Tar-Pamhco River basm 73 4 I Relative effects of wmd on vertical movement of water levels at selected

locatiOns m and near Albemarle Sound 82 4 2 Monthly and annual gross water budget for Albemarle Sound 84 4 3 Maximum chlonde concentrations and specific conductance of water

at daily sampling stations m the Albemarle Sound estuanne system 88 4 4 Summary of chemical analyses of freshwater sample~ collected at key

stations m the Chow an RIver basm 98 4 5 Summary of chemical analyses of freshwater sample~ collected at key

stations m the Roanoke River basm 103

Contents IX

Hydrology of Major Estuaries and Sounds of North Carolina

By G. L. Giese, H. B. Wilder, and G. G. Parker, Jr.

Abstract

Hydrology-related problems assoCiated w1th North Carolma's maJor estuanes and sounds mclude contami­nation of some estuanes w1th mumCipal and mdustnal wastes and dramage from adJacent, mtens1vely farmed areas, and nu1sance-level algal blooms In add1t1on, there 1s excess1ve shoalmg m some nav1gat1on channels, salt­water mtrus1on mto usually fresh estuanne reaches, too­high or too-low salm1t1es m nursery areas for vanous es­tuanne spec1es, and flood damage due to hurncanes

The Cape Fear R1ver 1s the only maJor North Carolma estuary havmg a d1rect connection to the sea Short-term flow throughout most of 1ts length 1s domi­nated by ocean t1des The estuanne reaches of the Neuse-Trent, Tar-Pamllco, Chowan, and Roanoke R1ver systems are at least partly sh1elded form the effects of ocean t1des by the Outer Banks and the broad expanses of Pamllco and Albemarle Sounds W1th the probable ex­ception of the Roanoke R1ver, wmds are usually the do­mmant short-term current-producmg force m these es­tuanes and m most of Pamllco and Albemarle Sounds

Freshwater entermg the maJor estuanes 1s, where not contammated, of acceptable quality for dnnkmg w1th m1mmum treatment However, 1ron concentrations m ex­cess of 0 3 m1lllgrams per liter somet1mes occur and water drammg from swampy areas along the Coastal Plam 1s often h1ghly colored, but these problems may be remed1ed w1th proper treatment Nu1sance-Jevel algal blooms have been a recurrmg problem on the lower es­tuanne reaches of the Neuse, Tar-Pamllco, and Chowan R1vers where nutnents (compounds of phosphorous and mtrogen) are abundant The most destructive blooms tend to occur m the summer months durmg penods of low freshwater discharge and relatively h1gh water tem­peratures

Saltwater mtrus1on occurs from t1me to t1me m all maJor estuanes except the Roanoke R1ver, where releases from Roanoke Rap1ds lake and other reservo1rs dunng otherw1se low-flow penods effectively block salme water from the estuary Sallmty strat1f1cat1on 1s common m the Cape Fear and Northeast Cape Fear R1vers, but IS less com­mon m other estuanes wh1ch do not have d1rect oceamc connections and where wmd 1s usually effective m vert1cal m1xmg The greatest known upstream advance of the salt-

water front (200 m1lllgrams per liter chlonde) m most North Carolina estuanes occurred durmg or m the aftermath of the passage of Hurncane Hazel on October 15, 1954 Hur­ncane Hazel ended an extreme drought when many North Carolina nvers were at or near mm1mum recorded flows Consequently, saltwater mtrus1ons m many North Carolina estuanes were at or near the max1mums ever known to have occurred When the hurncane struck, h1gh storm t1des along the coast drove saline water even further up­stream m many Jocallt1es The probability of two such rare events happenmg concurrently 1s not known, but the re­currence mterval may be reckoned m hundreds of years

New shoalmg matenals found m the lower chan­nelized reaches of the Cape Fear and Northeast Cape Fear R1vers are pnmanly denved, not from upstream sources, but from nearby shore eros1on, from slumpmg of matenal adJacent to the dredged channels, from old sp01l areas, or from ocean-denved sed1ments earned upstream by near­bottom dens1ty currents It 1s not known at th1s t1me whether th1s holds true for other estuanes d1scussed m th1s report

INTRODUCTION

The estuaries and sounds of North Carolina are among the State's most valuable resources They serve as routes for low cost transportation by means of ships and barges, as sources of large amounts of water for mdustnal and, where not too salty, for mumcipal use They also serve as both fishenes and nursenes for a wide variety of a marme life and as focal pomts for recreational actiVIties Planmng for optimum use of the estuaries for these some­times conflictmg uses depends m part on havmg detailed know ledge of the physical and chemical processes at work m them Problems which have ansen m connectiOn with the uses of North Carolina estuanes and sounds mclude ( 1) contammatmn of some estuaries with mumcipal and mdustnal wastes and dramage from adJacent mtensively farmed areas, (2) excessive shoaling m some navigatiOn channels, (3) m nursery areas, too-high salimties due to low freshwater mflow or too-low salimties due to high freshwater mflow, ( 4) occasional fish kills related to con­tammation or deoxygenatiOn of estuarme waters, (5) nUt-

Introduction

sance-level algal blooms m some estuanes, and (6) flood damage from unusually htgh hurncane-mduced tides

The approximate extent of North Carohna's sounds and estuartes ts shown m figure A, and plate 1 sum­manzes condttions of maxtmum upstream saltwater en­croachment and ttde effects for maJor estuartes These es­tuartes are m an area whtch many feel ts expenencmg the leadmg edge of a wave of agncultural, commerctal, and recreatiOnal development To mmtmtze posstble adverse effects of development and maxtmtze benefits, manage-ment dectstons related to development should be predi­cated, at least m part, on a baste understandmg of the pre­sent hydrology of North Carohna's estuanne waters Often, thts mformat10n has been lackmg or mconvement to gather when dectstons must be made The purpose of thts report ts to summanze current baste knowledge of the hydrology of the maJor estuartes and sounds m North Carohna, not only for use m management dectstons now, but also for use as a general mformat10n source for future estuanne studtes m hydrology and related fields

Thts report was prepared by the U S Geologtcal Survey m cooperation wtth the North Carohna Department of Natural Resources and Commumty Development and ts based partly on data and mterprettve reports ongmatmg from the Geologtcal Survey and partly on data and mter­prettve reports ongmatmg from other Federal, State, local, and pnvate sources These sources are acknowledged m the text where appropnate

Thts summary report, whtle fatrly complete wtth re­spect to work done by the Geologtcal Survey, ts much less so for work done by pnvate and other pubhc agenctes To summartze the vast accumulated body of hydrology-re­lated work done by others IS beyond the scope of thts re­port Rather, the mtent here ts to present a baste ptcture of the hydrology of the maJor estuanes and sounds of North Carohna m terms of freshwater mflow, ttde-affected flow, water levels, freshwater quahty, sahmty, and sedtmentattOn-utthzmg Geologtcal Survey data where avatlable, but ftlhng gaps where posstble wtth mformat10n from other agenctes

Thts report ts dtvtded mto four chapters The first, "General Hydrology," ts pnmartly a dtscusston of baste hydrologtc pnnctples relatmg to ttdes, ttdal flow, sahmty, sedtmentattOn, and the effects of wmds and hurrtcanes The other three chapters summanze present knowledge of the hydrology of mdtvtdual sounds and estuanes m each of three estuarme systems The estuarme systems are, m order of dtscusston, the Cape Fear Rtver system, the Pam­hco Sound system, and the Albemarle Sound system The comprehensiveness of the summanes for each sound or es­tuary ts dtrectly related to the avatlabthty of mformatton on whtch the summanes are based The Cape Fear Rtver estuary, for example, has been much more thoroughly studted than the Roanoke Rtver In general, the larger the estuary, the more complete ts the mformat10n avatlable

2 Hydrology of MaJOr Estuar1es and Sounds of North Carohna

The Cape Fear Rtver estuanne system mcludes the Cape Fear Rtver estuary and the Northeast Cape Fear Rtver estuary These are umque among maJor North Carohna estuaries m that they have a dtrect connectiOn wtth the ocean

The Pamhco Sound estuarme system compnses Pamhco Sound, the Neuse Rtver estuary, the Trent Rtver estuary, the Pamhco River estuary, and a number of lesser estuanes which enter Pamhco Sound These are character­Ized by large channels, small lunar ttdes, and flow whtch IS greatly affected by wmds

The Albemarle Sound system compnses Albemarle Sound, Cumtuck Sound, and those estuartes drammg mto Albemarle Sound, the largest of whtch are the Roanoke Rtver and the Chowan Rtver estuanes These are also charactenzed by small lunar tides and, wtth the posstble exception of the Roanoke Estuary, by the fact that wmd exerts a dommant short-term mfluence on water levels and water movement

1. General Hydrology

A sound IS formally defmed as a relattvely narrow passage of water, too wide and extensive to be called a strait, that connects two water bodies, or It can be a chan­nel passmg between a mamland and an ISland A sound IS also sometimes thought of as m mlet, arm, or recessed portion of the sea Thts last defimt10n comes closest to de­scnbmg Pamhco and Albemarle Sounds, but even It Is not entuely satisfactory Thus, tt may be that the term "sound" as apphed to North Carolma's sounds IS a mis­nomer, but no more formally correct term ts available The term "estuary," as used m this report, IS that part of the lower course of a coastal nver affected by ocean tides

Flow of water m an estuary can be descnbed as the superposition of tidal flow on the otherwise unaffected freshwater discharge of the estuary In the lower reaches of an estuary, average flow due to tides may be many times the flow due to freshwater mflow However, flow due to tides ts cychc and m the North Carohna area ts semidmmal, changmg direct ton every 6 hours, 12 mm­utes, and 30 seconds (6 21 hrs) Over a number of tidal cycles, the flow component from ttdes averages out to be practically zero, whereas the flow component from fresh­water mflow, although It may be smaller, always acts m a downstream dtrection and controls long-term average flow m an estuary

Sahne or salty water m an estuary moves upstream and downstream m response to tidal actiOn, freshwater outflow, and turbulent mixmg In discussmg this move­ment, It IS convement to select an arbttrary value of salin­Ity, the locatton of whtch represents the upstream hmit of the zone of saltwater mtxmg, which we Will refer to as the

v R G N A

0

Lookout

i \

Cope Fear

0 10 20 30 40 50 100 MILES

0 20 40 60 80 160 KILOMETERS

EASTERN NORTH CAROLINA

F1gure A. Dramage network of eastern North Carolma and approximate extent of estuanes and sounds

saltwater front In this report a value of 200 mg/L of chlonde IS used to establish the saltwater front because that concentration clearly mdicates the presence of some seawater, and water with less than this amount IS usable for most purposes

Seasonal ranges m movement of the saltwater front are caused pnmanly by seasonal changes m freshwater m­flow and commonly are greater than daily ranges due to

tides alone In the Cape Fear River, for mstance, the sea­sonal range due to freshwater mflow IS typtcally 15 miles or more, whereas the range due to tides IS only about 3 to 6 miles

This seasonal movement of the saltwater front IS ba­Sically the product of two opposmg processes The saltwa­ter front tends to be dtsplaced downstream by mcommg freshwater On the other hand, the more dense saltwater

General Hydrology 3

tends to move upstream by mtxmg and dtffuston of salty water wtth fresher water upstream If these two processes are roughly m balance, there will be httle net movement of the front When freshwater mflows are htgh, then the tendency toward downstream displacement of the front by mcommg freshwater overwhelms the tendency toward up­stream movement due to mtxmg and dtffuston When freshwater mflows are low, the opposite ts true

Dunng and Immediately after penods of low fresh­water mflow, whtch typtcally occur m the late summer and fall m North Carohna, the landward encroachment of the saltwater front IS usually at tts greatest for the year Another factor whtch can contnbute somewhat to greater encroachment at thts ttme of the year IS that mean tidal level may be several tenths of a foot higher dunng November than, say, dunng July In the wmter and sprmg months, when freshwater mflow Is high, dtsplacement of the saltwater front seaward IS usually at Its annual maximum

OCEAN TIDES

The dnvmg force m the regular, pen odic fluctua­tiOns m estuanne stage, discharge, and movement of the saltwater front IS ocean tides Although the word "ttde" has often been used rather loosely to mclude water-level fluctuations caused by other forces, such as wmd and barometnc pressure, It IS considered m thts report to m­clude only those water-level phenomena caused by the gravitatiOnal attractiOns of the Moon and the Sun actmg on the Earth The movements of the Earth, Moon, and Sun relative to each other occur m cycles whtch, whtle complex, are predictable and repetitive This, m tum, re­sults m ttdes which occur m cycles that are also complex, but predictable and repetitive

Actually, the nse and fall of the water and the ac­companymg currents should be dealt with together, be­cause they are only dtfferent mamfestations of the same phenomenon, a tide wave However, for practical reasons, they are often dealt wtth separately, and the common En­glish usage IS to refer to the nse and fall of the water level as the ttde, and to the accompanymg currents as tidal cur­rents

The ttdal forces can be separated mto a number of components called partial tides The prmctpal partial ttdes are hsted m table 1 1 The parttal ttdes are charactenzed by thetr penods and a coefficient dtrectly related to the magmtude of the force producmg the partial ttde The par­tial-tide forces, when plotted agamst time, produce sme­hke curves of vanous magmtudes and penods which alter­nately remforce, then mterfere wtth, one another The re­sultant of all these partial-tide forces IS a senes of altemat­mg htgh and low tides of varymg magmtudes havmg a penod of 12 42 hours

4 Hydrology of MaJOr Estuar1es and Sounds of North Carohna

Table 1.1. The ten most 1mportant part1al t1des (Adapted from Schureman, 1924 )

Name of Period, Coefhcient

correspond1ng part1al tide 1n hours

Sem1d1urnal Pr1nc1pal lunar 12 42 0 4543 Pr1nc1pal solar 12 00 2120 Larger lunar ell1pt1c 12 66 0880 Lun1-solar 11 97 0576

D1urnal ~-solar 23 93 2655

Pr1nc1pal lunar 25 82 1886 Pr1nc1pal solar 24 07 0880

Long-Eer1od Lunar fortn1ghtly 327 86 0783 Lunar monthly 661 30 0414 Solar sem1-monthly 2191 43 0365

Figure 1 1 Is a graph of predicted h1gh and low tides for August 9-22, 1977, for the Cape Fear R1ver estuary at Wilmmgton, N C It clearly shows dmmal mequahties m the heights of the two htgh and two low tides each day These are caused pnncipally by the mteraction of the sev­eral semidmmal (twice daily) and dmmal (daily) partial tides (fig 1 2) The dmmal partial t1de remforces one of the semtdmmal tides and mterferes with the other, thus producmg the dmmal mequalities

When the range between h1gh and low t1de ts largest, the tides are called spnng tides, when the range IS smallest, they are called neap tides The recurrence m­terval of sprmg tides and neap tides IS 14 3 days They are caused pnmarily by the mteraction of the pnncipal lunar and pnncipal solar semidmmal tides These have shghtly dtfferent penods (12 42 and 12 00 hours, respectively) which result m altematmgly remforcmg then mterfenng with each other m cycles whtch take 14 3 days to com­plete The JUXtaposition of the two tide components dunng spnng tide and neap ttde IS Illustrated m figure 1 3 Dur­mg spnng tide the two components are nearly m phase with one another, dunng neap tide the two are almost completely out of phase The results of thts mteract10n are also Illustrated m figure 1 1, whtch shows that the range between predicted htgh and low tides dunng August 15-18 was greater than that dunng August 9-11

The long-penod partial t1des listed m table 1 1 are not as Important as the semtdmmal and dmmal compo­nents m controlling ttde heights but may make a differ­ence of about 0 5 foot seasonally m tide heights The ef­fects of these long-penod parttal tides are mcorporated mto the tide predictions of the NatiOnal Ocean Survey In addttion, allowances are made m these predictiOns for dif­ferences m seasonal tide heights due to mcreasmg or de­creasmg freshwater mflow m estuanes These differences may be more than a foot m some estuanes The N attonal Ocean Survey annually publishes tide he1ght and current predictiOns for a number of North Carolina coastal loca­tiOns

1-~a:: 6 ww

Wt-U..c:x 5 z~

-~ 4 wo 0-J 3 <X 1-z

2 (f) <X ow w::::!i! 1-uw

0 o> wo

" n (\ n n ,., r ,. h " n ('\ "' 1\ ' ~

\ " n " ' I I I II \

\ \

\ ~ I 1\J IU \. \ t l t l ~ l l \ L \ ~ \ a:: a:! -I a. <X 9 10 II 12 13 14 15 16 17 18 19 20 21 22

AUGUST 1977

Figure 1.1. T1de curve for Cape Fear R1ver estuary at Wdmmgton for August 9-22, 1977, based on pred1cted t1mes and he1ghts of h1gh and low water from Nat1onal Ocean SurveyT1de Tables

_.J

UJ >

3

...... -~ 2 UJ UJ<t u..LLJ

(/)

z

COMBINED COMPONENTS

~

~----~ DIURNAL / COMPONENTS

-3L---------------L---------------L---------------L-------------~ 0 6 12 18 24

TIME, IN HOURS

Figure 1.2 D1urnal mequallt1es produced from mteract1on of sem1d1urnal and d1urnal t1dal components (Adapted from Sverdrup, Johnson, and Flemmg, 1942 )

_.J

UJ >

-UJ 1- _.J

UJ UJ<t u..UJ

(/)

z z

-<t 1- UJ :z::::~ <..!)

u.~o :z::::...._ -I UJo ~UJ 1- a::

a:: UJ -3 u.. 0 UJ a::

2 4 6 8 10

SEMIDIURNAL TIDES -L- Pnnc1pal lunar part1al t1de

--s-- Pr~nc1pal solar part1al t1de

12 0 2 4 6 8 10 TIME, IN HOURS

12

F1gure 1.3. T1de curves at spnng t1de and neap t1de (Adapted from Sverdrup, Johnson, and Flemmg, 1942 )

General Hydrology 5

ESTUARINE FLOW

As mentioned earher, flow of water In an estuary can be descnbed as the superposition of tidal flow on the normal downstream nver flow Knowledge of the rates of movement of estuanne water and how rates and directiOn of movement vary are of great Importance In aiding navi­gatiOn, predicting the manner of movement and dtspersiOn of pollutants, and In understanding sedimentatiOn charac­tensttcs The purpose of thts sectton of the report ts to de­scnbe the most tmportant aspects of estuanne flow

The combinatiOn of nver flow and tidal flow wtll be referred to as ttde-affected flow In this report Ttde waves associated wtth the ttdal component of flow may have wave lengths of several hundred mtles or more When we reahze that most estuartes are much shorter than thts, tt ts clear that most estuaries can be occupied by only part of a ttde wave at any gtven time The behaviOr of an tdeahzed ttde wave In an estuary ts Illustrated In figure 1 4, whtch shows how water veloctty varies along the pro­file of a ttde wave propagating along a channel The wave here ts tdeahzed In that tt has assumed symmetry, ts prop­agating In a flmd of homogeneous dens tty, ts free from the effects of Internal and boundary fnction, and IS prop­agating without opposition from freshwater Inflow, bar­ners, or any other flow obstruction Note that the direc­tiOn of honzontal water movement at the wave crest Is al­ways In the directiOn of wave propagation, at the wave

troughs It ts In the opposite dtrectiOn Honzontal velocity IS zero halfway between the crests and troughs and IS maxtmum at the crests and troughs

Several other Interesting facts may be denved from figure 1 4 First, times of zero velocity do not coincide with times of htgh and low tide, as common sense might suggest Rather, times of zero veloctty (slack tides) occur about halfway between times of htgh and low tides Sec­ond, water In a tide wave may flow up-gradient, that Is, the water surface may be sloping downstream where the flow ts upstream

When the effects of freshwater Inflow, fnct10n, and any bamers (such as dams) are supenmposed on the flow pattern of an Idealized tide wave, velocity dtstnbutiOns relative to the crests and troughs are modified Freshwater Inflow, for example, wtll not affect the time of occurrence of htgh or low ttde, but will result In high slack water oc­cumng earher than otherwise and low slack water occur­nng later than otherwise Thus, as freshwater Inflow m­creases, high slack water will occur closer In ttme to high tide Also, the closer to the head of a ttde (or to a dam) one IS, the nearer In time are high water and high slack water Thus, In real estuanes, the above factors may con­siderably alter the velocity distnbutiOn along a tide wave from what might be predicted based on the Ideahzed Situa­tion portrayed In figure 1 4 (See later discussion of mea­surements of tide-affected flow In the Cape Fear and Northeast Cape Fear Rivers )

DIRECTION OF WAVE PROPAGATION

H1gh slack water

EQUILIBRIUM WATER i (

Low slack water

SURFACE -------------

Downstream 4

BOTTOM VELOCITY DISTRIBUTION

EXPLANATION

-----+Flood flow ....._ __ Ebb flow

Length of arrow 1nd1cates relat1ve velocity

Note Draw1ng not to scale Wave length may be several hundred m1les

F1gure 1.4. Behav1or of an 1deallzed t1de wave man estuary

6 Hydrology of MaJor Estuar1es and Sounds of North Carohna

Upstream ..

The wave form Itself propagates The speed with which It propagates Is referred to as wave celenty and IS equal to vgii, where g IS the gravitatiOnal constant and h IS the depth of the water m which the wave IS propagat­mg Thus, one can calculate the difference m time be­tween occurrence of high or low tide at different pomts along a total reach of known depth An Important pomt here IS that the wave celenty does not refer to the vel­ocities of mdividual water particles, but only to the speed of propagation of the wave form Actually, the wave form propagates much faster than mdividual water particles can move

Freshwater mflow to an estuary opposes the flood­tide flow and remforces the ebb-tide flow When freshwa­ter mflow IS larger than maximum flood-tide flows, net nver velocities will be downstream dunng all of a tidal cycle Otherwise, there will be twice-daily reversals of flow directiOn

One Important mfluence on estuanne flows which IS not usually signtficant m ordmary nver flow IS the Conolts effect due to the Earth's rotation In the northern hemisphere, the Conohs force tends to deflect a movmg particle to the nght of Its directiOn of motiOn On a flood tide, therefore, the water movmg upstream tends to hug the left bank (U S Geological Survey conventiOn assigns nght and left bank m the sense of facmg downstream ) On an ebb tide, the flow tends to hug the nght bank Because the net flow tn an estuary IS downstream, there IS an over­all tendency for flows to hug the nght bank With regard to saltmties, however, the observed tendency 1s for saltmties to always be higher on the left bank than on the nght dunng both flood and ebb tides Presumably, this IS because flood tides, which carry sahne water upstream, tend to hug the left bank, causmg higher sahmttes there, ebb tides, which carry fresher water downstream, tend to hug the nght bank

These observatiOns have obvious value m locatmg water mtakes for water supply or outfalls for waste water All other factors bemg equal, the nght bank would be the obvious chmce for the locatiOn of freshwater mtakes be­cause water may be less sahne (be of better quality) and for waste outfalls because flows on ebb tides would be greater (for better dtluttOn and transport of wastes)

SALINITY

At this pomt, the term "sahmty" needs to be more precisely defmed and discussed Saltmty refers to the de­gree of saltmess of water, or more specifically, the con­centratiOn of dissolved soltds m water The generally accpeted formal def1mt10n of sahmty was g1ven by Forch and others ( 1902) who defmed It as "the total amount of sohd matenal m grams contamed m one kilogram of sea-

water when all the carbonate has been converted to oxide, the bromme and 10dme replaced by chlonne, and all or­game matter completely oxidized " Even though this for­mal defimt10n refers to sahmty as an amount, m practice saltmty IS generally expressed as a concentratiOn, m part~ per thousand of seawater (%o) or milligrams per hter of dissolved solids ( 1 ,000 mg/L IS approximately equal to 1 part per thousand)

Average concentrations of the maJor constituents of seawater as determmed by Jacobsen and Knudsen (1940) are given below

Constuuent

Chlonde (Cl) Sodmm (Na) Sulfate (S04 )

Magnesmm (Mg) Calcmm (Ca) Potassmm (K) Bicarbonate (HC03)

Concentratzon (mg!L)

18,980 10,556 2,649 1,272

400 380 140

These constituents account for 34,377 out of the total of 34,482 mg/L of dissolved sohds m seawater Al­though these values are the standard used m this report, It should be recogmzed that concentratiOns of constituents m seawater vary from time to ttme and place to place For example, the dissolved-solids concentratiOn of 17 samples of seawater collected near Wnghtsville Beach, N C , by the U S Geological Survey between 1963 and 1965, ranged from 31 , 900 to 35,900 mg/L However, these vari­atiOns do not differ appreciably from the average of 34,482 mg/L of dissolved sohds and thus they are of mmor Importance m accountmg for sahmty variatiOns m North Carolina estuanes Even where the sahmty of sea­waters varies, the relative concentratiOns of maJor con­stituents remams constant-and the sahmty of a gtven water may be approximately determmed If the concentra­tion of any one of the maJor constituents of the water IS known For example, If the chlonde concentration of a given water sample IS 10,000 mg/L, then the sahmty IS 10,000118,980 X 34 5%o= 18 2%o

DetermmattOns of concentratiOns of tndiVIdual chemical constituents, such as chlonde, can be time-con­summg or otherwise Impractical m some SituatiOns Salin­Ity IS often determmed m the field by measurement of the specific conductance of the water The specific conduc­tance, measured m micromhos (J.Lmhos), Is proportional to the dissolved-solids concentration of the water Because the ratio of the concentratiOn of a given maJor constituent dissolved m seawater to the total dissolved-solids concen­tration of seawater IS almost constant, specific conduc­tance may be used to estimate the concentratiOn of any of the maJor constituents of seawater Such a relatiOn has been prepared for specific conductance versus chlonde and dissolved sohds (fig 1 5)

General Hydrology 7

u 0 It')

N

u 4000 0 It')

N

~ ct

(/)

0 :r::: 2

3000 0 a:: u

i

== 2000 w u z ct ~ u => 0

1000 z 0 u

u ~

u w ~ (/)

500 1000 1500 CHLORIDE CONCENTRATION I IN MILLIGRAMS PER LITER

DISSOLVED SOLIDS CONTENT, IN PARTS PER THOUSAND 0 2 4 6 8 10 12 14 16 18 20

28, 00 0 l--r--T"--r-""T"""'--r-~'T---r--+---r--+---r---r'---r---.-..L......r---r--"T----r---l.,.........,r--f--T"'"""""'1

~ 20,000r-----+-----l------+---_,_--l-----+------f ct

(/)

0 :r::: 2 0

Example If spec1f1c conductance 1s 12,000 J,Jmhos, chlonde concentration 1s 4000 mg/L

~ 16,000t---------r~r-----+-----~~--------~--------+-------~ 2

w u z ~ 12,000t---------r--------~-------4--------~--------+-------~ u => 0 z 0 u

QL-~._-L-L~~~-L-L-~~-L-L~~~L_L_~~--L~-L~~

0 2000 4000 6000 8000 10,000 12,000 CHLORIDE CONCENTRATION, IN MIll I GRAMS PER LITER

Figure 1.5. Relat.on between spec1f1c conductance and chlonde concentrations m North Carolma estuanes

8 Hydrology of MaJor Estuanes and Sounds of North Carohna

Chlonde IS a particularly Important constituent be­cause It IS often a hm1tmg element m determmmg smtabii­Ity of a water supply for pubhc or mdustnal use The Na­tiOnal Academy of Sciences (1972) [1974] has recom­mended an upper hm1t of 250 mg/L of chlonde for dnnk­mg water, and water with 500 mg/L or more IS unsUitable for a number of mdustnal uses Thus, the 200 mg/L of chlonde cntenon used m this report (equivalent to a spe­cific conductance of 800 J..Lmhos m figure 1 5) to md1cate the presence of saltwater IS w1thm the National Academy of Sciences' recommended upper hm1t for dnnkmg water

ESTUARINE TYPES

M1xmg of freshwater and seawater takes place through turbulent m1xmg and molecular diffusion The rates of m1xmg depend on channel geometry, the relative amounts of freshwater mflow and tidal flow, wmd, and the differences m density between seawater and freshwa­ter (Seawater has a specific gravity of about 1 025 as compared to about 1 000 for freshwater ) Most m1xmg situations produce one of three "types" of sahmty pat­terns-highly stratified, partially mixed, and well mixed Estuanes are often classed accordmg to which of these m1xmg patterns predommates Among North Carolina es­tuaries, examples of each type can be found It IS worth­while, therefore, to discuss the charactenst1cs of each

Highly Stratified Estuary

In a highly stratified estuary, the freshwater, bemg less dense, tends to nde over the top of the seawater (fig 1 6) VIscous shear forces along the boundary between the freshwater and seawater cause much turbulent m1xmg, makmg this a zone of rapid transition between freshwater and seawater Turbulence patterns w1thm this transition zone are such that the water has a net upward circulatiOn and seawater becomes entramed with the freshwater mov­mg downstream This phenomenon of upward breakmg waves has been discussed by, among others, Pritchard and Carter ( 1971) and Bowden ( 1967)

Thus, seawater directly below the transition zone re­tams Its sahmty, while freshwater above becomes more mixed with seawater as It moves further downstream FI­nally, at some downstream pomt, the water flowmg near the surface becomes md1stmgmshable from seawater The rapid sahmty change m the transition zone Is evident from exammat1on of sectiOn X-X' m figure I 6B

Net velocity under highly stratified conditions (fig 1 6B) IS downstream near the surface, IS drastically less m the transition zone, IS zero somewhat below the transitiOn zone, and then IS upstream m direction at greater depths If the velocities along this profile were mtegrated over a

penod of time, the resultant net flow would of course be downstream due to the energy gradient of the freshwater mflow This energy gradient accounts for the net down­stream flow m the upper levels of the nver, while the net upstream flow near the channel bottom IS from energy provided by gravitatiOnal convectiOn (Flows along the channel bottom due to gravitatiOnal convectiOn are often referred to as density currents ) The saltwater wedge, which would otherwise move upstream to the limit of tidal mfluence due to density differences between freshwater and seawater, IS constantly bemg eroded by contact and m1xmg with freshwater This lost seawater IS replaced by seawater movmg upstream along the channel bottom Thus, an eqmhbnum of the net position of the saltwater wedge may be mamtamed

A highly stratified condition may exist m an estuary only when the freshwater mflow Is large m relatiOn to tidal flow A rule of thumb giVen by Schubel ( 1971) IS that, m order to have highly stratified conditions, the vol­ume of freshwater entenng an estuary dunng a half-tidal penod (6 21 hours) should be at least as great as the vol­ume of water entenng dunng a flood tide In other words, the ratio of the freshwater volume to the flood-tide volume should be at least I 0 This ratio IS called the "m1xmg mdex " The rehab1hty of the m1xmg mdex m pred1ctmg the degree of estuary stratificatiOn IS mfluenced by chan­nel geometry As width mcreases or depth decreases, an estuary tends to become less stratified for a giVen m1xmg mdex

Partially Mixed Estuary

If the freshwater mflow becomes smaller m relatiOn to the flood-tide volume (w1thm a m1xmg-mdex range of about 0 05 to 1 0) then partially mixed conditions may prevail, as sketched m figure 1 7 A In this SituatiOn flow reversals will probably occur throughout the depth of the estuary durmg at least part of each tidal cycle (By con­trast, flow along the surface at some pomt m a highly stratified estuary may be downstream at all times and flow near the channel bottom m the saltwater wedge may be upstream at all times ) Under partially mixed conditiOns tidal flow dommates and the added turbulence from this source provides the means for erad1catmg the saltwater wedge Not only does seawater mix upward mto what was the freshwater zone, but freshwater mixes downward mto what under highly stratified conditiOns was a zone of sea­water The sharp mterface which separated the freshwater from the seawater m the highly stratified estuary IS re­placed by a much broader zone of moderate change m sa­hmty The saltwater front IS shown m profile m figure 1 7A, and other hnes of equal chlonde concentration would have similar attitudes The net changes m chlonde concentratiOn with depth through section Y-Y' (f1g 1 7B)

General Hydrology 9

DOWNSTREAM A

Sea WATER SURFACE R 1 ver

FRESHWATER

SALTWATER WEDGE I

.._I .... ~ ... x· CHANNEL BOTTOM

w w u u <{

8 Sect1on <{

u.. X-X u.. c Sect1on X-X 0::: 0 0:::

::::) ::::) 0 (/') (/')

0::: 0::: w w 1-- 10 1-- 10 <{

zone <{ Translf1on zone 3: 3:

---- -- -.-3: 20 3: 20 0 0 _J _J w w a::l a::l

1-- 30 1- 30 w w w w u.. u..

:z 40 I z 40 0 25 50 75 100 2 0 2

::c SALINITY, IN PERCENT I Downstream Upstream 1- 1-a.. OF SEAWATER a_ NET VELOCITY w w

IN FEET PER SECOND C) C)

Figure 1.6. A Net c1rculat1on patterns m a h1ghly strat1f1ed estuary B Sahmty profile through sect1on X-X' C Net veloc1ty profile through sect1on X-X'

1 0 Hydrology of MaJor Estuar~es and Sounds of North Carohna

are gradual The lack of a sharp mterface between fresh­water and saltwater IS apparent, but some degree of stratificatiOn remams

The vanatwns m net velocity with depth are not ob­VIous from the cuculatton arrows shown on ftgure I 7A, whtch show only that turbulent mtxmg ts present through­out a wide regiOn However, a defimte pattern does exist, as shown m figure 1 7C As m a highly stratified estuary, net velocities m the upper layers of the channel are down­stream and net velocities m the lower layers are upstream However, mstantaneous flow at a particular pomt m many partially mixed estuanes may be upstream or downstream at a particular moment at any depth

An unusual feature of flow m a partially mixed es­tuary IS that the rates of flow m both the upper and lower layers may be an order of magmtude htgher than nver flow For example, If F IS the freshwater mflow, the upper-layer net seaward flow may be 1 OF Smce the es­tuary as a whole IS neither filling nor emptymg, then 9F must be brought up the estuary from the sea m the lower layers Examples of this phenomenon have been venfied for the James River m Vugmia and the Chesapeake Bay (Pntchard and Carter, 1971, p IV-7)

Well Mixed Estuary

The thud maJor type of estuary IS termed well mixed Figure I 8A shows the profile of the saltwater front m a well mtxed estuary It ts nearly verttcal, whtch mdtcates that mtxmg forces are greater than m a parttally mtxed situation Schubel ( 1971) mdtcates that the upper hmtt for the mtxmg mdex IS probably about 0 05 for well mtxed conditions to extst In thts SituatiOn, freshwater m­flow IS very small m relation to tidal flow Because sahmttes are nearly homogeneous verttcally, dens tty cur­rents are negligtble Thus, veloctttes are umdtrectwnal from top to bottom at a gtven ttme m a gtven profile, as shown m ftgure 1 8C Wtth regard to salimty, although there may be some slight changes from top to bottom m a well mixed estuary (ftg 1 88), the changes are umform, wtthout the zone of more raptd change charactensttc of parttally mtxed and htghly stratified estuanes (fig 1 6B and I 7B)

The above dtscusstons provtde a framework for un­derstandmg salimty changes as related to circulatiOn pat­terns m estuaries Although three types of estuanes were dtscussed, tt should be recogmzed that there IS an almost contmuous spectrum of salimty and ctrculatwn patterns and that there are gradual transitiOns between the three types In fact, a gtven estuary may be htghly strattfted m the sprmg dunng penods of htgh freshwater mflow, par­tially mtxed m the early summer, and well mtxed m the fall when freshwater mflow ts mtmmum Wtthm the same estuary, for a gtven mixmg mdex, the mixmg type may

change as the saltwater front moves mto an area of chang­mg channel geometry The general rule wtth respect to channel geometry IS that an estuary tends to shift from a highly stratified to a well mtxed conditiOn wtth mcreasmg width and decreasmg depth (Schubel, 1971 , p IV -14)

SEDIMENT

The mechamcs of transport and depositiOn of sedi­ment m an estuary are far more complex than m ordmary streams Yet, because of the tmpact of sedtment deposi­tiOn on aquatic life and on navtgatton and because large sums of money are spent m dredgmg and mamtammg navtgatton channels and boat facthties, tt IS Important to develop a clear understandmg of the pnnctples of es­tuarme sedtmentatton

Sedtment, whether movmg m a free-flowmg stream or m an estuary, has two components-suspended sedi­ment and bed load Suspended sedtment composes parti­cles that are held m suspensiOn by the upward components of turbulent currents and finer parttcles that are held m collotdal suspensiOn Bed load conststs of matenal whtch ts too heavy to be held m suspensiOn but whtch moves by shdmg, rollmg, or sktppmg along the bed of a stream or estuary In a free-flowmg stream, however, net flow (and, therefore, sedtment dtscharge) ts always downstream and usually changes m magmtude slowly, whereas m an es­tuary the tide-affected flow (and therefore sedtment dts­charge) ts almost always changmg raptdly m magmtude and dtrectiOn Changes m chemtcal quality along streams are usually small and have negligtble effect on sedtment concentrations, whereas quite dramatic changes m chemi­cal quality occur wtthm estuanes and these may pro­foundly mfluence sedtment transport charactensttcs

In many estuartes, a charactenstic zone of high con­centratiOns of suspended sedtment and htgh turbidtty be­gms near the saltwater front and, m some estuaries, con­tmues downstream for miles Thts zone has been dis­cussed by, among others, Ippen (1966) and Schubel (1971) Upstream from thts zone, m the freshwater por­tiOn of the estuary, concentratiOns are less, downstream from thts zone, m the ocean, concentratiOns are also less The probable explanation for thts zone ts that such es­tuaries act as sediment traps Thts may be better under­stood by refemng back to the net CirculatiOn patterns m figure 1 6C for a highly stratified estuary lmagme sus­pended sedtment bemg carrted out to sea m the top layers of freshwater dunng ebb flow As the ttme of slack water approaches where the estuary wtdens towards the mouth or as the freshwater spreads out over the bays and adJacent ocean, velocities decrease, thus allowmg heavter sedtment parttcles to settle As they settle, they are entramed m water movmg upstream along the channel bottom At the upstream end of the saline water zone, flow circulates up-

General Hydrology 11

DOWNSTREAM A

~sea WATER SURFACE y

R 1ver

s I () () () ( l) '4<?-~s- '0

0 '4~1'1

0 () ~()

~ 10 I­<(

3:

20 3: 0 ......J w al 30 1-w w lL 40 z 0

Y)

u ~

CHANNEL BOTTOM

8 Sect1on Y- Y I

100 200 300 400 - NET CHLORIDE CONCENTRATION,

I

t- IN MILLIGRAMS PER LITER a.. w 0

I I

'0 yl

w

~ c Sect1on Y- Y I

~ 0 ::> U)

~ 10 t­<(

3:

3: 20 0 ......J w al 30 t­lJ..J w lL 40 z 2

I 1-a.. lJ..J 0

0 Downstream Upstream

NET VELOCITY, IN FEET PER SECOND

2

Figure 1.7. A Net c1rculat10n patterns m a part1ally m1xed estuary B Chlonde concentration profile through sect1on Y-Y' C Net velocity profile through section Y-Y'

12 Hydrology of MaJor Estuar.es and Sounds of North Carolma

DOWNSTREAM

w u <( ~

a: ~ U)

a:: ~ 10 <(

3:

3: 20 0 _. w CD

....... w w ~

30

A z .. Sea WATER I

() () l)

0 ~)() ~) 0

)

CHANNEL

8 SectiOn z-z I

z'

z 40 ....__ _ ____.. __ ---'-----1----'------1

0 100 200 300 400 :x:: NET CHLORIDE CONCENTRATION, 6: IN MILLIGRAMS PER LITER w C)

SURFACE R1ver

(J G () 0 (JD

() () () 0

BOTTOM

c SectiOn z-z· w u <( u.. a:: ~ (f)

0 ----~---~----~~--~ I

3: 20 0 _. LLJ CD

1- 30 w w LL

:r: 1-a.. w C)

I I

~I ~ ""'t-4-----+---....... -

0 Downstream Upstream

2

INSTANTANEOUS VELOCITY, IN FEET PER SECOND

Figure 1.8 A Net c1rculat1on patterns 1n a well m1xed estuary B Chlonde concentration profile through sect1on Z-Z' C Velocity profiles through section ~Z'

General Hydrology 13

ward and downstream, and sedtment parttcles may agam be entramed upward and flow toward the sea m the upper freshwater layers Agam, the parttcles may settle as vel­octtles decrease, and thus a sedtment parttcle may be caught m a loop pattern several ttmes

Thts sedtment-trap phenomenon IS found to some extent m htghly stratified SituatiOns, but ts even more pro­nounced m partially mtxed estuanes where net upstream velocttles near the channel bottom and net downstream veloctttes near the surface are much greater than m htghly strattfted estuanes Thts phenomenon ts probably not found to any stgmficant extent m well mtxed estuartes, where there IS no stgmftcant net upstream flow along the channel bottom

The sedtment-trap zones m estuanes are, naturally enough, zones of htgh sedtment deposition Most of the deposited sedtment m these zones ts of clay or stlt stze The particles tend to settle to the channel bottom wherever or whenever mstantaneous or net veloctttes suddenly de­crease or approach zero The tlp of a saltwater wedge ts one area of raptd deposttlon because net veloctty ts zero m that vtctmty Other potential areas of deposttlon are where tnbutanes enter a slow-movmg mam channel, m bays, and m boat shps

Another factor that may account for some sedtmen­tatton m the sedtment-trap zone ts flocculatiOn and sub­sequent deposition of clay-stzed particles m the water Thts process depends on the presence of electrolytes, such as sodmm chlonde, whtch neutrahze the electronegative charactenstlcs typtcally associated wlth sedtment parttcles Saltwater ts an electrolyte, and the setthng of fme-gramed parttcles ts mdeed observed m the salme water zone However, an add1t10nal or alternative bmdmg mechamsm brought about by ftlter-feedmg orgamsms has been ad­vanced by Schubel ( 1971) He descnbes the results of an extensive stze-analysts study of particles m suspensiOn at all depths m Chesapeake Bay and the Susquehanna Rtver He reports on p VII-20

Many compos1te part1cles were observed, particu­larly m the lower layer, but careful microscopiC exammat1on showed that most were agglomerates weakly bound by orgamc matter and mucus and probably produced by fllter-feedmg zooplankton Prellmmary expenments have md1cated that suspen­Sion-feedmg zooplankton probably play a maJor role m the agglomeration of fme part1cles m the water column, and m the subsequent depos1t1on of those part1cles The large population of fllter-feedmg zooplankton present m the Bay probably filter a vol­ume of water equ1valent to that of the ent1re estuary at least every few weeks, and perhaps every few days

Prev10us to thts statement Schubel stated that his evaluation techmques fatled to produce any evtdence of flocculatiOn In vtew of this, It might be safer to refer to these composite particles as agglomerates rather than floc-

14 Hydrology of MaJor Estuar1es and Sounds of North Carohna

culates An agglomerate IS a more general term meanmg a composite particle composed of two or more mdtvtdual particles held together by any relatively weak cohestve force A flocculate IS an agglomerate bounded by electros­tatic forces

Potential sources of stlt- and clay-stzed sedtment de­posited m a sedtment-trap zone are many Studtes of many Umted States estuartes have shown that sedtment from up­land dtscharge IS madequate m most cases to account for the shoahng rates that are observed m nver channels and harbors Ippen ( 1966, p 654) hsts other sources of shoal­mg matenal as follows

a) marsh areas adJacent to the estuary w1th runoff drammg mto the t1dewater,

b) matenals m larger estuanes bemg eroded from the shores by wave act1on and movmg by dens1ty currents mto the deeper port1ons,

c) matenals bemg d1splaced by dredgmg and propel­ler wash and moved by dens1ty or t1dal currents,

d) orgamc matenals as a result of the b1olog1cal cy­cles of estuarme plant and ammal env1ronment,

e) mdustnal and human wastes d1scharged mto the estuary,

f) wmdborne sed1ment In add1t10n to these sources mentiOned by Ippen,

sediment resuspended from the channel bottom and later redeposited m shoahng areas may also be an tmportant factor m htgh local shoahng rates m some estuartes In some cases, the open ocean adJacent to an estuary may also be a stgmftcant source of sedtment

Regardmg sedtment deposttlon, and attempts to tm­prove extstmg shoahng charactenstics, Ippen ( 1966, p 650) makes the followmg pomts

a) sed1ments settlmg to the bottom zone m an es­tuary will on the average be transported upstream and not downstream,

b) sed1ments will accumulate near the ends of the saltwater mtrus1on zone and form shoals Shoals w1ll also form where the net bottom veloc1ty 1s zero due to local disturbances of the reg1me such as by tnbutary channels,

c) the mtens1ty of shoalmg will be most extreme near the end of the mtrus1on for strat1f1ed es­tuanes and w1ll be more d1spersed m the well m1xed estuary

Therefore, w1th regard to human mterference m ex1stmg estuary patterns, the followmg general rules may be denved a) the maJor port1on of sed1ments mtroduced from what­

ever source mto an estuary dunng normal cond1t1ons will be retamed therem, and 1f transportable by the ex1stmg currents will be depos1ted near the ends of the sallmty mtrus1on, or at locat1ons of zero net bot­tom veloc1ty

b) any measure contnbutmg to a sh1ft of the reg1me to­wards strat1f1cat1on will cause mcreased shoalmg Such measures may be structures to reduce the t1dal flow and pnsm, d1vers1on of add1t1onal freshwater

mto the estuary, deepenmg and narrowmg the chan­nel,

c) dredgmg of channels should be accompanted by per­manent removal of the sed1ments from the estuary Dumpmg downstream 1s h1ghly suspect and almost always useless Ag1tat1on dredgmg falls mto the same category, 1f permanent removal IS des1red

Although the pnnciples discussed m this section are useful m understandmg general aspects of estuanne sedimentation, the actual movement and deposition pat­terns of sedtment m real estuaries are usually extremely comphcated m detail, and may require hydrauhc model studtes to defme adequately Model studies of thts kmd are lackmg for most sounds and estuaries m North Carohna Nevertheless, some mformatiOn about sedimen­tation m North Carohna sounds and estuanes IS given m later sectiOns of this report

EFFECTS OF WINDS AND HURRICANES

Most estuaries are thought of as freshwater mflow dommated, tide dommated, or some combmatiOn of both However, several maJor estuanes m North Carohna fall mto a less common category-wmd dommated

To understand how these wmd dommated conditiOns extst, first consider that the Outer Banks greatly weaken ocean ttdes m Pamhco and Albemarle Sounds and their tnbutanes For example, the mean tide range m the ocean off Cape Hatteras IS about 3 6 feet, accordmg to the Na­tiOnal Ocean Survey, while the range withm Pamhco and Albemarle Sounds Is less than half a foot Consider also that the channels of many estuanes west of the Outer Banks are very large for the amount of water they carry and that, consequently, velocities due to freshwater mflow mto them are often very low In this Situation of weak currents from both tides and freshwater mflow, wmd-gen­erated currents take on a relatively more Important role In addttiOn, the funnel effect of wmd-generated currents flowmg mto estuanes from Albemarle and Pamhco Sounds results m much stronger wmd-generated currents m those estuaries than would otherwise occur This com­bmation of circumstances results m wmd playmg a much more promment role m circulatiOn and mixmg patterns than would otherwise be the case

The physics of water movement m response to wmds IS extremely complex It IS sufficient for our pur­poses to consider that, owmg to fnction between movmg air and the water surface, a certam amount of water will be "pushed" m the directiOn toward which the wmd Is blowmg The amount of water moved depends upon sev­eral factors, the most Important of which are the velocity of the wmd, the contmuous distance along the water sur­face over which the wmd IS effective (called the fetch), and the depth of the water Movement of water by wmd

becomes Important when water levels adJacent to shorelines are adversely affected ObviOusly, onshore wmds cause water to pile up along the shore, and offshore wmds cause a lowenng of water levels

The mtenor shorelines of North Carolina have a complex configuratiOn, and It IS difficult to predict the ef­fects of a given wmd on water levels at a particular loca­tion However, with certam modificatiOns, the followmg equation (Bretschneider, 1966, p 240) may be applied with useful accuracy to some estuaries and sounds of North Carolina for predictmg wmd setup (change m water level)

s h[~-n](ll)

where

S wmd setup, or change m water level, h average depth, k constant empmcally evaluated at 3 3 x 10- 6 ,

X effective length of water surface over which wmd Is actmg, or fetch,

U wmd speed, n constant, which IS umty m a ngorous solutiOn

of the denvmg equation (Where calibratiOn data are available for a particular location, n can be empmcally changed to obtam more precise estimates of S ) , and

g acceleratiOn due to gravity

To use equatiOn I I to estimate the change m water level caused by wmds at some pomt along the shorehne of the sounds, It IS necessary to determme the component of wmd that wtll be effective m producmg the greatest change m water level at a pomt of mterest The effective component wtll usually be the component actmg along the longest contmuous lme of fetch to the pomt where the m­crease m water level ts to be calculated For a given wmd the component IS calculated from the angle of departure of the actual wmd directiOn from the effective lme of fetch By simple tngonometry the effective wmd speed ts

(1 2)

where

Ue effective wmd speed, U a actual wmd speed, and a angle of departure of wmd direction from the

effective lme of fetch

As an example of the use equatiOns 1 1 and 1 2, suppose the wmd Is blowmg from the east at 30 mi/h ( 44

General Hydrology 15

ft/s) The angle of departure of wmd dtrectiOn from a line perpendicular to the coast ts 20° The average depth along the fetch ts 40 ft The length of the fetch over whtch the wmd ts actmg ( dtstance perpendicular to the coast) ts 50 mtles (264,000 ft) Solvmg equation 1 2 ftrst

U, = (44 ft/s) (cos 20°) = (44 ft/s) ( 9397) = 41 3 ft/s

Solvmg equatiOn I I, for eventual wmd setup, S,

S = 40 [ 2(3 3xJ0-6

) (264,000) (41 3)2 +I -I]

32 2 (40)2 X -~ -

S = 40 [I 028439-1] = 40 [ 028419] = I 14ft

In practice, a curve ts plotted from equatton I 1 showmg S versus Ue Where posstble, actual observatiOn of S and U are used to adJust the constants m equatton I I and a final equatiOn ts developed whtch most accurately defines conditiOns at a parttcular locatton A "wmd compass" ts developed on whtch the vanous angles of departure m equation 1 2 are plotted as adJUStment coeffictents To de­termme setup for a gtven wmd at a gtven locatiOn, tt ts only necessary to use the wmd compass to determme the adJUStment coefftctent, multtply the actual wmd speed by thts coeffictent, and consult the "S versus Ue" curve for that location

Ltke most coastal areas, North Carolina's shorelines are affected by a full range of wmds, from gentle breezes caused by temperature dtfferenttals between land and ocean to vtolent wmds associated wtth maJor storm sys­tems Predtctable dmrnal and seasonal shtfts m wmd dt­rectton cause datly and seasonal shtfts m ttde hetghts and currents However, the most dramatic wmd effects are those associated wtth hurricanes, whtch seasonally threaten the eastern parts of the State Smce 1870, approx­Imately one hundred storms of humcane force have to some degree affected eastern North Carolina One of the most spectacular and destructive was Humcane Hazel whtch, on October 14, 1954, caused an estimated 100 mtllion dollars worth of wmd and water damage through­out the eastern one-thtrd of the State and forced saltwater further upstream mto the estuaries than ever recorded be­fore or smce

The effects of humcanes on water levels along the coast are extremely complex As Illustrated m figure 1 9, humcane wmds m the Northern Hemisphere ctrculate m a counter-clockwise pattern around an eye, usually from 50 to 75 mtles m dtameter, wtthm whtch wmds are calm to very hght Dependmg upon the position of thts eye rela­tive to a parttcular locatton, wmds assoctated wtth the storm may come from any dtrectiOn Should a part of the eye pass over the location, two penods of htgh wmd vel­octty separated by a penod of calm wtll be observed

16 Hydrology of MaJor Estuar1es and Sounds of North Carolma

Wmd dtrectiOns of the two htgh-wmd penods may be out of phase wtth one another by nearly 180 degrees Fahrenheit It ts also worthy of note that effective wmd speeds to the nght stde of these storms ( wtth regard to the general duect10n of motiOn) are greater than those on the left stde In the North Carolma area, humcane systems usually move at speeds of 5 to 40 mtles per hour, and thts forward motiOn 1s additive to wmd speed due to the coun­terclockwise mot1on of the c1rculat1on system

The overall effect of th1s complex pattern of hur­ncane wmds ts that resultmg water-level changes are even more complex At a gtven pomt on the shore, water levels may be etther ra1sed or lowered, or first ratsed then low­ered, or ftrst lowered then ra1sed The need to protect agamst humcane damage has led to the development of sophisticated mathematical models to pred1ct hurr1cane surge Although a complete dtscusston of these models 1s beyond the scope of thts report, the reader ts referred to Amem and Atran ( 1976) for a presentation of a mathemat­Ical model of cuculat10n and humcane surge m Pamlico Sound Later chapters of th1s report md1cate the suscepti­bility of many of North Carolina's coastal areas to hur­ncane-mduced floodmg

THE SALT-MARSH ENVIRONMENT

Thus far, we have been concerned only w1th general pnnctples of hydrology whtch w1ll be applied m descnb­mg the maJor sounds and estuanes of North Carolma m followmg sectiOns of the report However, the salt-marsh env1ronment, a umque and Important type of estuanne en­vironment, deserves some general dtscuss1on here, also

Much of the coastal fnnge areas of North Carolina's sounds and estuanes may be classified as a salt-marsh type of environment These areas are ecologically very Important for several reasons First, they serve as nurse­nes for a vanety of animals that are harvested m Important commercial and sport fishenes, these mclude shnmp, crab, scallop, and many fish spectes Second, salt marshes are very productive natural areas upon whtch many am­mats depend for food An estimated 65 percent of the total commerctal fishenes catch m coastal waters of the eastern Umted States ts made up of spectes that depend dtrectly m one way or another on salt marshes and estuanes dunng some phase of thetr life cycles (McHugh, 1966) The 1973 dockstde value of the.. North Carolina commerctal fishery harvest was about S 16 million, and the value ts mcreasmg every year (Thayer, 1975, p 62) In addttion, about $100 mtllion ts spent annually by North Carohna and out-of-state restdents for sport fishmg m coastal wat­ers of the State

As of 1962, North Carolina contamed about 58,400 acres of regularly flooded salt marshes and about 100,450 acres of Irregularly flooded salt marshes (W1lson, 1962)

45, f

40

20

83

20~ ~

80

+ J4o D 60 80

t2o 100 ~ 20 t 20 20t 20 m 1/h r

zat t 401

60 OF HURRICANE 80

(Calm)

/ t 20 ------+

80 83

~45

EXPLANATION

... 60

D1rect1on and wmd speed 1

1n m1les per hour

Fagure 1.9 The effect of forward mot1on of a hurncane on wmd veloc1t1es m each quadrant

The most abundant plants m these salt marshes are saltwa­ter cordgrass and needlerush, wtth grasswort and saltmeadow cordgrass occumng m lesser densities (Fran­kenberg, 1975, p 55) The pnmary productiVIty (plant production) of the salt-marsh environment IS pheno­menal-twenty times as productive as the open ocean and one to two orders of magmtude htgher than most other ecosystems-they are nvaled m productiOn only by tropi­cal ram forests and htghly cultivated land Table 1 2 gtves

comparative productiOn rates for the North Carolina salt marshes and various cultivated crops Plant matter from these lush salt-marsh areas IS consumed etther dtrectly by some manne ammals (such as shnmp, mullet, and zoop­lankton) or mdtrectly by others whtch eat the dtrect con­sumers

The salt-marsh environment, Important as It ISm the hfe cycles of many manne (and freshwater) orgamsms, IS a fragtle one-subJect to adverse effects from changes,

General Hydrology 17

Table 1.2. Pnmary product1on rates ofvanous ecosystems (Adapted from Odum, 1959, and Keefe, 1972 )

System

Hay - U.S. Average Highest (California)

Wheat - World Average Highest (Netherlands)

Corn - World Average Highest (U.S.)

R1ce - World Average H1ghest (Japan)

North Carol1na Salt Marshes

Net primary production rate, in pounds of plant material

per acre per year

3,738 8,366

3,497 11,867

6,102 11,442

5,686 13,597

Saltwater Cordgrass (Spartina alterniflora) regularly flooded 11,570

5,429 irregularly flooded

Needlerush (Juncus roemarianus) regularly flooded irregularly flooded

Saltmeadow Grass (Spartina patens) regularly flooded irregularly flooded

not only from a wide vanety of natural phenomena, but also from encroachment by man PollutiOn, landfill and dredg10g, bmld10g, dra10age of marshes, and alteration of freshwater flow regtmes are some of the acttvtttes of man that either destroy or have adverse effects on the salt­marsh environment and manne orgamsms whtch are di­rectly or 10duectly dependent on It Tthansky and Meade (1974) estimated that, nationally, we are losmg for fishery production about 1 percent per year of our total estuanne environment The annual percentage lost from salt-marsh areas may be even htgher

Many of the problems associated wtth mamta10mg a viable salt-marsh environment are related to changes m hydrology, etther natural or man-mduced Heath ( 1975) reported on the hydrologic tmpact of agncultural develop­ments 10 the Albemarle-Pamhco regiOn, many of whtch affect the salt-marsh areas He po10ted out that dramage canals bmlt 10 conJunction with large-scale corporate farrn10g developments remove freshwater runoff to the

18 Hydrology of MaJor Estuaries and Sounds of North Carohna

9,834 6,034

11,534 8,837

coast more qmckly than the previous natural system Dur-10g penods of heavy runoff through dramage canals, sahmties may be reduced m salt-marsh areas to the pomt where young shnmp and other marme spectes sensitive to low sahmties are forced out of the protective food-nch muck of the salt marshes mto more-salme unprotect1ve sandy-bottom areas where conditions are much less favor­able for their survival

H1gh sedtment loads are another problem associated wtth htgh flows and also with construction actiVIties Clay-sized particles, particularly, may harm bottom-dwell-10g and filter-feed10g organisms by cloggmg their feedmg apparatus and hampenng burrowmg activities

Many salt-marsh areas are affected to some degree by pollutiOn from agncultural areas Thts pollution may be of several types-high levels of total coliform bactena, fecal coliform bactena from human and ammal wastes, pesticides, and mtrogen and phosphorous (nutnents which may promote destructive algal blooms)

2. Hydrology of the Cape Fear River Estuarine System

Together, the lower Cape Fear and Northeast Cape Fear Rtvers compnse what we wtll term the Cape Fear Rtver estuanne system (See pl I ) Actually, the North­east Cape Fear Rtver basm (dramage area-l ,740 mt2

) IS a subbasm of the Cape Fear RIVer basm (total dramage area-9, 140 mt2

) and the Northeast Cape Fear Rtver es­tuary may be thought of as a branch of the Cape Fear Rtver estuary Nevertheless, for ease of analysts the Northeast Cape Fear Rtver estuary wtll be dtscuo;;sed sepa­rately

The Cape Fear Rtver and the Northeast Cape Fear Rtver estuanes are the only maJor estuanes m North Carolina havmg a relatively free and dtrect access to the ocean, whtch results m stgmficant tides and tide-affected flow wtthm them In the Cape Fear Rtver estuary, tides extend up to Lock I, about 65 mtles upstream from the mouth near Southport As shown m plate I , the mouth IS at a nver cross section extendmg from Fort Caswell east to the western tip of Smtth Island Ttde effects m the Northeast Cape Fear Rtver estuary extend about 48 miles from Its mouth at Wtlmmgton, whtch m tum IS located about 28 mtles upstream from the mouth of the Cape Fear Rtver estuary

The lower reaches of the Cape Fear Rtver and Northeast Cape Fear Rtver estuanes are subject to saltwa­ter mtrus10n, sometimes rendenng the water unsUitable for some uses Plate 1 shows the approximate extent of salt­water mtrus10n m both estuaries, that IS, the furthest up­stream advance of water contammg 200 mg/L of chlonde ever known and the furthest upstream advance that has a 50-percent chance of bemg equaled or exceeded m any year

Raptd mdustnal growth has taken place along the banks of the two estuanes m recent years, and a number of mdustnes use the water from them as process water and dtscharge mdustnal wastewater mto them

The Cape Fear Rtver and Northeast Cape Fear Rtver estuanes are Important navigable waters, and navtgatmn channels are mamtamed to vanous depths by the U S Army Corps of Engmeers The channel dtmenswns roam­tamed for navigatiOn wtll be dtscussed m more detail m followmg sections of thts report

The summanes of the hydrology of the Cape Fear Rtver and Northeast Cape Fear Rtver estuaries are based on data and other mformatJon from vanous sources, pnmanly the Geological Survey Plate I shows the loca­tiOn of key flow and water-quality statiOns operated m the Cape Fear Rtver basm by the Geological Survey These

statiOns mclude the Cape Fear Rtver at Phoemx (sta 02107570), where the Geologtcal Survey generated re­cords of volumes of water flowmg upstream and down­stream durmg each ttdal phase for the penod Apnl 1966 through March 1969 Data from these stations are pub­lished annually m the U S Geologtcal Survey water-data report senes for North Carolina Wtlder and Slack (197la and 1971 b) summartzed data on chemtcal quality of streams m North Carohna from 1943 through I967 Wtl­der and Hubbard ( 1968) reported on saltwater encroach­ment m the Cape Fear Rtver estuary, Hubbard and Stamper ( 1972) reported on the movement and dtspersmn of soluble pollutants m the Northeast Cape Fear Rtver es­tuary, the U S Army Corps of Engmeers ( 1976) dtscussed sedimentation and related aspects of hydrology m the lower Cape Fear Rtver estuary These and other sources of mformatton are acknowledged m the text where appro­pnate

THE CAPE FEAR RIVER ESTUARY

The Haw and Deep Rtvers, two maJor tnbutartes of the Cape Fear Rtver, ongmate m the Ptedmont Provmce and flow southeast, JOining at Moncure, to form the Cape Fear Rtver (pl I) From Moncure, the Cape Fear Rtver flows southeast through the Coastal Plam to Its mouth near Southport The Cape Fear Rtver drams a larger part of North Carolina than any other nver, the dramage area at the mouth IS 9,140 mi2

, all of whtch ts m North Carolina Of this, the Deep Rtver accounts for I ,422 mt2

and the Haw RIVer accounts for I, 705 mt2 Other maJor tnbutanes mclude the Black Rtver (I ,563 mt2

) and the Northeast Cape Fear Rtver ( 1, 740 mt2

)

Pnor to the construction of Lock 1 about 37 mtles upstream from Wilmmgton, nver stage was affected by ocean tides posstbly as far as 50 to 75 miles upstream from Wtlmmgton The constructiOn of Lock 1 elimmated the effect of ocean ttdes above this pomt and thts lock, therefore, marks the upstream limtt of ude effect at the present time The total length of the estuary from tts mouth to Lock I IS about 65 miles

The lower part of the estuary, begmmng about three mtles below Wtlmmgton, averages about a mtle m wtdth and contams numerous scattered Islands and a few ttdal flats It resembles an elongated bay only a few feet deep except along the shtp channel whtch has been dredged and mamtamed m thts reach to depths of 32-40 feet and wtdths of 300-500 feet By comparison, the channel above Wtlmmgton Is narrow, wtth depths rangmg from 20 to 60 feet Ttdal currents m the upper reach, particularly near the lower end are strong and velocities may exceed 3 ft/s

Hydrology of the Cape Fear R1ver Estuarme System 19

0

Flow

Flow m the Cape Fear Rtver estuary ts strongly tide­affected Except dunng penods of htgh freshwater mflow, regular reversals of flow occur wtth each ttde Dunng penods of htgher-than-average freshwater mflow, outflow at some or all locatiOns m the estuary may be htgh enough to overwhelm mcommg flood tides, resultmg m penods when no flow reversal occurs Because the freshwater m­flow ts such an tmportant component of flow m the es­tuary, 1t wtll be dtscussed at length before further constd­ermg ttde-affected flow

Freshwater Inflow

The average dtscharge at the mouth of the Cape Fear Rtver estuary ts about 11 ,000 ft3 Is Because of the dtfftculty of accurately measunng flows m the estuary portiOn of the nver, values for dtscharges were amved at by summatiOn of flows for gaged areas wtthm the basm and esttmates of flows for ungaged areas

The maJor part of the freshwater mflow 1s measured at the stream-gagmg stations shown on plate 1 The sta­tiOns closest to the estuary gage the runoff from 6,660 m12

or 73 percent of the total 9,140 m12 of dramage area above the mouth of the estuary The three stattons of greatest Im-

portance are the most downstream stations on the Cape Fear, Black, and Northeast Cape Fear Rtvers The runoff from 6,500 m12 of the Ptedmont and the mner part of the Coastal Plam 1s measured at the three stations hsted below

Number Name 02105769 Cape Fear Rtver at Lock 1 near

Kelly 02106500 Black Rtver near Tomahawk 02108000 Northeast Cape Fear Rtver near

Chmquapm

Dramage area 5,220 ml 2

These stattons wtll be referred to as Lock 1, Tomahawk, and Chmquapm, mdtvtdually, and collectively as mdex gages

The largest ungaged areas are m the lower part of the Coastal Plam, the area adJacent to the estuary Itself Most of the runoff from the total area of 2,640 m12 below the mdex stations 1s ungaged However, a relat10nsh1p be­tween the runoff from thts ungaged area and the combmed runoff at the Tomahawk and Chmquapm stattons was es­tabhshed by obtammg penodtc base flow measurements at sttes m the ungaged areas and relatmg these on a per square mtle basts to concurrent dtscharges at Tomahawk and Chmquapm (ftg 2 1) These two stations were used m the relatiOn because they dram only areas m the Coastal Plam The net outflow from the estuary 1s the sum of dts-

20 Hydrology of MaJor Estuar.es and Sounds of North Carohna

0

charges for the three mdex statiOns plus that contnbuted by the ungaged area, whtch can be esttmated from figure 2 1

Because steady-flow condtttons rarely occur throughout the Cape Fear Rtver basm, lag-time corrections must be apphed to streamflow records at the vartous gages m order to arnve at an estimate of freshwater outflow from the estuary at a gtven ttme Lag times, computed from theones of wave celenty and rounded to the nearest whole day, are 2 days from Tomahawk to the mouth of the Black Rtver and 3 days from Chmquapm to the mouth of the Northeast Cape Fear Rtver

Combmmg all flow components, the followmg em­ptncal equation was developed for estimatmg freshwater outflow (Q,) from the estuary,

where

Q,

total outflow from the estuary, dtscharge at Lock 1 at day of Q,,

(2 1)

dtscharge at Tomahawk two days pnor to Q,,

dtscharge at Chmquapm three days pnor to Q,, and

runoff obtamed from ftgure 2 1 usmg Q2 + Q3

EquatiOn 2 1 was used to calculate average 7-day out­flows The 7 -day penod was chosen because 1t was long enough to dampen the effects of mmor, locahzed varia­tiOns m the pattern of basm runoff and short enough to be a sens1t1ve parameter for relatmg mflow to the pos1t10n of the saltwater front

Insofar as water supply, sewage dllut10n, and salt­water encroachment m the Cape Fear Rtver are concerned, the most cnttcal flow penods are usually those of sus­tamed low flow Ftgure 2 2 shows the average recurrence mterval, m years, at whtch vartous average 7-day mmt­mum flows may be expected to occur These values were generated by combmmg estimated annual 7-day mmtmum flows for the variOus flow components of equatiOn 2 1 It ts mterestmg to note that tf releases from the B Everett Jordan Reservmr (pi 1) are controlled accordmg to the current operatmg schedule, then the mmtmum flow of the Cape Fear Rtver at Ltlhngton 1s expected to be no less than 600 ft3/s Based on thts, the mtmmum dtscharge at the mouth, near Southport, mtght be about 800 ft3/s, com­pared wtth an estimated 300 ft3 /s wtthout the reservmr for the 7-day, 1 00-year mtmmum net dtscharge near South­port

0 z 0 u w Vl

~ 1000~------------------~~-------------------------------------------r----~~-­f­w w LL

u iii ::::> u

~ z a: < ::::> 0 z

I I :I:

u Example If the sum of the diSCharges at 1

Tomohawk and Ch1nQu0p1n 1S 300 ft 3/s, 1 0 z < :..:

runoff from the 2,640 m• 2 of ungoged 1

area >n the Cope Fear R1ver bos1n 15 ------~~~------------~1~------~-----------------3: < :r: < :::i!

obout 430 tt 3/s 1

~ ~ Vl w (!) a: < :r: u Vl 0 LL 0

I I I I I I I I I :::i!

::::> Vl 10~----~--~-L-L-L~~------~--~_L-L~~~------L-~__ll_L_L.~~------~~~--~~~~~

I 100 1000 10,000

RUNOFF FROM UNGAGED AREA, IN CUBIC FEET PER SECOND

F1gure 2.1. Concurrent d1scharge relat1on for est1matmg runoff from the ungaged dram age area between the mdex stat1ons and the mouth of the Cape Fear R1ver estuary (Mod1f1ed from Wilder and Hubbard, 1968 )

T1de-affected Flow

Flow of the Cape Fear Rtver estuary ts strongly In­

fluenced by ocean ttdes The U S Geological Survey op­erated a ttdal dtscharge gagmg station near Phoemx (sta 021 07570) from Apnl 1966 through March 1969 (See fig 2 3 ) The purpose of thts station was to develop mfor­matiOn on tide-affected flows for the estuary which could prove useful, for example, m better understandmg the movement and dtspersiOn charactensttcs of water sub­stances discharged to the nver or m better understandmg the mechamcs of sedtment transport and deposition Vol­umes of water flowmg upstream and downstream on each tidal phase were published m the annual data reports of the U S Geologtcal Survey CalibratiOn measurements were made over full or nearly full ttdal cycles on three oc­casions--May 11-12, 1966, March 8, 1967, and July 27, 1967

Parttal results of the March 8, 1967, senes of mea­surements are shown m figure 2 4 Thts senes of measure­ments was made under fairly typical ttde-affected flow conditiOns and provtded, wtth other mformat10n, a means to calculate the mmtmum freshwater mflow reqmred to prevent flow reversals m the vtctmty of Phoemx

Figure 2 4 shows that the maximum measured dts­charge on March 8, 1967, was 15 ,400 ft3 Is downstream at 1500 hours on ebb ttde By contrast, the maxtmum dts-

charge on flood ttde was 6,690 ft31s upstream at 1915 hours The average flow over the ttdal cycle was 6,240 ft3 Is downstream at the Phoemx gage Thts value appears reasonable compared wtth the estimated freshwater flow at Phoemx for March 8 of about 6,500 ft31s From thts mfor­matiOn, It appears that little or no upstream flow should occur near Phoemx whenever the freshwater mflow ex­ceeds about 13,000 ft31s Downstream from Phoemx, the ttdal component of flow would be larger and a corres­pondmgly larger freshwater mflow would be reqired to prevent flow reversal Upstream, the ttdal component would be less and the freshwater mflow reqmred to pre­vent reversal would be less also

Two other facts from figure 2 4 are worth notmg First, ttmes of htgh and low ttdes do not occur simultane­ously wtth times of htgh and low slack water Rather, slack water occurs from one-half to one-and-a-half hours later than high and low tides Second, the duration of downstream flow IS about 8 hours, the duratiOn of up­stream flow Is less than 4 hours These durations are more and less than the expected 6 21 hour duration of a tidal phase unaffected by freshwater mflow As freshwater m­flow mcreases, the duratton of downstream flow also In­

creases Figure 2 5 shows typtcal vanat10ns of velocity wtth

depth m the Cape Fear Rtver Thts particular profile was taken at the Atlantic Coast Lme Ratlroad Bndge at

Hydrology of the Cape Fear R1ver Estuanne System 21

0 z 0 (..)

UJ (/)

a:: UJ CL.

t-UJ UJ IL.

(..)

CD ~ (..)

z

3: 0 _J

IL.

t-~

0

1000

Example A 7-day annual m1n1mum flow of 1,000 ft 3/s has a recurrence 1nterval of 2-7 years

100~------L-__JL_L_L_L_ __ ~----~L---~~--L-L-~-L--------L---~--~~~~~~ I 01 I I 12 I 5 2 3 4 5 6 7 8 9 10 20 30 40 50 100

RECURRENCE INTERVAL, IN YEARS

Figure 2.2. Magmtude and frequency of annual mammum 7-day average net flow of the Cape Fear Raver estuary at the mouth, near Southport

Navassa (see fig 2 3) on May 13, 1966, dunng a senes of discharge measurements on the Cape Fear River es­tuary The manner of variatiOn of velocity With depth ts typtcal of hundreds of profiles made on this and other days Velocities are very umform with depths from withm 5-10 feet of the surface to withm 5-10 feet of the channel bottom, then drop off sharply near the bottom Velocities at the surface are usually only slightly less than at depths of 5-10 feet, but wmds may cause near-surface velocities to mcrease or decrease Pomt velocities due to tides alone m the Navassa-Phoemx reach seldom exceed 2 ft/s The particle distance traveled up or downstream due to tides alone IS m the range of 6 to 8 miles m this reach Vel­ocities and travel distances due to freshwater mflow would have to be added to those due to tides to determme actual velocities and travel distances m the estuary

Water Quality

Summanes of water quahty of mflowmg freshwater at three key Sites m the Cape Fear River basm are shown

22 Hydrology of MaJor Estuar1es and Sounds of North Carohna

m table 2 1 Generally, mimmum concentratiOns of dissol­ved constituents occur dunng high freshwater flows com­posed mostly of overland runoff, which IS typically low m dissolved sohds Conversely, maximum concentratiOns of dissolved constituents tend to occur dunng mm1mum streamflows, whtch are composed largely of more-htghly­mmerahzed ground water Except for color and Iron, con­centrations of maJor constituents of mcommg freshwater fall Withm hmits for dnnkmg water recommended by the U S Environmental Protection Agency ( 1976) [ 1977] However, the North Carolina Office of Water and A1r Re­sources (1972, p 27-103) states that the rap1d mdustnah­zatiOn which has taken place along the Cape Fear R1ver estuary, particularly by chemical mdustnes, has resulted m a vanety of chemical substances bemg discharged mto It, rendenng 1t unfit, even where fresh, for dnnkmg and some other uses Without expensive treatment The report further states that synthetic orgamc compounds released mto the estuary by petrochemical mdustnes may be a par­ticularly dtfftcult treatment problem because these com­pounds restst destructiOn by commumttes of mtcroor­gamsms used to treat ordmary sewage m waste treatment

N

0

0

Du Pont PI ant s 't e

2

2 MILES

F S Royster Ferttltzer PI ant

3 KILOMETERS

Phoen1x

EXPLANATION

A Gag1ng stat1on

-2 R1ver miles measured upstream from Market Street 1n Wllm1ngton Market Street 1s 27 5 miles upstream from the mouth of the Cape Fear R1ver estuary

---1.,_• 01rect10n of flow

Gage near Navassa 02107571

V77A Caroltna Power and ~ Ltght Company Plant

Figure 2.3 Cape Fear R1ver estuary upstream from Wllmmgton

plants Heatmg of the estuary water from power-plant op­eratiOns and mdustnal-coolmg operatiOns may be a sigmfi­cant problem along some reaches If not for contamma­twn, the water, where fresh, would be sUitable for most mdustnal, domestic, and agncultural uses

Supenmposed on difficulties m freshwater use due to contammation are difficulties due to saltwater mtruswn, whtch may at times affect water quality as far as 20 miles upstream from Wilmmgton Details of saltwater mtruswn m the estuary are given later

Hydrology of the Cape Fear R1ver Estuarme System 23

~ ~

::::z::: -< Q. a 0 ~ s. ~ .!! ~ ITI :a. c ~ ; "' Dl = Q.

~ c = Q.

"' s. z Table 2.1. Summary of chem1cal analyses of freshwater samples collected at key stations m the Cape Fear R1ver basm Chem1cal constituents shown are m ~ milligrams per liter, except spec1f1c conductance, pH, and color (From W1lder and Slack, 1971a) :r ~ Dl

2. s Dl Station

number

0210SSOO

02106SOO

0210aooo

Station name

Cape Fear River at William 0 Huske Lock (Lock 3) near Tarheel, N C

Black River near Tomahawk, N C

Northeast Cape Fear River near Chinquapin, N C

Drainage Period area of

mi 2 sampling

4,alO Oct 1946 to

Sept 1967

6aO Oct 19S2 to

Sept 1967

600 Oct 19SO to

Sept 1967

.., "' c:

~ Sampling ., -; frequency "'Cll

Cll co "" a ., ., ~

Cll .. t)

.. Cll ... c: ... > .....

~ )(., ... l&l "'

daily Hax 13 0 3S Min 1 6 01 Avg 7 6 06

monthly Hax 12 94 Min 2 6 01 Avg 7 2 21

monthly Hax 14 a3 Min 1 3 01 Avg 6 9 2S

-;;o ;:G -;;;- X ~

~ -;;;- ~ Cll 0 u ... "' ~ a :z: a ., ~

:I ~ :I c: a ... ...

~-=-,., Cll :I "' a .. ... ... Cll :I "' .. o ., t) c: ... ., asu ....

..... co .., ... ~c. ..... ., ., 0 0 :I u X "' .... oQ "'

s s 2 2 21 2 6 e47 14 2 0 6 2 7 6 a 2 s 3 s 1 3 a 0 1 s 18 6 2

s 2 1 9 a 2 2 2 17 14 1 4 2 2 s 7 3 2 1 3 1 9 4 4 1 1 7 7 s 4

17 3 3 33 3 7 47 29 2 a 2 7 2 4 a s 3 1 2 a 6 1 2 14 s a

I Dissolved Hardness .....

t) 0 ~ solids as CaC01

::I.C 0 .., a ..... 1: .., ~

c: 0 u 0 0 .. ~ ~ :z: ... .., a !l o;.: ....

~ !l ., Cll :I

Cll Cll ... .... as oX~

~ :::: Cll ., Cll ., a., d ..-4'-'~ ... .c ::IU ..... :I Cll 0 .... .. ., A ..,. :I ~;, ..0 ... Cll .. 0 0 .. .. ... 0 t) I .. t) t) 0 ..... :I ... 0 OlC:O ..... o: a c:.,

!~:; .....

.c ..... ... .c Cll.-< ., 0 t) :c 0 u "" :z: .... ..: u u :z: "" u

lS 0 s 4 0 0 69 a7 7S 21 a 142 a a ao 3 2 0 0 00 41 30 10 0 4S s a 3 6 7 2 1 0 la S2 44 14 2 77 3S

7 7 3 2 3 10 70 4a 19 17 as 7 0 220 2 s 0 0 00 44 23 6 1 37 s 1 20 6 2 7 6 03 S6 33 11 s S3 74

S2 s 6 9 10 163 92 S6 S2 267 7 6 200 3 6 0 0 00 32 23 9 2 39 s 1 30

14 2 1 6 03 70 4a la a as a9

0 16,000 z 0 u UJ

1000 1400 1200 1600 2000 2200 1800

! . • • 1 • ! .. ~ . l (/)

a: 12,000

UJ . Cl..

1-::E

UJ <t 8000 UJ

UJ

u... a: Ebb t 1 de volume 1-(/)

u 333 m ill1on CUbIC feet z Q) 3: => 0 u 0

z

UJ- ::E (,!) <t a: UJ

<t a:: :I: 1-

u (/)

Cl.. (/)

=> 0

4000

0

4000

8000

7 1-UJ

6 UJ LL.

z 5

- 4 UJ (,!)

<t 1-(J)

3

)

I ! ~ 11

H1gh t1de

f-

I

I H1gh slack water

·~ _.-- Low slack water

I

Flood t 1 de 1volo-me

69 mlll1on CUbiC feet

. I I •

I .. i

. ! •. I ! ... ...

-

i. I . -i . . 'WL Low t 1d e I 2

0800 1000 1200 1400 1600 1800 2000 2200 TIME, IN HOURS MARCH 8, 1967

F1gure 2.4. Stage and d1scharge of the Cape Fear R1ver estuary near Phoemx on March 8,1967

w u ex: u.. a:: ::;)

(/)

a:: w t-ex: ~

~ 0 _.J

w CD

t-w w u..

z

:I: t-

0

10

20

30

40

50

~ 60 a 0

I I I I

tJ

p

v

p

D

)

n,;t I

I CH~NNEL 1 BOTTOM I 2 3

DOWNSTREAM VELOCITY, IN FEET PER SECOND

F1gure 2 5. Vanat1on of veloc1ty w1th depth of the Cape Fear R1ver estuary at Navassa on May 13, 1966 (at meter stat1on 20,0759-0803 hours)

Sediment

The Geologtcal Survey has made suspended-sedi­ment determmat10ns from monthly samples collected at Lock I near Kelly (station number 02105769 on pi I) smce January 1973 The average suspended-sedtment load there ts about 920 tons/day or 336,000 tons/year Parttcle­stze analyses (Stmmons, 1976) show that over 90 percent of thts matenal ts of stlt or clay stze ( 062 mm or less) The fate of thts sedtment has not been completely studted, but tt ts known that some ts depostted m the estuary The U S Army Corps of Engmeers estimates that, m order to mamtam navtgatJOn facthttes at the Mthtary Ocean Termi­nal at Sunny Pomt (MOTSU), about 18 mtles downstream from Wtlmmgton, 2,238,000 cubtc yards, or about 3 5 mtlhon tons, of sedtment must be removed annually at a cost of $2,169,000 (US Army Corps of Engmeers, 1976, p. 4) Thts gtves some tdea of the economic tmpact of sedtmentatwn m the estuary

Note, from the above dtscusston, that the amount of matenal removed from the estuary through dredgmg far exceeds the amount entenng by way of Lock 1 Addt­twnal fluvtal sedtment entenng the estuary from the Northeast Cape Fear Rtver and other subbasms probably

Hydrology of the Cape Fear R1ver Estuarme System 25

does not exceed 35,000 tons/year Therefore, the pnmary source of the new shoahng m the Sunny Pomt area could not be new fluvtal sedtment, but must be denved from wtthm the estuanne reach or elsewhere-from slumpmg along the channel, from shore erosiOn, from old spml areas, or posstbly from sedtment denved from the ocean

Salinity

Variations 1n Time and Space

The Cape Fear Rtver may be classified under some flow conditiOns as a parttally mtxed estuary That ts, tur­bulence ts sufftctent to prevent formatiOn of a dtstmct salt­water wedge or tongue, yet there remams a deftmte sahn­tty gradtent wtth depth Thts IS Illustrated m ftgure 2 6, whtch shows typtcal longttudmal variatiOns m chlonde concentratiOns of the Cape Fear Rtver at a htgh slack water on November 1, 1967 The gradtent IS accounted for by the denstty dtfferences between freshwater and salt­water The less dense freshwater tends to flow on top of the heavter saltwater These denstty dtfferences are also responstble for upstream denstty currents whtch may occur along the channel bottom These have been observed at and near the Mthtary Ocean Termmal at Sunny Pomt where a predommant upstream or flood flow extsts at times m the lower porttons of the nver water column (U S Army Corps of Engmeers, 1976, p 2)

A dtfferent vtew mdtcattve of sahmty stratificatiOn ts shown m ftgure 2 7, whtch ts a cross sectiOn showmg chlonde concentratiOns of the Cape Fear Rtver estuary 1 5

miles upstream from Market Street, Wtlmmgton, on June 5, 1962 The top-to-bottom dtfferences are very marked The surface concentratiOn of 150 mg/L of chlonde ts eqUI­valent to less than one percent seawater while the bottom concentration of 3,000 mg/L or greater ts at least 16 per­cent that of seawater

The sahmty of the estuary ts m a state of constant flux Sahne water moves m and out of the Cape Fear es­tuary regularly m response to ttdal actiOn, freshwater m­flow, wmds, and a number of other, less stgmftcant, fac­tors However, It has been found, at least for the part of the estuary above Wtlmmgton, that the relattve positiOns of the vartous hnes of equal chlonde concentratiOn are fatrly constant In other words, tf we know the nver mtle posttton of 300 mg/L of chlonde, then the posttiOn of 200 or 1,000 or 3,000 mg/L of chlonde may be predtcted wtth a fatr degree of accuracy, provtded that the locatiOns are somewhere above Wtlmmgton Thts relatiOn ts shown m ftgure 2 8 The values gtven are for the channel bottom at htgh slack water Values at the surface would be some­what less

The maxtmum upstream movement of saltwater m the Cape Fear Rtver estuary probably occurred dunng the passage of Hurrtcane Hazel on October 15, 1954 The eye of the hurrtcane moved mland near the South Carohna border and proceeded m a northerly dtrectiOn along a path that crossed the upper end of the estuary The coun­terclockwise circulatiOn of wmds around the humcane eye produced strong wmds from the southeast whtch ratsed ttdes to the htghest level ever recorded at Wtlmmgton The htgh tide measured at the Nattonal Ocean Survey's

Water surface

f­w w u..

-:I: f­a.. w 0 EXPLANATION

t-----+--- 3000- Chlorrde concentratrons rn mrllrgrams per lrter Vertrcal scale greatly exaggerated

80L---~--~---L--~--~--~----~--~--~--~----~--~--~--~--~--~~--~--~--~--~ 0 2 3 4 5 6 7 8 9 10

MILES UPSTREAM FROM MARKET STREET, WILMINGTON

Figure 2.6. Long1tudmal vanat1ons m chlonde concentrations of the Cape Fear R1ver estuary at h1gh-slack water, November 1,1967 (From Wilder and Hubbard, 1968 ) (Refer to f1g 2 3 for locations )

26 Hydrology of MaJor Estuar1es and Sounds of North Carohna

1-w w I.&...

z

0

Water surface 0 150

------~------------~~200 --------~--------------~------

--L-------------~-500----------~-------------+----

2000

----------r--------------~3000

40J-----~~rt~~~~==t====:==~=+~~~~~~~------~ Note : Vert tcal exagg.erati"d'n:;.;:y

5 times .

100 200 300 ---500-Chloride concentrations in

milligrams per liter

400 DISTANCE FROM LEFT BANK, IN FEET

500

Figure 2.7. Variations in chloride concentrations in a cross section of the Cape Fear River estuary 1.5 miles upstream from Market Street, Wilmington, on June 5,1962. (From Wilder and Hubbard, 1968.)

a:: w f-

_J

a:: w Cl..

(/)

~ c::x: a:: <.::>

:::::i _J

~

z

z 0

f-c:::r a:: f-z w u z 0 u

w 0

a:: 0 _J

I u

7000

5000

4000

3000

2500

2000

1500

1200

1000

BOO 700

600 500

400

I I

7 300

v 200

0

/ v I

I I ·-v

·--1- -

I I I - -

L---~-/~1 -

-

20,000

15,000 u 0 LO

12,000 N

I-10,000 <.{

/ v I Example: If near-bottom conductance at one

/ point during high slack water is known to be --1220 mg/L chloride (4100 ,umhos), then near-I bottom high slack water conductance 2 miles - _ downstream would have been about 4000

BOOO (/)

0 I ~

6000 0 a:: u -, mg/L chloride (12,000 ,umhos) -- 5000 ~ =r=:;- I It I

-f-

EXPLANATION -des are shown for near bottom

-

1-- of channel at high slack water -

4000 z

w 3000 u

z c::x: f-u

~ - r--I 1-

-

::)

2000 0 z 0 u

- - - - --1- 1500 u

1- 1200 LL

u 1- 1000 w

Cl..

1- (/)

BOO 2 3 4 5 6

DOWNSTREAM DISTANCE, IN MILES

Figure 2.8. Relation between chloride concentration and specific conductance at a known point in the Cape Fear River estuary and chloride concentration and specific conductance at other points either upstream or downstream. Relation applies only to reaches upstream from Wilmington.

Hydrology of the Cape Fear River Estuarine System 2 7

Wtlmmgton gage was 7 9 feet above mlw (mean low water), the next htghest recorded tide, corrected for nver stage, ts only 5 6 feet above mlw (See ftg 2 10 ) Al­though the posttton of the saltwater front dunng the pas­sage of Humcane Hazel was not observed, tt ts esttmated that tt reached a posttton more than 20 mtles above Wtl­mmgton (pi 1) At the same time, tt ts estimated that the saltwater front on the Black Rtver, a maJor tnbutary to the Cape Fear Rtver, reached a positiOn about 15 mtles up­stream from tts mouth (pl 1) The freshwater 10flow to the estuary as measured at Lock 3 dunng the seven days precedmg the hum cane averaged about 290 ft3 /s Thts ts the lowest esttmated mflow dunng the penod of record (1938-1982) at Lock 3 Thts accounts, 10 part, for the ex­treme encroachment of the front whtch, tt ts 10ferred, must have taken place on October 15, 1954

The movement of the saltwater front 10 response to semtdmmal tides ts of particular Importance to 10dustnes and others wtthdraw10g water from reaches of the nver

7000

6000

5000

4000

whtch may be subJect to saltwater mtruswn By carefully scheduling withdrawals, tt ts often posstble to obta10 freshwater from the estuary throughout much of each tidal cycle Htgh slack water, bottom-chlonde condtttons gtven m figure 2 8 represent the htghest chlonde concentrations which usually occur dunng a tidal cycle and are of rela­tiVely short duration Figure 2 9 shows the approxtmate number of hours dunng a tidal cycle that near-bottom chlonde concentratiOns may be expected to exceed 200 mg/L for vartous maximum concentrations at high slack water It IS Important to note that this relation apphes only upstreatn form Wilmmgton This figure shows that, unless the chlonde concentration at high slack water exceeds ap­proximately 5,500 mg/L, It t~ possible to obtam freshwa­ter from the estuary for some part of the tidal cycle For example, It mdtcates that wtth a maxtmum chlonde con­centration at htgh slack water of about 2,000 mg/L, It IS posstble to obtam freshwater for about 7 hours of the total 12 42-hour ttdal cycle

20,000

__ L.---1-I

~ I--" ,.,.

I

5,000 u 0

a:.-LU 3000

v //

2,000 ~

10,000 ~ I-<(

~ ~ u :5

2000 cna:. LU

::I: I-C!:l:J I a:. 1-LU 1500 <(a..

zcn 0~ _<( t-a:. <((,!)

f=:::i 1000 z= LU~ u zz 800 o-u

~ / -f.-- Example A chlonde concentration of 2000 mg/L

occumng at h1gh slack water md1cates that there w1ll _,.._

/ be 5 hours when the chlonde concentration IS greater '--than 200 mg/L and 7 hours when the concentration 1s less than 200 mg/L

v -I

/ -f-

/ II

8000

7000 6000

5000

4000

3000

LU 0 cc 600 0 ...J ::c u 500

400

300

/ I f-

v I .... v f-

200 0 2 3 4 5 6 7 8 9 10 II 12

2000

1500

1200

1000

800

NUMBER OF HOURS CHLORIDE CONCENTRATION EXCEEDS 200 MILLIGRAMS PER LITER

Figure 2 9. RelatiOn between chlonde concentration near the bottom of the Cape Fear R1ver estuary upstream from Wll­mmgton at h1gh slack water and the number of hours the chlonde concentration will exceed 200 mg/L near the channel bottom (From W1lder and Hubbard, 1968)

28 Hydrology of MaJor Estuar1es and Sounds of North Carohna

(/')

0 X :::e 0 a:: u :::e z

-LLJ u z <l ........ u :::;, 0 :z 0 u

u u: u LLJ Q._ (/')

Relation of Salimty to Freshwater Inflow and Tides

The distances upstream and downstream that the saltwater front moves m response to tides depends of course on the volumes of water transported by the tides These volumes are reflected, m a general way, by the rel­ative heights of high and low tides Other factors bemg equal, the higher the tide, or senes of tides, the farther upstream the front will move Thus, tide heights can serve as useful mdexes to semidmmal saltwater movements

The NatiOnal Ocean Survey (formerly the U S Coast and Geodetic Survey) has operated a tide gage at Wilmmgton smce 1935 Data on tidal heights were also obtamed by the Geological Survey at Its stage statiOns on the Cape Fear River near Phoemx and Navassa, from Apnl 1966 through March 1969 Figure 2 10 shows the number of years the observed highest annual tide equaled or exceeded mdicated heights above mean low water at Wilmmgton dunng 1935--66 Neglectmg the effect of se­nal correlatiOn, the probability of occurrence of a highest annual tide of a given magmtude at Wilmmgton can bees­timated from this curve

-

Wilder and Hubbard ( 1968) related the positiOn of the saltwater front at high slack water to the previous 7-day average freshwater discharge at the mouth, as deter­mmed from gagmg statiOn data and the use of figure 2 1 and equatiOn 2 1 They were able to adJUSt the relatiOn for the effects of varymg tide heights Details of the develop­ment of these relations are contamed m their report, but the final relation IS presented m figure 2 11 This figure contams a family of curves for selected tide heights show­mg the estimated position of the saltwater front for differ­ent rates of mflow Approximate results may be obtamed by mterpolation between the curves

Frequency of occurrence of mimmum annual m­flows and highest annual tides have been presented earher m figures 2 2 and 2 10 Combmmg data from these fig­ures to obtam the maximum annual encroachment of the saltwater front presents several problems Two of the more sahent of these are ( 1) the nonrandom distnbutwn of tide height and mflow dunng a year, and (2) the possibil­Ity of the Simultaneous occurrence of high tides and low mflow, neither of which are annual extremes, but which, m combmation, may produce the maximum encroach­ment However, If one of these parameters IS held con-

z 10 Q: Q: e ~ 7~--,_--~----+----+----~---r--~----~---+----+----+----r---,_ __ _, ____ ,_ __ _, <I w ~~ w~ Z<l Z<l

i~ w~ ~~ ~~ ~ ~ Example The hrghest annual trde equaled or ._

9 ~ ~

~ .., 6

exceeded 4 5 feet (Natrona! Ocean Survey • U) -J

-- .c. datum) 21 of the 32 years from -+----1 z

w~ 1935-66\ ~~ ==~ ·~ =>~

: ~ ~·--~ 8 ~ ~ <I 0 • :----r--.. 0

::> CD 5 • .-·~ \ W CD ~c:::r • ·- o<l

<I ~ ~ • .......__,_,: ~ ~ ~~ ~· _J~ ~ lL_ ----·--:_.-:..._ 7 ~ lL_

G z 4r---4----+----+----+----~--~---+----+----+----~---r--~----4----+----~·~~~- ~ z :r • <I

3~--~--~--~--~--~--~--~--~~--~--~--~--~--~--~----~~ :r

0 4 8 12 16 20 24 28 32 NUMBER OF YEARS INDICATED HIGHEST ANNUAL TIDE WAS EQUALED OR EXCEEDED

FROM 1935-66

F1gure 2.10. Magmtude and frequency of hrghest annual trde m the Cape Fear Rrver estuary at Wllmmgton, corrected for component of nver stage due to freshwater mflow (From Wilder and Hubbard, 1968 )

Hydrology of the Cape Fear R1ver Estuarme System 29

10,000 '\. ' \ \ 1 I I I lll '\. \ \

\ \ \ 1\

~ \ \ \ 0

~ 5000 u w (f)

~ \ \ \ ' \ \ \ \ ' \ a:: w a.. ~ \ \ ' ' \ t' ~ \ ~

~ w w lJ....

u aJ ~

u

:z

w (.!)

1000 a:: c::r

"' ~ 1\ ~ Po~\~ \;~ 1\~ G' l'

~ c.J' "'

~ \1\\ ~ \ ~ \

' '\. \ \ \ \ I u " ~ '~ \ \

, ~

(f)

0

w

~ ' \\ \ \

" '\ ~\ \ \ \ Ill.. (.!)

c::r a:: 500 w > c::r

r--- Example A 7-day average d1scharge " "'\ ,\ \ ~~ of 1000 ft3/s and a h1gh t1de of 3 0 ft

"" '"" \ ~\ \ w1ll result 1n 1ntrus1on of the 200

>- mg/L 1sochlor to about 7 m1les ~ ,, ~ \. ' c::r 0

I

upstream from Market Street 1n W1lm1ngton at h1gh slack water

r-

100 I I I I I I I 4 5 5 6 7 8 9 10 12 15 20

DISTANCE I IN MILES UPSTREAM FROM MARKET STREET, WILMINGTON

Figure 2.11. Interrelations of max1mum encroachment of 200 mg/L chlonde, outflow at the mouth, and t1de he1ghts m the Cape Fear R1ver estuary (Rev1sed vers1on of relat1on developed by Wilder and Hubbard, 1968)

30 Hydrology of MaJor Estuaraes and Sounds of North Carohna

stant, probabthttes may be determmed wtth reasonable ac­curacy For example, usmg ftgure 2 11 and assummg that the maxtmum tide wtll be 4 0 feet above mean low water dunng the penod of annual mtmmum flow, tt may be that encroachment to a pomt 10 mtles above Wtlmmgton wtll occur when the 7-day average outflow ts about 820 ft3/s, and we esttmate from ftgure 2 2 that such a flow condttton wtll recur on an average of 3 8 years

It IS apparent, from ftgure 2 11 that saltwater en­croachment wtll not be a problem as far upstream as 15 mtles above Wtlmmgton, near the mouth of the Black River, without the simultaneous occurrence of both an ex­ceptiOnally htgh ttde and an exceptiOnally low mflow

Another tmportant factor that wtll affect the extreme annual position of the saltwater front ts the B Everett Jor­dan Reservotr The operatmg scheme for thts reservmr provtdes for a mmtmum flow of 600 ft3/s m the Cape Fear Rtver at Ltlhngton Thts reservotr release, plus the mmt­mum mflow that may be expected to occur about once m 100 years, on average, between Ltlhngton and the mouth, wtll produce about 800 ft3/s of outflow from the estuary Thts augmented flow should constderably reduce the maxtmum extent of saltwater encroachment m the estuary

THE NORTHEAST CAPE FEAR RIVER ESTUARY

The Northeast Cape Fear Rtver (see pi 1 and fig 2 12) ongmates m Wayne County, flows south through Duphn, Pender, and New Hanover Counttes, and at Wtl­mmgton flows mto the Cape Fear Rtver, which empttes mto the ocean about 30 mtles south of Wtlmmgton The total area dramed ts 1, 740 mt2 The entire basm hes wtth­m the Coastal Plam and stream gradtents average less than one-half foot per mile The two largest tnbutanes are Rockftsh Creek and Holly Shelter Creek Much of the mam stem of the Northeast Cape Fear River and most of tts tnbutanes are typtcal black-water, swamp-dramage streams, wtth Impercepttble flows, sand-detntus bottoms, and low turbidtty Ttde effects m the Northeast Cape Fear Rtver extend upstream almost 50 mtles from the mouth, to near Holly Shelter Creek Thus, the nver may be con­stdered an estuary m that 50-mtle reach Many of the tnbutanes entenng the Northeast Cape Fear Rtver m tts ttdal reach are also affected by ttdes

The lower 2 5 mtles of the Northeast Cape Fear Rtver estuary has been dredged and a navtgattOn channel 32 feet deep and 300 feet wtde ts mamtamed Upstream from thts, to a pomt 48 mtles above the mouth, the nver was cleared to a depth of 6 feet m 1896, upstream from thts, to 56 mtles above the mouth, the nver was cleared to a depth of 3 feet

EXPLANATION

02108500

• Stream-gag1ng stat1on

y Water qual1ty stolion

N

0 10 MILES

0 10 15 KM

F1gure 2.12. Northeast Cape Fear R1ver estuary

Several mdustnes use the Northeast Cape Fear Rtver and Its tnbutartes both as a source of process water and as a conveyor of mdustnal wastes The upper reaches of the Northeast Cape Fear Rtver are used for recreatton, pnmanly boatmg and ftshmg

Freshwater Inflow

The average net outflow of the Northeast Cape Fear Rtver estuary ts about 2,120 ft3/s Of greater mterest than average flow, however, are low flows, because pollutiOn

Hydrology of the Cape Fear R1ver Estuarme System 31

and saltwater mtruston problems are greatest dunng low flows In the Northeast Cape Fear Rtver, an attempt toes­timate low flows at the mouth by stmple extrapolatiOn of the measured low flow at Chmquapm, based on dram age­area rattos, wtll lead to erroneously htgh results Thts ts because, dunng low-flow penods, the upper part of the basm contnbutes a proportionately htgher percentage of flow than does the lower part of the basm For thts reason, a relatiOn was developed by Hubbard and Stamper ( 1972, p E21) relatmg the low flow at Chmquapm to the flow at the mouth The relatiOnship, shown m ftgure 2 13, provtdes a rehable approximatiOn of total freshwater flow out of the Northeast Cape Fear Rtver only dunng stable low-flow recessions, when flow at Chmquapm IS less than 360 ft3/s Therefore, the relationship should not be ex­tended beyond the hmtts shown

0 z 0 -uiOO~----------,_-------,~-+----------~

:J:w ,_<n ~

Oo:: ~w

0..

1-

<t~ ;s:W 3 ....... lL.U t-­~<D

/ /

I 0 G 10~--------~,_-----------+----------~

/ /

/

~~~--~~~~--~~~~~--~~~~~

I 10 100 1000 FLOW Ar CHINQUAPIN, IN CUBIC FEET PER SECOND

Figure 2.13. Relat1on between flow measured at Northeast Cape Fear R1ver at Chmquapm and net outflow from the Northeast Cape Fear R1ver estuary at the mouth (Adapted from Hubbard and Stamper, 1972 )

Another Important aspect of low flows ts frequency of recurrence Figure 2 14 shows low-flow frequency curves of net outflow from Hubbard and Stamper ( 1972) These curves may be used to estimate the frequency of re­currence of vanous annual mmimum consecutive-day av­erage outflows For example, a mtmmum annual 7-con­secutive-day average mflow of about 15 ft3/s or less ts ex­pected to have an average recurrence mterval of about 1 0

32 Hydrology of MaJor Estuaries and Sounds of North Carohna

years The flow relations presented m thts sectiOn of the report can be used, as dtscussed later, to develop relatiOns showmg the frequency of recurrence of saltwater mtrus10n m the Northeast Cape Fear Rtver estuary

Tide-affected Flow

Ttde ranges m the Northeast Cape Fear Rtver es­tuary vary considerably dependmg on dtstance upstream from the mouth at Wtlmmgton At the General Electnc plant, 6 4 mtles upstream from the mouth, mean tide range IS about 3 4 feet, near Castle Hayne, 23 mtles up­stream from the mouth, they average about 1 7 feet, near the mouth of Holly Shelter Creek, 50 miles upstream from the mouth, there are no lunar ttdes

Flow due to ttdes ts the dommant flow component m the lower reaches of the Northeast Cape Fear estuary Strong flow reversals occur near the mouth wtth each tidal cycle Here, nver veloctttes due to tides average about 1-1 5 ft/s, and seldom exceed 2 ft/s Although no specific mformat10n IS available on velocities due to tides m the upper reaches of the Northeast Cape Fear Rtver estuary, they would become mstgmficant near nver mtle 50

The average freshwater mflow to the estuary IS about 2,100 ft3/s At thts rate, average veloctttes near the mouth due to freshwater mflow alone are only about 0 08 ft/s, or 5 to 8 percent of the average velocities attnbutable to ttdes

The U S Geological Survey made a contmuous measurement of tide-affected dtscharge dunng one com­plete ttdal cycle, 6 4 miles upstream from the mouth of the Northeast Cape Fear estuary, on October 23, 1969 The results of the measurement are shown m figure 2 15 The maximum dtscharge measured on October 23 was 22,250 ft3/s Thts occurred dunng flood tide at 1930 hours The maxtmum dtscharge measured on ebb tide was 18,080 ft3/s at 1400 hours These values are much larger than the estimated 420 ft3/s of freshwater mflow for that day Durmg ebb tide, a total of 315 mtlhon cubic feet of water flowed past the measunng section Of this amount, only about 11 mtlhon cul}tc feet could be accounted for by freshwater mflow to the estuary Thts represents about 3 percent of the total flow volume

ObviOusly, tides are the dommant short-term flow component near the mouth of the Northeast Cape Fear Rtver estuary A freshwater mflow of about 23,000 fe/s, almost 11 ttmes the average, would have been reqmred to prevent flow reversals dunng the October 23 measure­ments, and flows as large or larger than 23,000 ft3/s occur only about 0 02 percent of the time Further upstream, the mfluence of tides on flow IS less and becomes neghgtble about 50 mtles upstream

As m the case of the Cape Fear Rtver estuary, times of htgh and low tides m the Northeast Cape Fear Rtver es-

500

0 z

100 0 u lLJ

:I: (/)

t-:::> a:: 0 lLJ ~ ~

t- t-<[ LLJ lLJ

~ lL.. 0 ..J lL.. u 1- CD :::> :::> 10 0 u

----------------------7: Example 1n text 1

z I I I I I I I I

2- I

I 01 I I 15 2 3 4 5 10 20 30 50 100 RECURRENCE INTERVAL, IN YEARS

F1gure 2 14. Low-flow frequency curves for the Northeast Cape Fear R1ver estuary (Adapted from Hubbard and Stamper, 1972)

tuary do not comcide with times of slack water, as shown m figure 2 15 Dunng the October 23 measurement, slack water occurred more than an hour after high and low tides

Detailed vertical velocity profiles are not available for the Northeast Cape Fear River estuary However, based on some velocity observatiOns made dunng the Oc­tober 23 measurement, profiles would be Similar to those observed dunng measurements of the Cape Fear River es­tuary, shown ear her m figure 2 5

Dunng October 1969, a study of the movement and dispersiOn of dye m the Northeast Cape Fear River estuary was made by the U S Geological Survey The results of this study are contamed m the 1972 report by Hubbard

and Stamper Figure 2 16, taken from that report, shows average flushmg times for a solute InJected mto the es­tuary about 6 5 mi1es upstream from the mouth When a solute (or pollutant) IS InJected as a slug, It travels up­stream and downstream with flood and ebb flows As It does so, It spreads out and becomes diluted, formmg a cloud of the solute In addition to the upstream-down­stream movement of the cloud due to tidal flows, there IS a net downstream movement of the cloud due to freshwa­ter mflow This cloud has a center of mass and It IS the flushmg time of the center of mass to which figure 2 16 refers For example, refemng to figure 2 16, If the out­flow IS 200 ft3/s, It would take 30 days for the center of mass to reach the mouth from 6 5 miles upstream At this

Hydrology of the Cape t-ear R1ver Estuarme System 33

0800 1000 20,000

16,000

0

~ ~ 12,000 uc:r . ww en a::

1-8000 a::(/)

wz a..3:

0 .

1-0 4000 w .

w u..

u CD 0

H1gh slack water'\

"-" ~ u

z 4000

w-~ (.!)<r Flood t 1 de a::W c:rO:: 8000 zl-u<n (/')a.. -~ 0

12,000

16,000 .

20,000

24,000

6

1- 5 w w

I . . . l l ~

t1dej H1gh u.. 4 z

3 1-

w 2 (.!)

c:r 1-en 1-

0 0800 1000

1200 1400 1600 1800

l I . l .

Ebb t 1 de vo I u me

315 m1ll1on CUbIC feet

.1

Low slack water

Flood t 1de

. . .

l . . . . . . . . . . .. • • I . . .. . . . . . ~....__ L~w t 1 de

1200 1400 1600 TIME, IN HOURS

OCTOBER 23, 1969

I I 1800

2000

i . . . i

J . . -

-

-

2000

F1gure 2.15 Stage and discharge as measured contmuously dunng October 23,1969, m the Northeast Cape Fear R1ver es­tuary, 6 4 miles upstream from the mouth

34 Hydrology of MaJor Estuar1es and Sounds of North Carohna

V>

~ IOOr---------~-r------------+-----------_, 0

<.!)

z J: V>

~ IOr------------r---r----~--+-----------~

IL-~~~~LU~---L~~LLLUL---L-~~~~ 10 1000 10,000

OUTFLOW, IN CUBIC FEET PER SECOND

F1gure 2.16 Average flushmg t1me for a solute InJected mto the Northeast Cape Fear R1ver estuary about 6 5 miles up­stream from the mouth (From Hubbard and Stamper, 1972)

time, one-half of the solute would already have passed the mouth and one-half would not yet have reached the mouth The results of thts analysts can be extended up­stream and downstream for dtfferent InJectiOn pomts by usmg cross-sectiOnal areas and average freshwater m­flows Then, mean veloctttes for a gtven reach may be de­termmed by the equation

where

v Q

A (2 2)

V mean veloctty, m feet per second through the subreach

Q freshwater mflow, m cubtc feet per second

A area, m square feet

Dtvtdmg the length of each subreach by the mean vel­octties gtves net travelttmes, whtch are based on freshwa­ter mflow, dtsregardmg ttdal effects

Hubbard and Stamper ( 1972) also gtve maxtmum concentration bmldups at vartous nver cross sectiOns due to vartous constant InJectiOn rates of a solute 6 5 mtles up­stream from the mouth They found that the dye cloud dts­persed upstream and downstream several mtles from the InJectiOn pomt but that maxtmum solute concentratiOn bmldup was only 0 3 mtles below the InJectiOn pomt It ts dtfficult to extrapolate thetr results upstream or down-

stream for other InJection pomts m the Northeast Cape Fear Rtver estuary, but maxtmum concentratiOn bUildups would be expected near the InJeCtiOn pomts

Water Quality

Summartes of the chemtcal quality of water at three key sttes m the Northeast Cape Fear Rtver basm are gtven m table 2 2, mcludmg observed ranges and average values of maJor chemtcal constituents Iron concentrations some­times exceed the 0 3 mg/L concentratiOn IImtts recom­mended by the U S Environmental ProtectiOn Agency ( 1976) [ 1977] for public water supplies The same ts true for color, whtch often exceeds the upper IImtt of 75 color umts recommended by the Environmental ProtectiOn Agency ( 1976) [ 1977] The color of the Northeast Cape Fear Rtver ts denved pnmartly from decaymg vegetatiOn and the leachmg of humtc actds m swamp areas

Sediment

The sedtment-carrymg capactty of the Northeast Cape Fear Rtver and Its tnbutartes IS low due to low stream gradtents Most of the sedtment that ts earned ts of clay or stlt stze (less than 0 062 mm) Based on flow and sedtment measurements made at Northeast Cape Fear Rtver at Chmquapm and Rockfish Creek near Wallace, the average annual sedtment mflow to the estuary ts prob­ably no more than about 15,000 tons (20,000 cubtc yards) Thts amount ts less than one-thtrd of the esttmated 66,000 cubtc yards of sedtment that the U S Army Corps of Engmeers removes on an average annual basts from the Northeast Cape Fear Rtver estuary to mamtam navtgatwn

ObviOusly, the amount of sedtment from upstream sources ts not enough to account for the amount of mamtenance dredgmg that ts done m the estuary The questiOn then anses, what ts the source of the sedtment that forms shoals m the navtgatton channel and harbor fa­Cilities m the Northeast Cape Fear Rtver estuary? Thts question can be answered only speculatively because .little work has been done to determme the exact sources Prob­ably only a part of the estimated 20,000 cubtc yards of sedtment that ts earned mto the estuary by freshwater m­flow actually settles m the estuanne zone Ltkely, a large proportiOn of It ts earned out mto the Cape Fear Rtver es­tuary However, sedtment that ts depostted from upstream sources would tend to settle m the deeper dredged areas

A second posstbthty ts that some shoaling matenals may be transported upstream from the Cape Fear Rtver Thts could occur whenever the Northeast Cape Fear es­tuary ts m a parttally mtxed or stratified state Then, net upstream flow mtght prevail near the bottom The mmt-

Hydrology of the Cape Fear R1ver Estuarme System 35

!oN a'l

:I -< Q.

0 0 ~ s. ~ Dl Q ..

1"1"1 ~ c Dl .. ;; Ill Dl

= Q.

~ c = Q. Ill

s. z 0 :s. ~

t""l Dl

2.. :; Dl

s n

0

Table 2.2 Summary of chem1cal analyses of water samples collected at key stat1ons m the Northeast Cape Fear R1ver basm (adapted from W1lder and Slack, 1971a) Chem1cal constituents are m m1ll1grams per liter, except spec1f1c conductance, pH, and color

...... OJ.saolved Hardneaal :,_

: N ...... l ~ ...... ~ ::::;- ...... ..., 2~ aoll.ds ucaco3 1 1 ~!-i tation "' 1 o co .._, ...... .._, a1 o u "" o .._, 1 g J~ • ~ ..... tJ cG ..... Ul ._, ....... z ..., ., llllllber Station n- ... oo u o:n ...... .._, s :z: s co .._, .._, 11 ., a1 g !l u 11 •

:,N 0 !l : ~ Gl :. & .;: .._, .;: g...... Ill ~ ~ II ~ • ... ;: "I u u I ~ ~~ "&'ci_ ::::;. ~~ ~ .._, § CD § CD ~.J' 6ol ._. ._. 6ol .C ::IU ~ !11 g ;:::u. ;: c: ..: I "':! !: ; ~ g ] t :.; s ~ ~ ;; ] g t ~ ~ ~ ] ~ lib I -e ~ t:!i~ ~ .!::: ... Ill., a ... IC co ... ... co "' o o ,......, ::1 .c .-4 ... .c 11.-4 co co a g ~ z.~ :a ~ - &>. <1> 1>1 o:n,.. U :r: en P.OQ o:n U fao :Z: &>. Clll UU :z: <n e>.U

2108000 Northeut cape Fear River near 600 Oct 19SC daily Max 14 83 17 3 3 33 3 7 4 7 29 52 s 6 9 10 163 92 56 52 267 7 6 200 Ounquapin, N C to Ml.n 1 3 01 2 8 2 7 2 4 8 3 6 o 0 00 32 23 9 2 39 S 1 30

Sept 196 Avq 6 9 25 S 3 1 2 8 6 1 2 14 S 8 14 2 1 6 03 70 48 18 8 8S 89

2108566 Northeast cape Fear River near about Oct 196 duly Max 10 45 10 1 8 21 2 3 29 13 34 3 3 4 86

126 94 30 13 170 1 4 160 Burg•, N C 920 to Ml.n 2 7 00 3 s 1 3 9 6 6 3 2 4 s o 3 00 46 29 12 0 48 6 0 100

~ept 196~ Avq 6 6 18 6 0 1 1 9 1 1 3 lS 7 4 14 1 l l 24 72 59 19 7 87 SS

2108619 Rortheut Cape rear River near about Oct 195~ daily Max 18 1 o 27 2 9 21 4 1 74 16 41 4 4

8 30 138 122 73 18 203 8 3 340 CUUe H&yDe, II C 1500 to Ml.n 2 1 00 3 7 3 2 o 1 8 1 1 4 o o 0 00

1? 29 ll 0 46 S 6 SO ~ept 196 Avq 6 1 23 1 1 1 1 6 3 1 1 19 6 1 9 9 2

1 3 11 76 48 22 8 11 153

- -

mum mtxmg ratto needed to produce parttally mtxed con­ditiOns ts about 0 5 (Refer to dtscusswn on estuarme types m the sectiOn on "General Hydrology ") Based on measurements of ttde-affected flow m the estuary, the mtmmum freshwater mflow needed to produce parttally mtxed condttwns (and, hence net upstream velocities near the channel bottom) would be about 6,500 ft3/s Although freshwater mflows of thts magmtude or greater occur less than 5 percent of the ttme, tt ts posstble that stgmftcant upstream mtgratton of shoaling matenals occurs due to thts phenomenon

The thtrd and posstbly the maJor source of shoaling matenals ts wtthm the estuanne reach Itself These sources could mclude matenals eroded from the shores, matenals resuspended from the channel bottom and moved by ttdal actton to the shoaling areas, and slumpmg of ma­tenals adJacent to the navtgatton channel

Salinity

Vanabons m Time and Space

With respect to salimty, the Northeast Cape Fear Rtver estuary may be classtfied as a well mtxed estuary, for most of the ttme, at least Thts has been venfied by several spectfic conductance surveys, one of whtch IS

summartzed m ftgure 2 17 Thts figure shows hnes of equal spectfic conductance along a channel profile of the Northeast Cape Fear Rtver estuary, based on data col­lected on November 9, 1966 There was very little dtffer­ence on that day between surface and bottom spectftc con­ductances m most of the reach portrayed here The mtxmg mdex was estimated to be about 0 06 for that day, which ts very close to the arbttrary upper limtt of 0 05 for a well mixed estuary Although no extenstve spectfic conduc­tance data were collected wtthm any cross sectiOn on that day, It ts not likely that any stgmftcant spectftc conduc­tance dtfferences existed wtthm cross sectiOns

WATER

\

' \ U\ Q

.c. t ~ ~

' ~ ~ c ~ ~ c 1'1') ... ~ .... <::::) - -\C)

Htstoncally, the maxtmum observed upstream mtru­swn of saline water mto the Northeast Cape Fear estuary occurred dunng Humcane Hazel on October 15, 1954, when chlonde concentratiOns reached I ,450 mg/L at Cas­tle Hayne Based on thts and mformatwn m figure 2 18 (dtscussed later), the saltwater front could have been 2 or 3 mtles upstream from Castle Hayne on that date

The very extreme saltwater encroachment whtch took place due to Humcane Hazel was m addttwn to the extreme encroachment whtch had already taken place due to record low nver flows tmmedtately precedmg the hur­ncane At Chmquapm, for example, the dtscharge aver­aged only 5 3 ft3 Is on October 10-11, I954, the all-ttme low for the 37-year penod of record On October 9 and I 0, I954, chlonde concentrations were already about 500 mg/L at Castle Hayne, the greatest salimty mtruswn of re­cord, up to that ttme The recurrence mterval of two such rare events occurrmg m successiOn IS not known, but tt may be reckoned m centunes

The maxtmum seaward movement of the saltwater front occurs dunng times of htgh freshwater mflow, usu­ally m the spnng At such ttmes, the front may be dis­placed out of the Northeast Cape Fear Rtver estuary al­together, leavmg the estuary completely fresh for a short penod

It ts not economically feastble on a routme basts to survey the entire nver to locate the saltwater front How­ever, based on prevwus salimty surveys, a type curve has been developed for the Northeast Cape Fear Rtver estuary whtch may be used to esttmate the spectftc conductance at any pomt m the estuary, tf the spectfic conductance ts known at only one pomt (ftg 2 18) As an example of the use of thts type curve, suppose that the spectfic conduc­tance near the channel bottom at a htgh slack water IS

6,000 J.Lmhos at Cowpen Landmg, II 2 miles upstream from the U S Htghway I7 bndge m Wtlmmgton, (U S Highway I7 bndge IS about 0 85 mtles upstream from the moqth of the estuary) and we want to know the locatiOn

SURFACE

\ ' I I ~ ~ ~ ~ ~ ~ ~ ~ ~ lc) ~~ lc)

\ ) I CHANNEL \ BOTTOM 11 I I I I I I I I I I

2 3 4 5 6 7 8 9 10 II 12 13 14 15 RIVER MILES UPSTREAM FROM u s 17 BRIDGE AT WILMINGTON

F1gure 2 17. Long1tudmal vanat1ons m specifiC conductance of the Northeast Cape Fear R1ver estuary on November 9, 1966 Depths are vanable and should not be mferred from the sketch

Hydrology of the Cape Fear R1ver Estuarme System 37

/

1-­<(

(f)

~ IO,ooo~--~~--~~~~~-----+-----+----~----~----~----+-----1 u ~

z

-w u z <( t­u ::::> C)

z 0 u

u LJ..

u w a.. (f)

::::!: 0 t---1--0 CD

sooo~--+---~--~+~--+---4---~---+--~----r-~

\ Example 1n text 6 0 00 1------1----+---+----+----+-- -r- - -1-- - -t--,

~ I I ~ I I I \ I

4000 ~-+--+---+--0 -+-rt')-+-l--+~\-+----+----ti---r--------1

:1 ~I ~1 1\ ~1

2000~--~--~----~----~--+----+~~+---~----r---~

I "i'l_l I I I I l I r---

OL---~----~----~--~~--~----~--~----~----~--~ 0 2 3 4 5 6 7 8 9 10

MILES UPSTREAM

F1gure 2.18. Specafac conductance type curve for the Northeast Cape Fear Raver estuary

38 Hydrology of MaJor Estuar1es and Sounds of North Carohna

of the saltwater front (800 JJ.mhos) To determme this, fust find the miles upstream value on the abscissa corres­pondmg to the 6,000 JJ.mho value of the ordmate This value IS 4 3 miles Next, find the abscissa value corres­pondmg to the ordmate value of 800 JJ.mhos This value IS 8 0 miles The distance upstream from the 6,000 JJ.mhos location to the 800 JJ.mhos location IS 8 0-4 3, or 3 7 miles Because Cowpen Landmg Is at the 11 2 nver mile pomt we would expect on that date to find the salt­water front near the channel bottom at the 14 9 nver mile pomt(ll 2+3 7 = 14 9)

Relation of Sahnity to Freshwater Inflow

The relatiOn of sahmty to freshwater mflow to the Northeast Cape Fear River estuary IS more complex than m most estuaries because It IS affected by sahmty condi­tions m the Cape Fear River estuary Nevertheless, such a relatiOn has been developed for the Northeast Cape Fear River estuary, which may be applied with useful accuracy to predict movements of the saltwater front The relatiOn (fig 2 19) IS based on the discharge at the Chmquapm gage and the locatiOn of the saltwater front dunng high slack water as observed dunng SIX sahmty surveys made between August 1 , 1955, and November 9, 1966 Of sev­eral flow parameters tned, the location of the saltwater front durmg htgh slack water related best to the precedmg 21-day average freshwater discharge

The scatter of data pomts m figure 2 19 may be due to several factors One IS that unusually large or small tidal ranges for a gtven day may result m correspondmgly greater or lesser upstream mcursions of sahne water on that day A second IS that the relatiOn IS mfluenced by wmds, which, If blowmg upstream, may result m greater-

z 800 a: c:a: ::> 0 z :I:

u 600 1-c:a:

:s 0 ....J 1..1...

>- 400 c:a: 0

I

~

> 1-::> ~ 200

r\. '\.

'

I

Kl-55 (dole(

' 10-25-62

" ~ ·-21-6: 1

"' 7-23-63 0

5-27-64

than-normal saltwater advances, and, If blowmg down­stream, m lesser saltwater advances

Sahmty conditions m the Cape Fear River estuary are a third factor mfluencmg the scatter of pomts m figure 2 19 If, for example, high flows m the Cape Fear River basm due to a ramstorm occumng m that basm (but not m the Northeast Cape Fear River basm) displaced sahne water downstream further than before the storm, this would also decrease sahmties m the Northeast Cape Fear River basm to some degree A fourth factor mfluencmg the relation takes effect when the position of the saltwater front IS not m eqmhbnum with freshwater mflow This situatiOn may exist when a penod of high freshwater m­flow IS followed Immediately by a penod of much lower freshwater mflow The saltwater front would Immediately begm to move upstream m response to the dimimshed m­flow, but may not reach an eqmhbnum position withm the 21-day penod used m developmg the relatiOn

Regardless of these hmitmg factors, the relation can be used to roughly predict saltwater advances under a wide range of freshwater mflows as measured at Chm­quapm Such mformat10n could be useful, for example, m predictmg whether or not sahne water would reach a water-supply mtake under prevailing mflow conditions It may also be useful m locatmg future freshwater supply m­takes where there IS the least chance of saltwater mtru­ston

For some potential users contemplatmg a water sup­ply m the lower reaches of the Northeast Cape Fear River estuary, a certam degree of nsk of saltwater mtrusion may be acceptable m return for advantages gamed by locatmg near waterborne transportatiOn To help evaluate this nsk, a frequency of mtrus10n relatiOn has been develped and IS shown m figure 2 20 The relatiOn was developed by com-

V)

z 0 u

I

I I

~~ ~

11-9-66 Es 11 mated value

V .l ~H"urr1cane Hazel C\i

0 ~ 0 c:a: a:: ~

> c:a:

II- r- ·-r--- -- 10-9,10-54 rf_ --f--4- - ... 10-15-54

4 6 8 10 12 14 16 18 20 22 24 MILES UPSTREAM FROM US 17 BRIDGE, WILMINGTON, Of THE 200 MILLIGRAMS PER LITER CHLORIDE CONCENTRATION

Figure 2 19 Relat1on of the locat1on of the saltwater front m the Northeast Cape Fear R1ver estuary to the precedmg 21-day average d1scharge at Chmquapm

Hydrology of the Cape Fear River Estuanne System 39

bmmg elements of the flow relat1on m figure 2 13, the 21-day low-flow frequency curve m figure 2 14, and the flow-sahmty relation of f1gure 2 19 As an example of the use of the relatiOn m f1gure 2 20, suppose that 1t was ob­served m one year that the max1mum mtrus10n of the salt-

30

Example 1n text

water front was 18 m1les upstream from the U S Htgh­way 17 bndge m W1lmmgton Accordmg to figure 2 20, we would mterpret that the saltwater front would reach thts far upstream, or farther, only once every 20 years, on the average

,..-.,., . ~-"'" ... . --·

--- --- - -- -r-- -~ 1-----~ ~ c::r ,.._ w­a:: ~· 1-- >­c.nc::r a...3: =>:r: (./)(.!)

w :r: 10 .....J 9

~..,... ... J ............ /.' I

I

8 7

6

5 I 03

,.,~ ........ ,..-

Ill

.~ ./

,_

I 25

..,.,.. v I

I

I I 66 2 2.25 3.33 5 10 20 50 100

RECURRENCE INTERVAL, IN YEARS

F1gure 2.20. Frequency of mtruston of 200 mg/L chlonde for vanous locattons m the Northeast Cape Fear Rtver estuary

3. Hydrology of the Pamlico Sound Estuarine System

For purposes of the report, the Pamhco Sound es­tuarme system (pi 1) mcludes Pamhco Sound, the Neuse­Trent, and Tar-Pamhco nver systems, and all other es­tuarme waters tnbutary to tt Techmcally, thts mcludes Albemarle Sound and tts associated estuanne waters to the north, but because of tts large stze and relatively mmor degree of mteractton wtth Pamhco Sound, the Albemarle Sound estuarme system ts constdered separately m th1s re­port Core Sound to the south drams parttally to Pamhco Sound, but tt ts not tdenttfied wtth the Pamhco Sound sys­tem for present purposes

The Pamhco Sound wtll be dtscussed ftrst because the hydrology of the estuartes opemng mto tt ts mextnca­bly related to the hydrology of the sound Pamhco Sound

40 Hydrology of MaJor Estuanes and Sounds of North Carohna

ts connected wtth the ocean through several relatively small openmgs m the Outer Banks, pnmartly Ocracoke, Hatteras, and Oregon Inlets Thts hmtted access, m com­bmatiOn wtth the broad expanse of the sound, results m ocean tides bemg dampened to less than 0 2 foot, except near the mlets (Roelofs and Bumpus, 1953) However, tidal ranges m the estuanes emptymg mto Pamhco Sound may be as much as a foot m some locations, due to fun­neling effects

A second feature of the Pamhco Sound system ts that, on a short-term basts, wmd-dnven currents are often dommant m both the sound and adJmmng estuanes The large s1ze of Pamhco Sound allows ample opportumty for wmd setup over long fetches Wtthm the estuanes, the veloc1ty of wmd-dnven currents may be mcreased because of funneling effects A second factor whtch contnbutes to the relative Importance of wmd-dnven currents m the sys­tem IS that veloctttes due to freshwater mflow are low Pamhco Sound and tts estuaries are drowned nver valleys Consequently, the nver channels are overstzed for the amount of water they now carry, resultmg m low vel­octttes due to freshwater mflow

In the long term, however, freshwater mflow ts more Important than wmd m affectmg net flow because the effects of wmds blowmg from vanous dtrectwns are noncumulative Thts 1s true throughout the Pamhco Sound estuanne system

The data and mformatwn on whtch these dtscus­smns are based are from varwus sources Plate 1 shows the locatiOn of key flow and water-quahty data-collectiOn stations operated by the Geologtcal Survey wtthm the Pamhco Sound system These stations were used to help defme freshwater mflow, freshwater quahty, and sahmty charactensttcs of the Pamhco Sound system In addttlon to data from these sttes, the Geologtcal Survey has con­ducted a number of spectfic conductance surveys to deter­mme the extent of saltwater mtruswn, most notably s1x surveys of the Tar-Pamhco and Neuse-Trent systems made between September 14, 1954, and June 1, 1955 In addt­tmn to the Geological Survey data, mformatton acqmred by the National Oceamc and Atmosphenc Admtmstratwn, the Offtce of Sea Grant of the Natwnal Sctence Founda­tion, the Umverstty of North Carohna, North Carohna State Umverstty, East Carohna Umverstty, and Woods Hole Oceanographic Institution was utthzed m thts study

PAMLICO SOUND

Pamhco Sound (pl 1) covers an area of about 2,060 mt2 , bounded on the west by the mamland and on the east by the Outer Banks It ts the largest sound formed behmd the hamer beaches along the Atlantic Coast of the Umted States The total volume of water contamed m 1t amounts to about 920 btlhon cubtc feet or about 21 mtlhon acre­feet In contrast to tts great area, the average depth 1s only about 16 feet, and the maxtmum depth ts only 24 feet

Pamhco Sound 1s an Important commercial and sport ftshery, and extensive shallow areas and salt marshes along tts fnnges serve as nursenes for a vanety of commercially and recreahonally Important manne spectes, mcludmg shnmp, oysters, clams, scallops, blue crabs, spot, stnped bass, croaker, and flounder

Pamhco Sound also ts an Important hnk m the At­lantic Intracoastal Waterway Water-related problems m Pamhco Sound mclude occaswnal ftsh ktlls due to anoxtc condttmns, contammatwn of some clam and oyster pro­ducmg areas, property damage due to humcane surge, too-low or too-htgh sahmttes m ftsh nursery areas due to both natural and man-mduced causes, shorehne eroston, and sedtmentatwn m shtppmg channels

The total area drammg dtrectly mto Pamhco Sound ts about 12,520 m12 , mcludmg the area of Pamhco Sound In add1t10n, water from Albemarle Sound and areas tnbutary to 1t (total of 18,360 m12

) enters Pamhco Sound mdtrectly

through the Croatan and Roanoke Sounds Thus, Pamhco Sound receives dramage from a total area of about 30,880 m12 The average freshwater mflow to Pamhco Sound from thts area 1s about 32,000 ft3/s At thts rate, 1t would take about 11 months for the flow volume to equal the volume of the sound The average mflow value accounts for prectptta­twn on and evaporation from the sounds and the wtde open­water areas of the varwus estuanes The average monthly m­flow to Pamhco Sound ranges from about 55,200 ft3/s m February to about 21,000 ft3/s m June

As dtscussed by Folger (1972), Bluff Shoal (fig 3 1) dtvtdes Pamhco Sound mto two broad basms Bottom topog­raphy m the northern area dtps smoothly toward the center to the maxtmum depth of approximately 24 feet In the south­ern part, shoals proJect from the western shore well mto the sound A ttdal delta extends mto the sound from Ocracoke Inlet

Folger notes that fme sand (ftg 3 2) cover~ most ofthe bottom, wtth slit present pnmarlly m the deep areas of the northern basm and m the channels extendmg mto the sound from the mouths of the Neuse and Pamhco Rtvers Medmm sand covers most shoals and extends soundward from mlets as tidal-channel deltas and from the hamer Islands as wash over fans

There 1s a general mcrease m oxtdtzable orgamc mat­ter and orgamc carbon m the bottom sedtments (ftg 3 3) to­ward the center of the northern part of the sound and toward the axes of the Neuse and Pamhco Rtverchannels where, ac­cordmg to Folger, the finer sedtment ts concentrated Most of the orgamc matenal IS apparently due to mdtgenous bwlogtcal achvtty, although he notes that some peat evi­dently underlies a thm veneer of sand at the southern end of the sound

The htghest concentrations of calcmm carbonate (ftg 3 4) m the bottom sedtments are associated wtth the fme sed­Iments m the northern basm and near the nver mouths, and wtth the medmm sands of tidal channel deltas at mlets The calcmm carbonate m these areas 1s mostly shell detntus

Water Budget and Flow

The net freshwater mflow to Pamhco Sound may be determmed by a stmple accountmg of freshwater accordmg to the equat!on

P+~ -E =In (3 I)

where P ts prectpttatwn on the sound, 11 ts freshwater mflow from land dramage, E ts evaporatton from the sound, and In ts net freshwater mflow to the sound (change m storage m the sound ts assumed to be zero) Monthly freshwater budgets were calculated for Pamhco Sound utthzmg equa­tiOn 3 I and these are shown m table 3 I

Hydrology of the Pamhco Sound Estuarme System 41

EXPLANATION

Ocracoke lnle I

-- 12 --Line of equal water depth­

Contour interval 6 teet

10 5 0

10 0

Figure 3.1. Depth of Pamlico Sound. (From Pickett, 1965.)

The major freshwater flow contributors to Pamlico Sound are the Neuse-Trent River system (average flow-6, 100 ft 3/s from 5,598 m?) and the Tar-Pamlico River sys­tem (average flow-5,400 ft3/s from 4,300 mi 2

). Indirectly, two other major rivers, the Roanoke (average flow-8,900 ft3/s from 9,666 mi 2

) and the Chowan (average flow---4,600 ft3/s from 4,943 mi 2

) drain into Pamlico Sound through Al­bemarle Sound. The monthly values for these rivers and other contributing areas were determined on the basis of dis­charge records at gaged locations, adjusted for ungaged areas .

42 Hydrology of Major Estuaries and Sounds of North Carolina

10

10

In let

\ " \

20MILES EXPLANATION

20 30 KILOMETERS -Coarse son d

~ Medium so nd

D Fine-very tine sand

o S i It

Figure 3.2. Texture of bottom sediments in Pamlico Sound. (From Folger, 1972, after Pickett, 1965.)

Precipitation values for Pamlico Sound and adjacent open-water areas (2,064 mi2

) were determined by averaging National Weather Service station records at New Bern, New Holland, and Cape Hatteras . Precipitation on Albemarle Sound and adjacent open-water areas (934 mi 2

)

was determined from monthly average values from Na­tional Weather Service stations at Elizabeth City, Manteo, and Plymouth. Evaporation values were derived for all major open-water areas by applying a coefficient of 0. 7 to monthly values of the Maysville pan evaporation station of the National Weather Service. Precipitation and evap-

EXPLANATION 10 5 0

PERCENT ORGANIC MATTER 10 0 10

0 0-1 CJ 1-2 k2Zj 2-4 -4-8

Figure 3.3. Oxidizable organic matter and organic carbon content of bottom sediments in Pamlico Sound. (Oxidizable organic matter data are from Pic­kett, 1965; organic carbon data are from Hathaway, 1971.)

oration values for Albemarle Sound, though not shown in table 3. I, are reflected in the inflow values from Al­bemarle Sound.

It is interesting to note from table 3. I that minimum net inflows to Pamlico Sound do not clearly occur in Sep­tember, October, and November, as is the case with many natural streams in North Carolina. Actually, minimum net inflows seem to occur in June, when evaporation rates are the greatest.

As is often the case, extreme and unusual events are of greater interest than normal events. It is useful to

10

Inlet

\ ~

\

20 MILES EXPLANATION

20 30 KILOMETERS PERCENT Caco 3

0 o-2 ~ 2-4 ~ 4-8 §8-16 ->16

Figure 3.4. Calcium carbonate content of bottom sediments in Pamlico Sound. (From Pickett, 1965.)

speculate on what net inflows would be, say, in a month with little or no rainfall occurring during the low-flow period of June-October. In such a situation, freshwater in­flow from land drainage would be minimal (say at the 30-day, 1 0-year minimum flow range) and evaporation would be, if anything, somewhat greater than normal for such a month because incident solar radiation would be greater due to lessened cloud cover. Figure 3.5 shows low-flow frequency curves for 7- and 30-day periods for all inflow due to contributions from land areas draining directly or indirectly into Pamlico Sound. The minimum 30-consecu-

Hydrology of the Pamlico Sound Estuarine System 43

~ ~

:X -< Q.

Q

~ a ~ Ill 0 .. m ~ c ~ ~ Ill ::I Q.

g ::I

9-a z 0 :::l :r (;/ 2. 5 Ill

Drainage

Element of Gross water budget area in square miles

Precipitation on Pamlico Sound 2,060

Evaporation from Pamlico Sound 2,060

Freshwater inflow to Pamlico Sound from land areas 10,460 tributary to Pamlico Sound

Inflow from Albemarle Sound 18,360 to Pamlico Sound

Net inflow to Pamlico Sound 30,880 (or outflow to the ocean)

!/Rounded·

Table 3.1. Monthly and annual gross water budget for Pamhco Sound

Average monthly and annual values, in cubic feet per second

Average! Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. annual

I

6,780 7,930 6,620 5,380 6,590 9,340 12,600 12,100 10,800 6,710 7,080 7,040 8,250

2,330 3,310 4,900 7,530 8,590 9,320 10,000 7,680 6,110 4,080 3,000 1,990 5,740

17,000 21,600 19,100 13,200 11,300 6,220 8,940 10,900 8,530 7,900 &,240 11,100 12,000

22,800 28,300 25,000 21,300 15,500 12,200 14,200 14,700 13,100 10,700 13,300 15,600 17,200

44,200 54,500 45,800 32,400 24,800 18,400 25,700 30,000 25,300 21,200 26,600 31,800 31,700

6000 0

'I\. :z 0 u w 5000 (f)

'""" "'3o ~~

a:: w Cl...

4000

"' ....._ w w LL.

u 3000 D 4y'·~,l~. CD

::::> u

z

w (!)

a:: <! I u (f)

0

2000

1000

0

~ r---~ ~ r--o __ ~0

Drornage area rs 27,518 mr 2

0 01 II 15 2 3 4 5 10 20 30 40 50 100

RECURRENCE INTERVAL, IN YEARS

F1gure 3.5 Magmtude and frequency of annual mmrmum 7- and 30-consecutrve-day average mflow to Pamlrco Sound from drrect and mdrrect land dramage, not adjusted for precrprtatron on and evaporatron from Pamlrco and Albemarle Sounds and assocrated open-water areas

tive-day 10-year dtscharge denved from tt ts about 3,000 ft3/s If we assume that thts mflow occurs m June, when evaporation ts at a maxtmum (about 15,300 ft3/s for Al­bemarle Sound, Pamltco Sound, and assoctated open­water areas), and tf we further assume that dtrect precipi­tatiOn on the sounds and assoctated open water areas IS

zero, then net freshwater mflow to Pamhco Sound, Al­bemarle Sound, and assoctated areas from equation 3 I would be (0 + 3,000 - 15,300) ft3/s, or - 12,300 ft3/s In other words, the rate of loss of freshwater from the sounds and associated areas by evaporation would exceed gams from land dramage and prectpttatiOn by about 32 btllton ft3 Of course, these evaporattve losses would be made up by seawater entenng Pamhco Sound through the ocean mlets, thus mcreasmg the sahmty of the Sound

Htgh flow penods are also of great mterest because the greater part of annual flow volumes occur durmg rela­ttvely short ttme penods and this ts when most of the flushmg of pollutants and sahne water takes place By m­specttOn of table 3 I , tt ts seen that the htghest mflows generally occur from January-Apnl, rangmg from an av­erage of 54,500 fe/s m February to about 32,400 ft3/s m Apnl Figure 3 6 shows high-flow frequency curves of m­flow from dtrect and tndtrect land dramage mto Pamhco Sound for 7- and 30-day penods As an example to con-

trast wtth the mmtmum 30-consecuttve-day I 0-year aver­age flow of 3,000 ft3/s, the maximum 30-consecuttve-day I 0-year average flow from ftgure 3 6 IS about I 06,000 ft3/

s, about 35 times as great If this mflow were to occur m February, when the excess of prectpttatiOn over evapora­tiOn ts, on average, eqmvalent to an addtttonal mflow of about 5,200 ft3/s, then the net mflow (or outflow) would be about Ill ,000 ft3/s, or an eqmvalent volume of about 269 mtlhon ft3 (29 percent of the volume of Pamhco Sound) At thts rate, m a penod of 14 weeks the water reachmg the sound would equal the volume m storage, m contrast to the II months needed for average freshwater mflow to reach thts volume

Discharges and resultant velocities due to freshwater flow mto and out of Pamltco Sound are of small mag­mtude and usually overshadowed at any gtven moment by flows and vel oct ties due to wmds and/or ttdes However, net flows due to tides and wmds tend to approach zero over ttme, so that long-term average net flows at any pomt may be ascnbed pnmanly to freshwater mflow Con­sequently, flows due to freshwater mflow may have value m studtes of long-term net transport of pollutants and nu­tnents mto and out of Pamltco Sound

An tdea of the magmtude of ttdal exchange between the ocean and Pamltco Sound may be obtamed from table

Hydrology of the Pamhco Sound Estuanne System 45

400,000

Dramage area 1s 27, 518 m1 2

0 2 0 u w 300,000 (./)

a:: w a_

....... w w u...

u 200,000

~· --~---+--~------~

CD ::::> u

2

w <..!)

a:: 100,000 I <( -:r: u (./)

-0

OL------L------~----~----L-~--~------~------~--~~~~----~ I 01 I I 15 2 3 4 5 10 20 30 40 50 100

RECURRENCE INTERVAL, IN YEARS

Figure 3.6. Magnatude and frequency of annual max1mum 7- and 30-consecutlve-day average mflow to Pamllco Sound from d1rect and md1rect land dramage, not adJusted for prec1p1tat1on on and evaporation from Pamllco and Albemarle Sounds and associated open-water areas The total area not adJUSted for 1s 3,362 square miles of the total dramage area of Pamllco Sound of 30,880 square m1les

3 2, which mdicates that combmed maximum flood or ebb flows through Oregon, Hatteras, and Ocracoke Inlets may be on the order of 600,000 ft3/s, far more than the net out­flow of about 32,000 ft3/s due to freshwater mflow Al­though total volumes associated wtth ebb flows (table 3 2) exceed over time those associated wtth flood flows, m the case of almost half of the mdtvidual measurements m table 3 2, the volumes associated wtth flood flows exceed those associated with the precedmg or followmg ebbs It may be that some or even all of these apparent mcidents of mdtvidual flood volumes exceedmg ebb volumes could be accounted for by measurement error or dmmal m­equahties m tides, but JUSt as hkely the exceedances were real and caused by easterly wmds prevailing dunng or be­fore the measurements It IS also worthy of note that maximum flow rates occurred dunng flood tide m the maJonty of measurements, even m some cases where total ebb volumes exceeded those for floods

Table 3 3 gtves predicted tide ranges and maximum currents for several locatiOns at or near the mlets The lo­catiOns of these mlets are shown m plate 1 The predicted

46 Hydrology of MaJOr Estuar.es and Sounds of North Carohna

mean tidal ranges at the mlets are all stmtlar, from 1 9 to 2 0 feet, though they are less than m the adJacent ocean, where predicted ttde ranges vary from 3 2 feet at Kttty Hawk to 3 4 feet at Hatteras It Is mterestmg to note from companson of the Ocracoke Inlet and Ocracoke statiOns how qmckly tides damp out away from the mlets At Oc­racoke Inlet, the mean predicted tidal range IS 1 9 feet, whtle at Ocracoke, located m Pamhco Sound only about 4 8 mtles northeast of the mlet statiOn, mean ranges are nearly halved to 1 0 foot

Of course, tide predictiOns are made on the basts of an analysts of predictable mutual gravitatiOn forces of the Sun, Moon, and Earth, and actual ttde heights and cur­rents m Pamhco Sound often dtffer from predictiOns, pnmanly because of the unpredictable effects of wmds Detailed consideratiOn of the complex effects of wmds on circulation m Pamhco Sound IS beyond the scope of this report, but several reports, mcludmg Smger and Knowles (1975) and Knowles (1975) discuss the effects of wmds and tides on ctrculatton at several locatiOns m and near Pamhco Sound

Table 3 2 T1dal flow and related data for Oregon, Hatteras, and Ocracoke Inlets Except for measurements made m Apnl1950, by Roelofs and Bumpus and on June 28, 1973, by Smger and Knowles, the measurements are from records of the U S Army Corps of Engmeers

Cross Maximum Total Flow section rate of flow Date

(ft 2 ) (ft 3 /s) (acre-ft.)

at mlw Flood Ebb Flood Ebb

I Oregon Inlet

Sept. 9, 1931 39,000 134,100 88,200 47,800 37,400 Aug. 31, 1932 129,100 102,700 42,700 40,100 Oct. 11, 1932 126,500 127,300 34,900 57,200 Aug. 24, 1937 44,400 180,000 142,000 63,500 55,900 Aug. 14, 1939 56,000 152,000 141,000 37,800 71,500 Apr. 23, 1950 28,000 90,000 38,200 Sept.27, 1965 66,800 292,000 145,800 98,200 54,200 June 28, 1973 G8,800 171,000 146,000

Hatteras Inlet

Apr. 25, 1950 52,700

Ocracoke Inlet

Apr. 27, 1950 82,800 45,400 122,000 May 25, 1958 107,500 285,000 78,400 May 25, 1958 96,100 273,000 104,000 Oct. 14, 1962 94,100 329,000 125,000 Oct. 14, 1962 74,400 344,000 129,000

Table 3.3. Pred1cted t1de ranges and max1mum currents for locations at or near mlets to Paml1co Sound From Nat1onal Ocean SurveyT1dal Current Tables and T1de Tables for 1977

Tidal ranges Average maximum currents Location in feet per second in feet

Average Average

Lat. Long. spring flood ebb mean velocitv velocity

Oregon Inlet 35°46' 75°32' 2.0 2.4

Hatteras Inlet 35°12' 75°44' 2.0 2.4 3.6 3.4

Ocracoke Inlet 35°04' 76°01' 1.9 2.3 2.9 4.0

Ocracoke, Ocracoke Inlet 35°07' 75°59' 1.0 1.2

Hydrology of the Pamhco Sound Estuarme System 47

Water Levels

The greatest water level fluctuatiOns m Pamlico Sound occur dunng hurricanes, when land areas 10 to 15 feet above mean sea level are sometimes mundated, caus­mg great damage to bmldmgs and croplands adjacent to the sound Ftgure 3 7 shows water level conftguratwns dunng Hurricane Donna at 0200 and 0500 hours on Sep­tember 12, 1960 These contours were sketched by the U S Army Corps of Engmeers from ttde gage records and appeared m the 1961 publicatiOn "Report on the troptcal hurricane of September 1960 (Donna) " They Illustrate not only the wtde vanatwns m stage whtch may extst from place to place at a gtven ttme, but also the great fluctua­tions whtch may occur at a gtven place m a relatively short penod of time dunng hurricanes It ts Important to note that the datum for ftgure 3 7 IS 4 0 feet below sea level, thus, for example, a water level contour of I 0 foot m figure 3 7 ts actually 3 0 feet below sea level

An Important tool for gagmg potential flood losses from wmds ts knowledge of the frequency of floodmg 1

"PredictiOn of the frequency with whtch a given locality ts likely to be flooded with water from the estuanes or sounds ts mexact because of the almost mftmte number of possible combmatwns of wmd directiOn and veloctty, shoreline configuratiOn, fetch, and the amount of vegeta­tion and manmade structures that might Impede free ad­vancement of a wave Some Idea of the seventy of the problem can be obtamed from figure 3 8, on which are delineated approximate boundanes of wmd-tide floods likely to be equaled or exceeded 50 percent of the years and 1 percent of the years By 'exceeded' we mean that mundatton of an area at least as great as that shown ts likely every other year on the average at the 50-percent probability, and once every hundred years on the average at 1-percent probability These are average frequencies over long penods of time, and no specific time mterval between two consecutive events Is Implied * * * How­ever, all of the area wtth an equal chance of bemg flooded at a given frequency wtll seldom, If ever, be flooded by the same storm For example, strong southerly wmds cause mundatwn along northern shorelines of a body of water, but might actually lower water levels along the southern shorelines

"It IS Important also to qualify the accuracy of fig­ure 3 8 The boundary outlinmg the area mundated by a flood with a 1-percent chance of exceedance was transfer­red directly from flood-prone area maps available from the U S Geological Survey The hnes m figure 3 8 are gen­eral and are not as detailed as those appeanng on the large-scale flood-prone maps These small-scale tllustra-

1The remamder of this section IS quoted directly from Wilder and others ( 1978) The figure numbers have been changed to correspond to those m this report

48 Hydrology of MaJor Estuaries and Sounds of North Carohna

tions were prepared only to pomt out the potential flood problem If more accurate data are desired, the large-scale flood-prone maps prepared by the Geological Survey and flood-plam mformatton studtes completed by the U S Army Corps of Engmeers should be used Generally the flood with a 50-percent chance of exceedance was sketched on the large scale flood-prone area maps usmg a flood stage from 2 5 to 3 5 ft below the flood outlined as havmg a 1-percent chance of exceedance and then transferred directly to the smaller scale maps of figure 3 8

"Because most of the areas adjacent to the shorelines presently contam dense vegetation or manmade structures, these sources of tidal-floodmg mformatwn, all of whtch consider only wave height and land elevatiOn, may tend to overestimate the extent of mundatwn "

Water Quality

Marshall ( 1951) pomted out the lack of data on water chemistry other than salimty m the open parts of Pamhco Sound and suggested this as an Important area of study His statement remams largely true today, although some valuable data have been and are bemg collected by vanous agencies, mcludmg the Umversity of North Carolina Institute of Marme Sciences (summanzed m Wit­hams and others, 1967) and the North Carolina Depart­ment of Natural Resources and Commumty Development However, much of these data were collected along the fnnges of the Sound, not m the central part The U S Geological Survey has collected chemical data for many years at vanous locations on nvers tnbutary to Pamhco Sound These data Will be discussed m later sections, but extrapolation of this mformation to mfer water quahty of Pamhco Sound would be very difficult for two pnmary reasons Ftrst, of course, Pamlico Sound water IS every­where at all times at least partially mixed with ocean water The second pnmary reason IS that some chemical constituents, such as mtrate (N03) and phosphate (P04),

are nonconservattve and contmue to mteract chemically and biochemically With other substances or orgamsms m the water as the water moves mto Pamlico Sound and, ul­timately, mto the Atlantic Ocean The Pamhco River es­tuary, for example, acts as a trap for phosphate and mtrate dunng algal blooms, which occur there each late wmter or early spnng and each summer (Hobbie, 1974, p 2) The algae trap and utilize phosphorous and mtrogen for growth, then die and settle to the nver bottom Thus, phosphate and mtrate concentrations m the nver water may be much decreased by the time the water reaches Pamhco Sound

Woods ( 1967) collected data on water quahty at sev­eral sites m southern Pamlico Sound from June 1963-0c­tober 1966 (fig 3 9) At 1-month mtervals at each site, vert1-

35

EXPLANATION

Water level contours, 1n feet, September 12, 1960

2 0200 hours

-- 3- -osoo hours

Contour 1ntervol I 0 foot

Mean low water IS -4 0 feet

0 I 0

5 I

5 10

10 ,•

20

N

Cope Hatteras

~ A N 0 c

20 MILES I I

30 KILOMETERS

F1gure 3.7 Estimated water levels m Paml1co Sound at 0200 and 0500 hours on September 12, 1960, dunng Hurncane Donna (FromAmemandA1ran, 1976,afterU S ArmyCorpsofEngmeers, 1961)

Hydrology of the Pamhco Sound Estuarme System 49

1:) 0 10 (I') ~0 M IL ( S

I '--f- L< j ---, .1.,-----,1- T-~ 1Q 20 30 40 "'.0 li" IL t.I [TfP$

Figure 3.8. Areas subject to flood inundation caused by wind tides having A, 50 percent chance of being equaled or ex­ceeded in any one year and 8, 1 percent chance of being equaled or exceeded in any one year. (After Wilder and others, 1978.)

cal salinity and temperature measurements were made at 1-meter intervals and surface and bottom samples were analyzed for dissolved oxygen, plant pigment concentra­tions, and total phosphate. In his report, Woods indicated that both phosphorous and nitrogen are often present in high­enough concentrations in western Pamlico Sound to support algal blooms. It appears that the availability of nutrients is not a limiting factor in determining whether or not algal blooms may occur in western Pamlico Sound.

Dissolved oxygen concentrations in Pamlico Sound ranged from 4 to II mg/L through the course of Woods' study. As would be expected, the highest values occurred when water was cold and the lowest values when water was warmer. In terms of percentage saturation, concentrations seldom went below 50 to 60 percent and during the winter months were normally close to 100 percent. Surface dissol­ved oxygen in Pamlico Sound varied little from place to place at any one time and vertical differences in the sound were slight, even when total oxygen depletion was noted at some bottom stations upstream in the Pamlico River estuary.

50 Hydrology of Major Estuaries and Sounds of North Carolina

Many observers have noted that water temperatures in Pamlico Sound follow air temperatures closely but with some lag. Highest temperatures typically occur during late June, July, and August and lowest temperatures occur during the winter months (fig. 3.10A). Figure 3.108 shows the relation between average surface temperature in the open sound and air temperature recorded by the N a­tiona] Weather Service at Hatteras. The air temperatures used in the graph represent the average of the mean tem­peratures on the day of water temperature observations and the previous day. This was done to allow for the time lag between air and water temperature. Roelofs and Bum­pus found the correlation coefficient between mean water temperature and air temperature to be 0. 972, which is highly significant.

Thermal stratification in the open sound is slight year-round; surface-to-bottom differences rarely exceed 1 or 2° C. Areal differences are likewise small, rarely ex­ceeding 3 or 4° C at any one time. Apparently, winds are effective in promoting vertical mixing throughout the rela­tively shallow depths of the sound.

• /Hotteros , Inlet • ~ Ocracoke Inlet

I?

/ EXPLANATION

• Sampl1ng stat1on

0 5 10 20 30 MILES I I I I I

0 10 20 30 40 KILOMETERS

f•gure 3.9. Samplmg stat1ons used m Pamhco Sound study by Woods (1967)

Hydrology of the Pamlico Sound Estuarme System 51

(f)

W::::::> (..)-

c:x:c.n 30 LL.......J

a:::W ::::::>(..) (f)

(f)

a:::w ww 20 ._a:: <{(.!)

3:~

>-2 .....J-

10 :I: 1-- w-2a::: 0::::::> ~~---

<{

a:: 0 2w <X:CL J F M A M J J A s 0 N 0 J w~ ~w 30

1-- I I I I I I

8 • • (f) ••• ::::::> • • (f)

25 •• • • .....J r- -w (..) •• • • •• • (f)

w • w 20 - • • -a:: (.!) • w • Cl

• • 2 • • 15 - • -•

w • • a:: • ::::::> • • ...._ • • <{ 10 ~ -a:: • w CL ~ w • • • • ...._

5 r- -a::

• <{ • •

0 I I I I I I

0 5 10 15 20 25 30 WATER SURFACE TEMPERATURE I IN DEGREES CELSIUS

52 Hydrology of MaJor Estuar1es and Sounds of North Carohna

Salinity

Ftgures 3 II and 3 12 show the average surface sa­hmty of waters of the Pamhco Sound system for the months of Apnl and December, based on sahmty data col­lected between 1948 and 1966 at a number of fixed loca­tiOns m the system Apnl, on average, IS the month of lowest sahmttes and December ts the month of greatest sahmttes The Apnl-December dtfferences are less at the ocean mlets (~2 grams per ktlogram) than they are near the mouths of the maJor estuaries where the Apnl-De­cember dtfferences may be 4-5 grams per ktlogram The effect of htgh freshwater mflows dunng the late wmter and spnng months from the Albemarle Sound dramage and the Neuse-Trent and Tar-Pamhco nver systems may be seen m the way the htgh-sahmty water has been "pushed" further out mto Pamhco Sound m Apnl as com­pared to December Actually, maximum net outflows occur, on average, not m Apnl but m February, and mmt­mum outflows occur, on average, not m December but m June or October Thts lag m sahmty response to changmg outflows IS due to the large volume of Pamhco Sound and the long ttme reqmred to flush water out of the sound Thus, the sahmty dtstnbutiOn wtthm the sound dunng any one month ts due, not only to flows dunng that month, but to the flows dunng the Immediately precedmg months

Just as wmds are the dommant mfluence on the short-term circulatiOn of water m Pamhco Sound, they are also the dommant short-term mfluence on sahmty dtstnbu­ttons It has been generally observed that easterly wmds cause mcreasmg sahmttes m the sound and westerly wmds cause decreasmg sahmttes However, wtth regard to the effects of northerly and southerly wmds, there ts some confusiOn Most observers agree that northerly wmds wtll cause lower sahmttes m the northern part of Pamhco Sound as fresher water ts pushed mto thts area from Al­bemarle Sound They also agree that southerly wmds wtll cause htgher sahmttes m the northern part of Pamhco Sound as htghly salme water from Hatteras and Ocracoke mlets IS dnven northward It ts the effect of northerly and southerly wmds m southern Pamhco Sound that has been dtsputed Wmslow (1889) reported that southerly wmds wtll cause decreasmg denstttes (sahmttes) m the southern part of Pamhco Sound and Core Sound and northerly wmds wtll cause mcreasmg sahmttes there However, Roelofs and Bumpus ( 1953) observed decreasmg sahmties m Core Sound dunng northerly wmds as fresher Pamhco Sound water was "blown" mto Core Sound More study ts needed to resolve these observational dtfferences, but

Whalebone Inlet, now closed, was open dunng Wmslow's 1889 observatiOns, and Drum Inlet, now open, was then closed Thts would argue for acceptmg the more recent observations by Roelofs and Bumpus Also It IS probably too stmphsttc to say that htgher sahmty waters wtll always prevail at a gtven location wtth wmds from a gtven dtrec­tiOn The wmd speed and Its duratiOn are also Important factors Wmds whtch have prevailed need also to be con­stdered For example, reversal m sahmty trends may occur at a gtven locatiOn tf wmd has prevatled m a gtven dtrectiOn for more than, say, 24 hours, owmg to water bmldup on one stde of the sound creatmg a return flow SituatiOn (Smger and Knowles, 1975)

Sahmty strattftcatton m the open sound IS usually shght, only 0 50 to 1 0 percent greater at the bottom than at the surface (Woods, 1967) Roelofs and Bumpus (1953) gtve the average dtfference m surface and bottom sahmttes as only 0 66 percent, thts small dtfference they attnbute to effecttve mtxmg by the wmds throughout the shallow open-sound depths Woods dtd observe larger open-sound surface-to-bottom sahmty mcreases of as much as 6 percent from the surface to the bottom m 1964 dunng the spnng, summer, and fall Woods thought that thts stratification was due to mcreased freshwater mflows from the Neuse and Pamhco Rtvers whtch occurred ap­proximately four to seven weeks pnor to the observed stratification m the open sound

Magnuson ( 1967) mdtcated that sahmttes m parts of natural or manmade channels connectmg to the mlets may be appreciably greater than sahmttes m adJacent shallower areas However, thts ts partly speculative and needs better confirmatiOn from data

The dtstnbutiOn of many aquatic orgamsms m Pam­hco Sound and tts estuanes and saltmarsh fnnges IS mflu­enced greatly by sahmty patterns Some aquattc orgamsms can tolerate wtde sahmty ranges from almost fresh to al­most sea water (Thayer, 1975, p 64) Others can hve and reproduce only wtthm narrow ranges, sttll others re­qmre dtfferent sahmty condttiOns at dtfferent stages of thetr hfe cycles Thus, any modtftcatiOns by man m the amount and annual dtstnbutiOn of freshwater mflow or m alteratiOn of sahmty patterns wtll exert some control on the plant and ammal populations m Pamhco Sound and adJmmng areas The effects of upstream reservOirs (such as the Falls of the Neuse reservmr), the effects of land clearmg on freshwater runoff (such as ts currently takmg place on the Albemarle-Pamhco penmsula), and the ef­fects of creatmg new ocean mlets and navtgat10n channels should all be carefully evaluated with regard to sahmty constderattons

--c F1gure 3.10 A Mean monthly water surface temperature of Pamllco Sound B Relat1on between water surface temperature of Pamllco Sound and a1r temperature at Hatteras (Adapted from Roelofs and Bumpus, 1953 )

Hydrology of the Pamhco Sound Estuarme System 53

W1ndsor #

10 0

I I t I I 10 0

\

• \

10 20 30 MILES

,' '•

0

E. A t

10 20 30 40 SO KILOMETERS

EXPlANATION

-I 9 - SALINITY, IN GRAMS PER KILOGRAM (Seawater contains about 34 5 grams of dissolved solids per lalogram ) Contour mterva! vanable

Figure 3.11. Average surface sallmty of water m Pamllco Sound and v1cm1ty for the month of Apnl (Mod1f1ed from Williams and others, 1967 )

54 Hydrology of MaJor Estuaries and Sounds of North Carohna

\

,rrt, ' ,, """'- ~W•ndsor

' \ _. \ ·~. I

1 ) .r' Plttlpsl' _f ;.., V · Luit

,-~ Wtfltomston J 0 , Pungo •

~- ; LOkh.__ L ' '"' ~ . \-:;;:;;-- -\ ,_,....., ·~...,. ,~~~ol

10 0

I a ~ I 1 '

10 0

10

10 20

20 I

30 40

EXPLANATION

0

\

~0 KILOt!IETERS

-19- SALINITY, IN GRAMS PER KILOGRAM (Seawater contatns about 34 5 grams of diSSolved sobds per kilogram ) Contour mterval vanable

Fegure 3.12. Average surface salm1ty of water m Pamllco Sound and v1C1n1ty for the month of De­'cember (Adapted from Williams and others, 1967 )

Hydrology of the Pamhco Sound Estuarene System 55

THE NEUSE-TRENT RIVER SYSTEM

The Neuse RIVer (pi 1) ongmates m Durham County, N C , at the confluence of the Eno and Flat RIV­ers m the hilly Piedmont Provmce The nver flows south­east, enters the Coastal Plam near Smithfield, and empties mto Pamhco Sound at Maw Pomt The total length of the mam stem of the nver IS about 250 miles, and Its dramage area IS approximately 5,600 mi2

, which IS about 11 per­cent of the total area of North Carolina The average an­nual precipitation ranges from near 45 mches m Durham County to about 54 mches at New Bern The mean annual flow measured at the most downstream gagmg statiOn, at

' 3 Kmston (station 02089500 on pi 1), ts about 2,900 ft /s for a dramage area of 2,690 mt2

The Trent River ongmates m Lenmr County, N C , and flows almost due east to tts confluence wtth the Neuse Rtver at New Bern Thts JUncture ts about 38 mtles up­stream from the mouth of the Neuse Rtver at Maw Pomt on Pamhco Sound The Trent dramage area of 516 mt2 ts mcluded m the 5,600 mt2 dramage area of the Neuse Rtver The total length of the Trent Rtver ts about 80 miles and the mean annual flow at the gagmg statiOn at Trenton (sta 02092500 m pi 1) ts about 200 ft3/s for a dramage area of 168 mt2

The estimated average annual discharge mto Pam­hco Sound at the mouth of the Neuse Rtver (pi 1) from the enttre 5,600 mt2 dramage area of the Neuse-Trent Rtver system ts about 6,100 ft3/s The estimated average monthly dtscharges at the mouth, m cubtc feet per second, are as follows

January 8,400 July 5,000 February 11,000 August 5,300 March 10,000 September . 5,000 April 7,700 October 3,800 May 4,200 November 3,800 June 3,400 December 5,800

The upstream hmtt of ttde effects m the Neuse and Trent Rtvers has not been well established, but ts thought to be near Fort Barnwell on the Neuse Rtver (about 65 mtles upstream from the mouth at Maw Pomt), on the Trent Rtver the upstream hmtt of ttde effects ts thought to be about halfway between Pollocksville and Trenton, or about 35 mtles upstream from Its mouth at New Bern (about 73 miles upstream from the mouth of the Neuse Rtver)

The Neuse River estuary vartes from 6 3 miles wide and an average depth of 17 feet at Its mouth near Maw Pomt to a width of about 0 9 mile and an average depth of about 8 feet at New Bern From New Bern to the head of ttde near Fort Barnwell, the estuary narrows consider­ably and maximum depths are at least 3 feet m any cross section

56 Hydrology of MaJor Estuar1es and Sounds of North Carohna

The Trent Rtver estuary vanes from 0 3 mile wtde and about 10 feet deep at the mouth at New Bern to about 50 feet wide and 4 feet deep at the head of tide near Pol­locksville

Effects of Wind on Water Levels and Specific Conductance

Water levels m the lower parts of the Neuse River and Trent River estuanes are pnmanly controlled by the directiOn and magmtude of the surface wmds on Pamhco Sound Because of the dampemng effect of Pamhco Sound, ttdal ranges are less than a foot at New Bern Var­Iations m water levels due to freshwater mflow are also small because the surface areas of the lower parts of these estuanes are large relative to freshwater mflow

Figure 3 13 IS a wmd diagram for resolvmg a given wmd to the directional component that IS effective m caus­mg a change m water level at New Bern The values on the circle are based on the cosme of the angle between the actual directiOn of the wmd and the directiOn that causes the maximum effect W mds blowmg m the directiOn of the lower channel axis of the Neuse River (the lower 15 miles) have the greatest effect on the level of water m the estuary This axis of maximum wmd effect forms an angle of 60° with true north Thus, a wmd blowmg from due north (cos 60°=0 5) IS only half as effective m producmg high water levels at New Bern as a wmd that blows from 60° east

77 w-- 87

94 98

0 50 34 17

I s

87 77

64

---E

fagure 3.13. Wmd d1agram for the Neuse R1ver estuary at New Bern See text for explanation

Ftgure 3 14 ts a curve that relates the wmd compo­nent to the change m water level at New Bern The curve shown was developed from Geo1ogtcal Survey water level records of the Neuse Rtver at New Bern and wmd speed and dtrecttOn records from the N attonal Weather Servtce statiOn at New Bern Thts relatiOn mtght be used as a rough predtctor of potential hurrtcane floodmg and m as­stgmng flood nsks to streambank areas To predtct water level changes m the Neuse estuary at New Bern resultmg from wmds actmg on Pamhco Sound, determme the dtrec­ttOn of the wmd, then multtply tts veloctty by the cosme of the angle formed between the actual wmd dtrecttOn and the dtrecttOn of maxtmum effect, obtamed from ftgure 3 13 The result ts the wmd veloctty component Then enter ftgure 3 14 wtth the wmd veloctty component and read the change m water level on the absctssa

Example A 30-mt/hr wmd from the east From figure 3 13, cos me of angle between actual wmd direc­

tion and dtrecttOn of maxtmum effect (30 degrees) 0 87

Therefore, 0 87 x 30 = 26 mtlhr And from figure 3 14, water level change= 4 6ft nse

The htghest recorded water levels at New Bern have been caused by a combmatton of hum cane wmds, the as­soctated low barometnc pressure, and mtense short-term ramfall Humcane lone (September 19, 1955) passed about 15 mtles east of New Bern on a northerly course and caused water levels to nse 10 6 feet above sea level for a short penod The maxtmum wmd recorded near New Bern then was 1 07 mt/hr, the lowest barometric pressure was 27 7 m-

-Cl (/) w a: w :::> Q.. 0 (/) :r:

30

0 a: z w 3= Q.. 20

w (/)

> w ....J

t; ~ 10 w ~2 w

2 4 WATER LEVEL

6 8 CHANGE, IN

10 FEET

F1gure 3.14 Change m water level of the Neuse R1ver es­tuary at New Bern due to wmd as recorded at New Bern Air­port

ches, and over 13 mches of ram were recorded at New Bern At least four other hurrtcanes smce 1913 have caused water levels to exceed seven feet above sea level

An example of the general effect of wmd on water levels and saltwater mtrus10n at New Bern ts shown m figure 3 15 Dunng most of the penod from January 22 through 29, 1965, wmds were blowmg generally from the south and west, the wmd dtrecttOns that tend to lower the water level of the estuary Salty water from Pamhco Sound, whtch had previOusly mtruded up the estuary beyond New Bern, was flushed downstream, as mdtcated by the drasttc dechne m spectfic conducttvtty on January 23 The conducttvtty re­mamed low unttl January 28 when a short-hved dechne m wmd speed permttted salty water to agam mtrude past New Bern The salty water was agam flushed on January 29 when southeast wmds arose, but the saltwater was tmmedtately forced back up the estuary when the wmd shtfted to the north­east and htgh-water wmds blew on January 30

Water Quality

The chemtcal quahty of the freshwater entenng the estuanes from upstream ts, where not contammated, of acceptable quahty for pubhc and mdustnal use wtth a mmtmum of treatment Table 3 4 shows the maxtmum, mmtmum, and average of dtssolved mmeral constttuents from a stte on each nver upstream from any saltwater con­tammatton Generally, maxtmum concentratiOns reflect the quahty of the ground water entenng each nver and mtmmum concentratiOns are more reflecttve of surface runoff The mam dtfference m water quahty between the two nvers ts that concentrations of most dtssolved con­stituents for the Neuse Rtver average stgmficantly more than those for the Trent Rtver The maJor exceptiOns are bicarbonate (HC03) and calcmm (Ca) whtch average htgher for the Trent Rtver The htgher concentrations m the Trent Rtver are the result of stgmftcant ground-water mflow from the Castle Hayne Ltmestone Htgh color and tron are sometimes a problem wtth water m both estuaries

Some reaches of the Neuse Rtver estuary occasion­ally undergo oxygen depletion due to algal blooms whtch may utthze all avatlable oxygen, resultmg m fish ktlls and the destructiOn of most bottom-dwelhng orgamsms The role of nutnents m promotmg these destructive algal blooms m the Neuse estuary ts dtscussed by Hobbte (1975)

The temperature of the water m the estuanes ts dt­rectly related to the seasons (ftg 3 16) Maximum tem­peratures usually occur m July and the mtmmums m Janu­ary Only small temperature dtfferences are detectable lat­erally m any cross sectiOn and seldom does more than one degree Celsms temperature dtfference extst from the sur­face to the bottom

Hydrology of the Pamhco Sound Estuarme System 57

:z

- u w 0 u 1.0 :z C\1 <( ~ ~ 15,000 u <( :::> 0

10,000 :z (f)

0 0 u :r:

5,000 ~

u 0 a:: 0 u.. u

u ~ w a... -(f) _J 8 w

> ~ w w 7 _J w

u.. 6 a::

w 2 ~ 5 <(

3: 4

:za:: 10

_:::> 0 0

HIGH WATER WINDS ( Northeast w1nds)

-:r: 0

tja:: 10 a_W (f) a.. 20 LOW WATER WINDS (Southwest wmds) ocn I :zw -.....J 23 24 22 3:-~

JANUARY, 1965

Figure 3.15. Effect of wmd on water levels and bottom spec1f1c conductance m the Neuse R1ver estuary at New Bern, January 22-30,1965 Datum of water level gage 1s-6 15ft MSL

Spatial Variations in Salinity

Although water m Pamhco Sound IS usually well mtxed by wmd and currents and IS almost always umform m sahmty from the surface to the bottom, sahmty stratifi­catiOn often occurs near the mouth of the Neuse River es­tuary dunng and followmg penods of sustamed high freshwater mflow Thts stratification IS the result of the hghter freshwater ovemdmg the more dense saltwater StratificatiOn IS even more common further upstream m

58 Hydrology of MaJor Estuar~es and Sounds of North Carohna

the estuarme portions of the Neuse and Trent Rtvers and at times may be qmte pronounced Samples have been collected where the surface-to-bottom sahmty ratio ap­proached 0 01 Usually, however, thts ratio IS not less than 0 8

Lateral sahmty vanatwns withm a cross sectiOn of the wide portion of the estuary are also qutte common The sahmty IS usually higher on the left bank of the es­tuary (m the sense of facmg downstream), a phenomenon attnbuted to the Conohs force, as discussed m the "Gen-

:I -< Q.

0 0 ?J s. =-~ ~ Dol

~ ;::; 0 VI 0 c = Q.

1"1"1

"' c Dol ~

:; ~ VI

~ ;' 3

(o/1

loC

Table 3 4. Summary of chem1cal analyses of water samples collected at key stations m the Neuse-Trent R1ver system Chem1cal constituents are m milligrams per hter, except spec1f1c conductance, pH, and color (Adapted from W1lder and Slack, 1971a )

Hardness 1

~ as CaCO .. -.. 00 ""' ) I <J U ~ -g ON -;;- ~ ""' ~ ., 0~ G ;:;::- 0..... g ~ ':,., .,

~ ... oo ~ 10., ~ ~ § 3 ~ ~ e : : 3 -g § ~ ~:: ~

Station name GJ o c ~ ~ ~ ; ~ 8 .,... .,.. o -;,. ., -o -o ., :> ., a .,.. 10 -.. u co ::1

g t ::~ '8 ~ ::: g. ~ ~ ~ ~ .; ~ 3 ~ -e 0 10 -.; .. ~ '6 ~ ~ .; ~ g ~ ; ., .. ... .D ~ -.< B "- QJ ,. 01 -.< C u c :; ~ ~ ~ -< ~ g !: ::: ::: ";ri ~ Iii, b -e ~ ~ _g ~ ~g 10 C ,.., ~.. ~10 :::: ~ ~ ~ 0 o ..-<~ :1 .C -< ..-< -.<001 COCO 0111 1>.:18 :>:: 0 ~ C ~ ....t ::! tD tn"'"' taJ Vl .....,. U 2: U'l 0-t CCI Vl U t.a.. Z 0 en c::t:: U S Z U V) '"a 0 C.. U

0 20 186 171 16 673 8 4 150 2091814 Neuse River near Ft Barnwell about Oct 1954 daily Max 14 89 65 4 0 25 5 7 204 17 53 3 8 42 11 0 39 5 0 8

3, 900 to Hin 4 0 00 3 0 2 3 8 5 4 3 2 3 4 0 2

2 65 20 4 84 50 ept 196'J Avg 10 19 5 5 1 5 7 4 1 8 20 6 9 8 7 1

7 4 153 117 54 257 8 0 240 2092500 Trent River near Trenton 168 Oct 1951 daily Max 11 77 42 3 2 11 2 J 126 51 12 6 0 40 15 1 31 6 1 14

to Min 1 2 00 4 7 J 1 6 2 10 2 1 2 0 0 1 4 90 54 12 118 94 Aug 1967 Avg 6 3 18 17 1 4 4 J 7 43 9 6 7 0 1

0

eral Hydrology" section In the northern hemisphere, thts force tends to deflect a mass to the nght of Its dtrectton of motion Thus, the salty water mtrudmg up the estuary tends toward the left bank and the fresh water flowmg down the estuary tends toward the nght bank Ftgure 3 17 shows thts effect for the Neuse Rtver as observed dunng a survey of surface spectfic conductance on August 13, 1967 The specific conductance of the water at the left bank was more than 4,000 J.Lmhos while on the nght bank, dtrectly across the channel, It was as low as 1,000 f.Lmhos Thts phenomenon has also been observed m the wtde sectiOns of other North Carolina estuanes

(/)

:::::> (/) 30 .....J w u

Average (/) da1ly w w a:: 20-(..!)

w a

2

-Average/

w a:: :::::> monthly 1-c::r mm1mum a:: w ~

~ w 1- 0

J F M A M J J A s 0 N D J MONTH

Figure 3.16. Range of water temperatures m Neuse R1ver estuary at New Bern from October 1963 through August 1967

Fteld surveys of specific conductiVIty have shown that, for the narrow reaches of the Neuse Rtver and Trent Rtver estuaries, relatiOns between the specific conductance at one locatiOn and the specific conductance at other loca­tions etther upstream or downstream are fauly constant Ftgure 3 18 shows such relatiOns for the Neuse Rtver es­tuary ( vahd upstream from the U S Htghway 17 bndge at New Bern) and the Trent River estuary (vahd throughout Its length) The relation for the Neuse upstream from New Bern IS based on ten specific conductance surveys made by the Geological Survey between September 1954 and September 1968 The relation for the Trent River estuary Is based on mne surveys made dunng the same penod As may be deduced from figure 3 18, the change m specific

60 Hydrology of MaJor Estuar1es and Sounds of North Carohna

conductance for a given distance IS greater for the Neuse Rtver estuary (874 J.Lmhos/mt) than for the Trent Rtver es­tuary (704 f.Lmhos/mt) Thts IS due pnmanly to the greater volume of freshwater flowmg down the Neuse Rtver that reststs the upstream mtrus10n of saltwater from Pamhco Sound On the average, about 4,200 ft3/s of freshwater flows mto the Neuse Rtver estuary at Fort Barnwell com­pared to an average of only about 450 ft3 /s at Pollocksvtlle on the Trent Rtver estuary

Frequency of Saltwater Intrusion

Information on the frequency of saltwater mtrus10n at vartous locations m the Neuse and Trent Rtver estuanes may have applicatiOn m sttmg mtakes for water supplies Although no smgle water-quahty cntenon may be gtven, It was noted earlier that water wtth a chlonde concentra­tion of 250 mg/L ts unsmtable for pubhc supplies and water contammg more than 500 mg/L ts unsUitable for a vanety of mdustnal uses

The U S Geologtcal Survey collected water sam­ples datly from the surface and bottom of the Neuse at the U S Htghway 17 bndge m New Bern (sta 02092162 on pl 1) from 1957 through 1967 The spectftc conductance of these datly samples was checked agamst the record of a momtor that contmuously recorded the specific conduc­tiVIty of water at the bottom of the channel at the U S Htghway 17 bndge for a 2-year, penod In most cases there was less than 5 percent dtfference between the datly maxtmum recorded by the momtor and the conducttvtty of the datly sample Thts mdtcates that once-datly sampling ts suffictent to detect the presence of saltwater mtrus10n at this locatiOn

A frequency analysts of the spectftc conducttvtty data from the 11 years of daily samples at New Bern (ftg 3 19) shows that at least some saltwater (as mdtcated by a spectftc conductance of 800 J.Lmhos) was present along the channel bottom 60 percent of the time and along the surface about 45 percent of the time

The relation of distance to surface specific conduc­tance (fig 3 18) and the surface specific conductivity fre­quency curve (fig 3 19) were used to estimate the fre­quency of occurrence of vanous specific conductiVIties at pomts m the estuary upstream from the U S Highway 17 bndge (fig 3 20) These estimates are the dashed curves above the solid curve labeled "surface specific conduc­tance at New Bern" on figure 3 20 It should be em­phasized that these dashed curves are generated and only the solid curve ts based on measured data

As an example of the use of figure 3 20, suppose an mdustry desires process water which may have a conduc­tance exceedmg 800 J.Lmhos not more than 5 percent of the time, with water dunng times of exceedance bemg

EXPLANATION

-200- Surface spec1f1c conductance 1n m1cromhos

0 2 3 MILES

0 2 3 4 KILOMETERS

F1gure 3.17. L1nes of equal spec1f1c conductance for the Neuse R1ver estuary, August 13,1967

Hydrology of the Pamhco Sound Estuarme System 61

provtded by emergency storage Where ts the most down­stream pomt along the Neuse Rtver whtch could reasona­bly be expected to meet thts cntena? From ftgure 3 20, the mtersecttOn of the 800 tJ.mhos hne and the 5-percent­exceedance hne falls between 6 and 8 mtles upstream from the U S Htghway 17 bndge at New Bern The mter­polated value would be about 7 5 mtles The mdustry m thts example would probably not want to locate tts water tntakes any further downstream than thts

u 0 \()

N

.... <{

(j)

0 :t: ::::!!; 0 a::: ~ :::!:

~ .

lLJ u z oct 1-u ~ 0 z 0 u

~ ~ u LLJ Q.. (/)

20,000

15,000

10,000

Example If the surface conductance of the Trent R1ver 6 m1les upstream from the mouth 1s 4,800 pmhos, then the surface conductance at the mouth IS about 9,200 JJmhos

<::1 .. ~

9200 pmhos v~ - - - - - - - - - - ~'\b.

5 10 15 DOWNSTREAM DISTANCE, IN MILES

20

Figure 3.18. Change 10 surface spec1f1c conductance w1th upstream and downstream d1stance 10 the Neuse and Trent estuanes

0 LLJUJ ::?:o 5 - LLJ 1-I..LJ 20 u u.x Ow 40 Wa::

I ~0 t--:zo

_j_. SALTY

UJW u....J a::<C w:::> a_O

UJ FRESH

800

100 400 40,000

CONDUCTANCE, IN MlCROMHOS

Figure 3.19. Percentage of t1me that speCific conductances equaled or exceeded mdacated values 1n the Neuse R1ver estuary at New Bern, 1957-67

62 Hydrology of Major Estuaries and Sounds of North Carolina

In the Trent Rtver estuary, datly samples were col­lected by the U S Geologtcal Survey from 1959 through 1961 at a stte 6 5 mtles upstream from the confluence of the Trent wtth the Neuse Rtver at New Bern (sta 02092558 on pl I) The samples were mtegrated surface­to-bottom m a shallow part of the nver where surface and bottom spectfic conducttvtttes were nearly the same A frequency analysts of the dat1y conducttvtttes ts shown m figure 3 21 The added dashed curves represent estimates

w u z <t 1-u ::::> oo Zw oc uw

w cu ~ ~ 5 <t ua: c;o ~ Cl 20

w w--l

~~ t-0

w LL. O<.ll

<t LLJ3: (..!)

<t 1-:z w u a: w Q..

60L-~----~--~~-------L-----L------~ I 00 400 1,000 40,000

SPECIFIC CONDUCTANCE, IN MICROMHOS AT 25°C

Figure 3.20. Percentage of t1me that surface speCifiC con­ductances were equaled or exceeded for several locat1ons 10 the Neuse R1ver estuary, 1957-{)7

01 w u z 0 2 <{ 1-u ~ oc zw 00 u lLJ

w 5 cu

LLJX 1-I..LJ <t ua:: -o 0

~Cl LLJ

w--1 ~ <t - :::> 1- 0

w u. Ocn

<t w 3: (..!)

FRESH SALTY

<{ 1-z LLJ u 0:: w Q..

400 1000 4000 10,000 40,000 SPECIFIC CONDUCTANCE, IN MICROMHOS, AT 25°C

Figure 3.21. Percentage of t1me 10tegrated speCific conduc­tances were equaled or exceeded for several locations m the Trent R1ver estuary, 1959-61

of the frequency of occurrence of various specific conduc­tiVIties at other pomts m the estuary These dashed curves show relatiOns which were generated by usmg the specif­Ic-conductivity-distance relatiOnship for the Trent River estuary (fig 3 18)

At a number of other more downstream locatiOns m the Neuse River estuary, saiimty data were collected by the Umversity of North Carolina Institute of Marme Sci­ences and the Carolina Power and Light Company Data from four of the locations havmg the longest penod of sampling have been analyzed to give some IndicatiOn of the frequency of occurrence of vanous saiimties The data were collected at varymg mtervals, from days to months apart, but with good year-round coverage Figures 3 22-3 25 present saiimty frequency curves for these four loca­tiOns, known as Garbacon Shoals Light, WIIkmson Pomt Light, Hampton Shoal Light, and Fort Pomt Light (pi 1)

The maximum known saltwater mtrus10n mto the Neuse estuary occurred on August 21, 1954, about 65 miles upstream from the mouth and 2 25 miles northeast of Fort Barnwell, when specific conductance averaged 673 J.Lmhos (mdicatmg about 160 mg/L of chlonde) Saltwater has been detected upstream from Street's Ferry, 37 miles upstream from the mouth of the Neuse River (sta 02091836 on pi 1) several times smce 1955, but no mtru­sion to Fort Barnwell IS known to have occurred smce 1954 The pomt of maximum known mtrus10n m the Trent River estuary IS about 4 5 miles upstream from Pol-1ocksville, or about 28 mt1es upstream from the mouth of the Trent (60 miles upstream from the mouth of the Neuse) This extreme mtrus10n was caused by wmds from Hurricane Hazel (October 15, 1954) which came dunng a severe drought when the nvers were expenencmg very low flow

Relation of Salinity to Freshwater Inflow

Although the relations m figures 3 19-3 25 give an overall mdicatiOn of the frequency of saltwater mtrus10n at a number of locatiOns m the Neuse-Trent River system, they do not separate the effects of vanable freshwater In­flows on the frequency of mtrus10n Dunng years of high freshwater mflow, when saltwater IS displaced farther downstream than usual, the likelihood of high wmds push­mg saltwater upstream to, say, New Bern IS less than dur­mg years of low freshwater mflow, when tides or wmd­dnven currents need not push the water as far upstream to reach New Bern

To show these effects of freshwater mflow at key locatiOns, specific conductance data for the Neuse River estuary at New Bern (sta 02092162 on pi 1) were related to the annual freshwater discharge of the Neuse River at Kmston (fig 3 26), and mtrus10n data for the Trent River estuary near New Bern (sta 02092558 on pi 1) were re-

lated to annual freshwater discharge of the Trent River at Trenton (fig 3 27) With these relattons, It IS posstble to estimate the number of days when saltwater was present durmg a given year For example, If the annual average discharge at Kmston was 1 08 (ft3/s)/mi2 for a given year, then water at the surface of the Neuse River estuary at New Bern would have been expected to have a specific conductance of 800 J.Lmhos or greater 49 percent of the time ( 179 days) dunng that year, and the specific conduc­tance of water at the channel bottom would be expected to exceed 800 J,Lmhos 68 percent of the time (248 days for that year) Furthermore, such conditiOns have a 45-percent chance of occurrence for any year

Management of the Falls Lake proJect m the upper Neuse River basm, by augmentmg low flows with reser­voir storage, almost certamly will reduce the frequency of occurrence of the most extreme saltwater mtrus10n By re­leasmg flood storage at medmm-high flow rates over a long penod of time, the Falls Lake proJect may also re­duce the number of days per year of occurrence of salty water at New Bern, but no ngorous analyses of this specu­lation have been made

Generally, conditiOns of mmimum saltwater en­croachment m the Neuse and Trent River estuanes occur dunng the month of Apnl and conditions of maximum saltwater encroachment occur m December (ftgs 3 11 and 3 12) This may seem surpnsmg because maximum dts­charges of the Neuse River occur m February, on average, and mimmums occur m June However, changes m salin­Ity due to changmg freshwater discharge occur slowly m these estuaries because of the dampemng effect of Pam­IIco Sound

THE TAR- PAMLICO RIVER SYSTEM1

The Tar-Pamiico River system (pl 1) drams a total area of 4,300 mi2

, with an average annual outflow of about 5,400 ft3 Is The upper part of the nver basm hes m the Piedmont Provmce and the lower part m the Coastal Plam The largest tnbutary to the Tar-Pamhco Rtver sys­tem IS Fishmg Creek (dram age area 860 mt2

) Other Im­portant tnbutanes mclude Cokey Swamp Creek, Conetoe Creek, Tranters Creek, and the Pungo River

Actually, the Tar Rtver and the Pam II co Rtver are one and the same watercourse Upstream from the mouth of Tranters Creek (pi 1), whtch IS about 39 miles up­stream from the mouth of the Pamiico Rtver, tt IS known as the Tar River, downstream m the wtdenmg segment openmg mto Pamiico Sound, tt ts known as the Pamiico River

The U S Army Corps of Engmeers mamtams a navtgattOn channel m the Tar-Pamiico River 200 feet wtde and 12 feet deep from the mouth of the Pamiico Rtver to Washmgton (about 38 mtles upstream from the mouth of

Hydrology of the Pamlico Sound Estuarme System 63

26 I I l l

24

22

20

a z 18 <I CJ)

::::> 0 ::I: 16 ~

a:: I..LJ (i.

14 CJ) ...._ a:: <I

12 (i.

z

- 10 >-~

z _J

<I 8 CJ)

6

4

2

""'~~, ...

'~ "' "-.. " " 6>

' J', ~)' (/ 1> ..... )'I.]~-

~c~ "Z ~ '~

" ""' "' "' '· .....

"' " "' "" ' ' " "' '-'n ' ' " "'-~

' ~

"" ~

I'--~

~ ~~

0 I I I I

0 01 01 05 2 5 10 20 30 40 50 60 70 80 90 95 98 99 5 9 9 9 PERCENTAGE OF TIME INDICATED SALINITY WAS EQUALED OR EXCEEDED

Figure 3.22. Percentage of t1me surface and bottom salm1t1es were equaled or exceeded m the Neuse R1ver estuary at Gar­bacon Shoals L1ght, 1948--68 Data are from the Umvers1ty of North Carolma lnst1tute of Manne Sc1ences, Morehead City, N C , and the Carolina Power and L1ght Company

64 Hydrology of MaJor Estuaries and Sounds of North Carohna

22 ' I "'I

20 ...

18

a z 16 <X (f)

=> 0 ::I:

14 .......

0:: w Q..

12 (f)

.......

-.... ..........

' ~ <90 ·/' -- ,)-0

"' .~

~ J'G--

.. ~~

0:: <X Q.. 10

1\.~C' -"""~ z

>- 8 .......

z _J

<X 6 (f)

4

2

1'\ [' __ .. ' 1\

' ...

l\ \ ~

"'~ \ "' ~ ~ I I I I 0

001 01 05 I 2 5 10 20 30 40 50 60 70 80 90 95 98 99 5 99 9

PERCENTAGE OF TIME INDICATED SALINITY WAS EQUALED OR EXCEEDED

F1gure 3.23. Percentage of trme surface and bottom salmrtres were equaled or exceeded m the Neuse Rrver estuary at Wrl­kmson Pomt Lrght, 1958-67 Data are from the Unrversrty of North Carolma lnstrtute of Manne Scrences, Morehead City, N C , and the Carolina Power and Lrght Company

the Pamhco River), 100 feet wide and 12 feet deep from Washmgton to a tummg basm at the mouth of Hardee Creek, a tnbutary to the Tar River, and 75 feet wide and 5 feet deep from Hardee Creek to Greenville

The combmed surface area of the Pamhco and Pungo Rivers IS rather large, about 225 mi2 However, depths are shallow, averagmg only about 11 feet The total volume of the Pamhco River estuary (mcludmg the open-water segment of the Pungo River) IS about 69 bii­hon ft3

The mfluence of ocean tides extends upstream to Greenville on the Tar River, about 59 miles upstream from the mouth of the Pamhco Rtver estuary Due to the dampemng effect of Pamhco Sound, tide ranges near the mouth of the Pamhco River are less that 0 5 foot How­ever, due to the funneling effect of decreasmg channel dt­menstons m the upstream dtrectiOn, tide ranges at Washmgton approach I 0 foot Tide ranges m the Tar River have not been studied, but decrease to nothmg near Greenville

Hydrology of the Pamhco Sound Estuarme System 65

0 2 <( (f)

:::> 0 I .._ a:: w CL.

~ V'

4

2

0

8

' I I I

~

--~

~

"' ~ <90 - - /'/'_ -

?~

-~ ~

~u~}:' (f)

........ a:: <( CL.

z 6

- ~C'ct

~

i~t >­........

z _J

<( (f)

4

2

0 I

1\ "'-""

~

"-l..'-... I I I

001 0 I 05 TIME

I 2 5 10 20 30 40 50 60 70 80 OR

90 95 EXCEEDED PERCENTAGE OF INDICATED SALINITY WAS EQUALED

Figure 3.24. Percentage of t1me surface and bottom sahmt1es were equaled or exceeded m the Neuse R1ver estuary at Hampton Shoals L1ght, 1958-60 Data are from the Umvers1ty of North Carolma Institute of Manne Sc1ences, Morehead City, N C

As IS the case m the Neuse-Trent system, wmds play a far more Important role than either lunar tides or freshwater mflow m generatmg currents and m changmg water levels m the Pamhco River For example, on Sep­tember 19, 1955, Hurricane lone produced surges of about 7 0 feet above mean low water at Washmgton, as re­corded on a U S Army Corps of Engmeers recordmg tide gage

Although saltwater mtruston m the Pamhco Rtver occurs frequently, m the Tar River saltwater rarely pene­trates more than a few miles upstream from the mouth The greatest known penetratiOn of saltwater mto the Tar Rtver occurred on October 15, 1954, followmg an ex­treme drought penod and dunng a large mflux of saltwater due to Humcane Hazel, on thts day a specific conductance

66 Hydrology of MaJOr Estuaries and Sounds of North Carolina

of 15,600 J.Lmhos (5,800 mg/L chlonde) was measured at Gnmesland (sta 02084171 on pi 1), whtch ts about 4 7 mtles upstream from the mouth of the Tar Rtver The hkehhood of occurrence of an extreme drought followed Immediately by a maJor humcane ts difficult to determme, but the recurrence mterval of two such events occurrmg m successiOn IS probably more than 100 years If we assume that sahmty gradients along the channel of the Tar are stmtlar to observed gradtents m the Pamhco, then the salt­water front (200 mg/L chlonde) mtght have penetrated to about 16 mtles upstream from the Gnmesland statiOn on that date

Destructive algal blooms are a recumng problem m the Pamhco Rtver estuary Blooms of algae, predomin­antly dmoflagellates, occur each late wmter or early

0 2 <t (/')

::> 0 :r:: ~

2 I I T T

8

6

4

'\ ~

1.\ <90

/-/'

...

a:: lJ..J a..

2 ' . (/')

~ a:: <t a..

z

->-..... z _J

<t (/')

SURFACE 0 I

8 ""

6

4

2

0 I I I I

0 01 0 I 0 5 I 2 5

~-\ 1\ ' 1\ --

\ ~

'\ 1\ . ~ ~

i'..l"-• -........I --

10 20 30 40 50 60 70 80 PERCENTAGE OF TIME INDICATED SALINITY WAS EQUALED OR

90 95 EXCEEDED

F1gure 3.25. Percentage of t1me surface and bottom sahmt1es were equaled or exceeded m the Neuse R1ver estuary at Fort Pomt L1ght, 1958--67 Data are from the Umvers1ty of North Carolma Institute of Manne Sc1ences, Morehead City, N C

spnng and each summer (Hobbie, 1974) Hobbte attn­butes the wmter blooms to high concentratiOns of mtrate m runoff from the Coastal Plam after crops are harvested and forest growth slows m the fall and wmter Summer blooms may be caused by a combmatwn of moderately high concentrations of nutnents entenng the estuary, utth-

zat10n by algae of nutnents already present m the sedi­ments m the estuary, and higher rates of biOlogical pro­ductiVIty due to warmer temperatures

Summer dieoffs of all or nearly all bottom-dwelling orgamsms m the Pamhco Rtver are common when sahmty stratificatiOn IS present At such times, the decompositiOn

Hydrology of the Pamhco Sound Estuarme System 67

2 0 I w 2 <.!)

a:: a:: t- 18 5 c:t<t w ::r:::W w u>-LL...

0 (/)

10 c;w ~ u

16 z

- w -p wo CD-.J ..-(\ ::::>_ <.!)>-u~ v

~ <(z 20 ~<t zw 14 -a:: ("l >

_<t 0 <(2

w=> ~ 30 <.!)0 " 0

-.Jo crcn I 2 c:. 0 <tw <t '). 40

=>o ::r::: a:: v 0 Zw u w ----- ~-o zw (/) CL Example ~ 50 <(u

10 LL...x C) 1 n text ow C) 60 w z wa:: <.!) 0 <((_)

8 70 uO a:: w ::z: w (/) <t C) > 80 ::r:::w <t u-.J

a:: <( w 6 so w=> -.Jo_

<( <.!)0 ::::> -95

<(w ::z: t-::z: 4 98

::Z:<.!) W::z: <t u-a::w wen

2 CL

0 20 40 60 80 100 PERCENTAGE OF TIME 800-MICROMHO

CONDUCTANCE WILL BE EQUALED OR EXCEEDED

Figure 3.26. Percentage of t1me a conductance of 800 tJ.mhos will be equaled or exceeded m the Neuse R1ver at New Bern for vanous annual average d1scharges at Kmston (dramage area-2,690 m12

)

of dead orgamsms (mcludmg algae) on the nver bottom may utthze all available oxygen, whtch IS normally re­plemshed by mtxmg wtth the more-oxygen-nch water htgher m the water column However, stratification pre­vents or greatly mhtbtts this mtxmg, thus contnbutmg to the death of fish as well as clams, other bivalves, snatls, and manne worms

Several mvesttgators, mcludmg Hobbte (1974), have estabhshed that phosphorus IS almost certamly not a hmttmg nutnent m producmg algal blooms m the Pamhco River-phosphorus always bemg present m sufficient amounts to produce blooms Carpenter ( 1971) showed that phosphate m the effluent discharged to the Pamhco Rtver estuary from phosphate mmmg operatiOns near Beaufort (pi 1) was superfluous to reqmrements for algae produc­tiOn m the estuary

Davis and others ( 1978) found that substantial amounts of orgamc carbon and nutnents are trapped wtth­m the Pamhco Rtver sediments and that these may be Im­portant contnbutors to algal blooms, particularly dunng the summer

68 Hydrology of MaJOr Estuaries and Sounds of North Carohna

2 0 2 w

5 <.!)a:: t- a::<t w

I 8 10 <tw w G>-LL... (/)

u - w 20

oz CD w 16 wo ::::> _J

u <.!)>-~ <tz z w 30 ~<t

a:: 14 > _<t <t z w=> <.!)0 40 _J a:: en

I 2 <to <t ::::>w ::r::: cr zo u w 50 zw (/) CL <tw u C) 10 X

60 LL...w C) 0 w z <.!) 0 a:: <t u 70 ~0 a:: w 8 w (/) ::z: > <(C) <( 80 :::cw

a:: u _J

w 6 <(

_J CL 90 w=> <t <.!)0 ::::> <tw ::z: 95 z t-

<t 4 ::Z:<.!) W::z: u-a::W wen

2 CL

0 20 40 60 80 100 PERCENTAGE OF TIME 800-MICROMHO

CONDUCTANCE WILL BE EQUALED OR EXCEEDED

Figure 3.27. Percentage of t1me a spec1f1c conductance of 800 tJ.mhos w1ll be equaled or exceeded m the Trent R1ver near New Bern for vanous annual average d1scharges at Trenton (dramage area-138 m12

)

Water Levels

As previously mentioned, wmds are the most Impor­tant force affectmg water levels m the Pamhco Rtver Wmds from the east-southeast, blowmg parallel to the channel axis, have the maximum effect m producmg htgh water levels m the Pamhco River, whtle wmds from the opposite directiOn, west-northwest, have the maximum ef­fect m producmg low water levels The wmd dtagram (fig 3 28) for resolvmg a gtven wmd to the directiOnal component effective m causmg water level changes m the estuary IS similar to the one prepared for the Neuse Rtver estuary (fig 3 13), values are based on the cosme of the angle between the actual duectiOn of the wmd and the di­rectiOn causmg the maximum effect In the case of the Pamhco River, the axis of maximum effect forms an angle of about 1 00° from north

Figure 3 29 provides an example of the sensitivity of water levels m the Pamhco Rtver to wmds Actual wmd speeds for the penod February 22-March 2, 1966,

w--

94 98 1

98

94 87

77 87

N

r 64 50 34 17 0

0 17 34 50

I s

77 87

, 98

94 87

6477

94 --E

98

Fagure 3.28. Wmd d1agram for the Pamhco R1ver estuary See text for explanation

~ 6 w

UJ u..

z 5

~ :::c C)

w 4 :::c

w C)

c::r 3 C)

0 30 z 3:

0:: 20 U..::::> Oo

~ :::c

ZO:: 10 WUJ

~CL CL ~(/) 0 ow u::;! ~

w 10 ~z ~-u w

20 u.. u.. w

FEBRUARY

as recorded at the National Weather Service statton at Cape Hatteras, were resolved to their effective compo­nents along the channel axis of the Pamhco Rtver and plotted below a hydrograph of water levels recorded by the Corps of Engmeers for the same penod for the Pam­hco Rtver at Washmgton The close correlatiOn Is appar­ent The response of water levels to wmd IS strong and Immediate and, except for a lull m the wmds on Feburary 26, the mfluence of lunar ttdes on water levels IS com­pletely overshadowed by wmd effects

Ftgure 3 30 relates the effective component of Cape Hatteras wmd velocity to the change m water level of the Corps' gage at Washmgton The relatiOn IS of the same type presented earher for the Neuse Rtver at New Bern (ftg 3 14), for whtch an example of Its use was gtven m the text The relation may be used to predict the approxi­mate nse m water level at Washmgton m response to east­southeast wmds of various magmtudes Thts mformat10n may prove of value m hurrtcane wammgs and m asstgnmg flood nsks to streambank areas

MARCH

Fagure 3 29. Water levels m the Pamhco R1ver at Washmgton and effect1ve component of wmd speed at Cape Hatteras, February 22-March 2, 1966 Wmd speeds are from Nat1onal Weather ServiCe records, water levels prov1ded by the Corps of Engmeers

Hydrology of the Pamhco Sound Estuarme System 69

50 HURRICANE lONE / 9-19-55

/ /

a:: HURRICANE DONNA / :::::>

0 40 9-11-60 0 / :c

a:: / LU / CL

U') / LU _J

:!E 30

z

c LU LU CL U') 20 c 2

3:

LU > t--u

10 LU LL. LL. LU

o~---~------~------~------~---~------~------~-----~----4-----~ 0 2 3 4 5 6 7 8 9 10

WATER LEVEL CHANGE, IN FEET

F1gure 3.30. Relataon of rase an water level an the Pamhco Raver at Washangton to effect ave wand velocaty

Flow

No flow measurements have been made etther m the Pamhco Rtver or m the tide-affected part of the Tar Rtver Therefore, some of what ts satd regardmg flow m the Tar­Pamhco estuary ts at least partly speculative In the wtde Pamhco Rtver estuary, wmds are undoubtedly the maJor short-term mfluence on flow, followed m tmportance by

70 Hydrology of Ma)or Estuar1es and Sounds of North Carohna

ocean ttdes and lastly, freshwater mflow Freshwater m­flow ts probably more tmportant m mfluencmg short-term flows m the narrower Tar Rtver than etther wmds or ttdes However, freshwater mflow and the resultmg net outflow are deftmtely the most tmportant long-term mfluence on flow m both nvers

The channel of the Pamhco Rtver, unhke that of the lower Tar Rtver, ts vastly overstzed for the amount of m-

commg freshwater tt must carry Therefore, veloctttes due to freshwater mflow are very low For example, at the mouth of the Pamhco Rtver, the average veloctty due to the average annual freshwater outflow of 5,400 ft 3/s ts less than 0 02 ft/s On a monthly basts, esttmated average freshwater outflow~ from the Pamhco Rtver, m cubtc feet per second, are as follows

January 7,700 July 3,500 February 10,000 August 5,100 March 8,000 September . 3,200 Apnl 5,200 October 3,700 May 6,800 November 4,300 June 2,400 December 4,900

Annual average flows vary constderably from year to year (ftg 3 31) For example, there IS a 99-percent chance that the annual average flow at the Tar Rtver at Tarboro (sta 02083500 on pi 1) m any one year wtll be equal to or less than 1 8 (ft3/s)/mt2

, but only a !-percent chance that tt \

wtll be equal to or less than 0 39 (ft3/s)/mt2

Ltkewtse, wtthm-year variatiOns m low flows may be considerable (fig 3 32) Thts type of low-flow mformat10n may be apphed to studtes of cntteal water supply, sewage dtlutiOn, and flow-related btologtcal processes (mcludmg algal blooms)

Htgh-flow frequency curves (ftg 3 33) give an mdtcatwn of the amount of flushmg that may take place m the spnng months Adequate flushmg ts a key factor m preventmg destructive algal blooms, and htgh-flow frequency curves, used wtth htstoncal data on algal blooms, may help to predtct the frequency of occurrence of such blooms

r-w

w _J

Water Quality

The chemtcal quahty of the freshwater entenng the Tar-Pamhco Rtver system ts usually, where not contami­nated, of acceptable quahty for pubhc supplies and most mdustnal uses, wtth a mmimum of treatment (table 3 5) Iron sometimes exceeds the 0 3 mg/L upper hmit recom­mended by the U S Environmental Protection Agency (1976) [ 1977] for dnnkmg water and color sometimes ex­ceeds the recommended upper hmtt of 75 color umts given m the same report, but these problems may be re­medied with proper treatment The Cities of Tarboro and Greenvtlle both withdraw water from the Tar River for mumcipal use, whtle the ctty of Washmgton utthzes water from Tranters Creek

Ftgure 3 34 shows average monthly temperatures for the Pamhco Rtver at Washmgton (sta 02084472 on pi 1) The values are based on averages of daily surface and bottom temperature readmgs for the penod October 1961-September 1967 Typically, maximum temperatures occur m July or August and mmtmums m January or Feb­ruary

Sediment

Little IS known about the movement and depositiOn of sediment m the lower Tar River and Pamhco Rtver, but the Geological Survey measures sedtment discharge (ex­cludmg bed-load dtscharge) at the Tarboro statiOn (mean datly sedtment dtscharges are avatlable from 1959-67, In­

stantaneous dtscharges are avatlable from 1974-present), a sedtment-transport curve for thts Statton ts shown m ftgure 3 35 Sedtment dtscharge there through 1976 averaged

w ::E LL..

2 Drainage area is 2140 mi 2 at site -w u a::

OJ c:::r ::::> ::::> u C1

(f)

I I I I I I I I I .~ I I z

a:: w

I_..._........_, I

:Example ...... ,-,-,-, ............ : / -w a.. (!)

~ I I I I 1-- There IS a 50-percent chance 1n any one -

cr 0 c:::r

:r: z u 0

u (f) w 0 3 0 en

1-- year that the annual mean discharge will be - equal to less than I 04 ( ft 3/s) I mi 2 I ' '---or

I I I I I I I I I I I I

95 90 80 70 60 50 40 30 20 5 99 98 10 2 a:: w

PROBABILITY, IN PERCENT a..

Figure 3.31. Frequency curve of annual mean dtscharge of Tar Rtver at Tarboro (AfterW1Ider and others, 1978 )

Hydrology of the Pamlko Sound Estuarine System 71

w .....J 20 2 I I l I I I l I I I I w 0:: ex 10

Drainage area at Tarboro is 2140 mi 2

-:::::::> 0 CJ)

0:: w Cl..

0 :z 0 u w CJ)

0:: w Cl..

01 ~ L4J UJ u..

u -m :::::::> u ~Example

z -+There 1s a 50-percent chance 1n any one

w <.!)

year that the m1n1mum 7- day mean d1scharge ~-+--will be equal to or less than 0 II (tt 3/s) I m1 2

~ 30

~ 0 01 1_____!,1~1 -+-1 ___..LI-----l.I---'-1--L--1 ---'--1 ---L-1 ----1----1 -----1....1--L---~7~ I ~ 99 98 95 90 80 70 60 50 40 30 20 10 5 2 0 5 0

PROBABILITY, IN PERCENT

F1gure 3.32. Low-flow frequency curves of annual lowest mean d1scharge for md1cated number of consecut1ve days for Tar R1ver at Tarboro (After Wilder and others, 1978 )

about 59 (tons/mi2)/yr for the 2,140 mi2 dramage area This value mcludes sediment contnbut10ns from about 500 mi2 of the hilly Piedmont Provmce, thus, It IS not typical of contnbutwns from the lower 2,160 mi2 of the basm which hes m the flat Coastal Plam Provmce Data from Creepmg Swamp and Palmetto Swamp watersheds (Wm­ner and Simmons, 1977) mdicates that sediment dis­charges from streams drammg Coastal Plam areas of the lower Tar-Pamhco basm are sigmficantly less than for streams drammg the Piedmont Provmce Values over the 3-year penod 1974-76 for three stations m the Creepmg

72 Hydrology of MaJor Estuaries and Sounds of North Carohna

Swamp and Palmetto Swamp watersheds averaged about 38 (tons/mi2)/yr and these values were considered high be­cause of above average water discharge for those years However, If we accept these values as typical of the 2, 160 mi2 area below the Tarboro station, then the average an­nual sediment yield of the entire Tar-Pamhco basm might be about 208,000 tons The ultimate fate of all this sedi­ment IS uncertam, but at least some IS deposited m the Tar and Pamhco River estuaries and some m Pamhco Sound It Is not known how much, If any, eventually reaches the Atlantic Ocean through the mlets to Pamhco Sound

J: -< Q.

a 0 ~ a. -=r ~ ""C AI

i ;:; 0 VI 0 c ::I Q.

rT'I ~ c AI ... s ~ VI -< Cl> ;-3

....... ~

0

0

Table 3.5. Summary of chem1cal analyses of water samples collected at key stat1ons m the Tar-Pamllco R1ver basm Chem1cal concentrations shown are m milli­grams per liter, except spec1f1c conductance, pH, and color (From Wilder and Slack, 1971a )

Dissolved Hardness 1. "' 01 i 4 solids as Caco

3 u 0

Gl "' -; ~ 4 ..... s .., 0 ~i ... ., 0 ~ -; ~ Gl e !:, "" c 0

Station name 01

.... co >. c .... u .... 0 '-" .... ., 0 ...

Gl u 01 "' Qj ~ g z ~ 01 z ~ :: u.!:l .....

c ... 0 c coc

~ ~ '-"

2~ Gl Gl '-" Gl 01 Gl

CON ..... c Gl lao ~ ..... ..... :: ~ ~ .... .... ...... 01 .!:l~~ 0 II

~ i1 "8'ci. ..... :I 01 ~ Ill a "' II 01 II 01 a "' g ~g

.-<a- Gl ... 0 ..... Gl :I Ill ... o 01 ... .... .s: :::IU ..... :I II ::: ~~~ .,... a C.GI .. Gl ..... c:: 0 c:: ..... 01 OIU .... 0 0 01 a. .,. :I ~;, Jl .. 01 c:: ... 01 a ... .... :> ..... 0 ..... co ., .... u:c ..... ..... :I .. "' .... 0 u I ...

~~~ 0

.... Cl ... ... Gl"' 01 ..... ~ 01 ... .. 01 ::! 0 0 ..... ~ :I .s: ..... .... 0 CIICIO ..... ..: a c:: 01 ..... "' 0 "" "' "' ..... u "' "" oQ "' u lao ..... .s: II.-< 01 0 u :c 0

z "" ~ u u z "' a. u

2083500 Tar River at Tarboro, N C about Oct 1944 daily Max 19 67 9 0 2 6 22 2 9 69 13 54 3 6 8 1 0 111 102 33 14 270 7 7 140 2,140 to Min 6 2 00 2 8 5 3 0 6 7 1 1 2 4 0 1 00 45 33 9 0 47 5 6 3

June 1968 Avg 13 16 5 4 1 6 7 6 1 8 24 5 9 7 6 1 1 2 31 64 50 20 2 83 35

2084000 Tar River at Greenville, N C about Oct 1948 monthly Hax 19 72 9 2 2 6 12 2 6 32 15 15 3 3 0 30 79 79 32 11 121 7 4 120 2,620 to Hin 3 7 00 3 2 8 2 9 7 6 2 5 1 8 0 1 00 44 30 13 0 39 5 4 7

Aug 1967 Avg 12 22 5 2 1 6 6 2 1 8 21 6 7 6 6 0 1 7 1 3 66 42 20 2 79 45

2084124 Tar River near Pactolus, N C about !oct 1956 daily Hax 18 56 9 0 3 2 12 2 8 76 19 20 3 13 85 60 26 147 8 1 120 2,680 to Min 6 9 00 3 4 8 2 3 1 0 8 2 7 4 4 0 6 48 13 0 51 5 9 10

Sept 196( Avg 12 14 5 5 1 8 6 4 1 8 19 6 8 7 6 1 2 3 65 21 5 81 45

0 30,000 z 0 u w

Dramage area 1s 2140 m12

(/)

a:: w Q..

I- 20,000 w w LL

u al :::::> u

z 10,000

w <.!)

a:: <l I u (/)

0 0 I 01 I I 15 2 3 4 5 10 20 30 40 50 100

RECURRENCE INTERVAL, IN YEARS

Figure 3.33. Max1mum 7- and 30-consecutlve-day average d1scharges of the Tar R1ver at Tarboro

30 (f)

::::::> (f) _J

25 w u

(f)

w 20 w

0:::: (.!)

UJ Cl

15 :z

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC

f•gure3.34. Average monthly temperature of Pamllco R1ver atWashmgton, October1961-September1967

74 Hydrology of MaJor Estuaries and Sounds of North Carolina

LU (..!)

a::: c::tO ::r:Z uo (.I)U - LU 0(./)

a::: a:: Ww ~a.. 3:

........ LU

(.I)LU ::::>lL. 0 LU U ;z­<{CD ........ ::::> zu <{ 1-;z (./)-

z

INSTANTANEOUS SUSPENDED SEDIMENT DISCHARGE, IN TONS PER DAY

F1gure 3.35. Sediment-transport curve for the Tar R1ver at Tarboro, based on measurements made dunng 1974-76

Salinity

Daily dunng the penod October 1961-September 1967, the U S Geological Survey determmed surface and bottom sahmty values m the Pamhco R1ver at Washmgton (sta 02084472 on pi 1) m terms of specific conductance and chlonde concentratiOns These pomt data were supple­mented by 10 specific-conductance surveys made by boat dunng the penod September 14, 1954-September 27, 1968

At low sahmties, the Pamhco River water IS usually well mixed vertically, but Geological Survey data suggests that stratificatiOn IS common when specific conductance IS

greater than 800 tJ.mhos (fig 3 36) and bottom sahmties may exceed surface sahmttes by 50 percent or more Geological Survey data, as well as data compiled by Wil­liams and others (1967), show that sahmttes are very often higher near the left bank (m the sense of facmg down­stream) than on the nght This phenomenon (due to the Conohs component of acceleration of the Earth's rota­tiOn), was dtscussed m the "General Hydrology" sectton and appears more pronounced m the Pamhco Rtver es­tuary than m any other North Carohna estuary

Conductivity surveys have shown that, wherever salty water ts present wtthm the Tar-Pamhco estuary, there ts a relatively constant relatiOn (ftg 3 37) between etther surface or bottom spectfic conductance at one loca-

u 0

ll'\ N

E-< -~ w

uo:: ~~ t;~ :::>H

~ ~ 1000 OW uu uo:: HW ~Cl. H UCfl WO (;)~

0 0:: u H :;;:::

z H

100

I Z 5 I 0 20 50 80 90 95 98 99

I"-

" 1 1 r r 1 1 1 1 1 1 I

l-1-- Curve based on 1800 do1ly

'" bottom observottons for the -

~ ~ per1od Oct 1961 to Sept 1967 = 1'-

" " -\ Curve based on 1812 dolly =

~ f-1 surface observottons for the_ 1\ \ per1od Oct 1961 to Sept 1967

\ \

txomple Spectf1c conductance t-

1 exceeds 800 about 23 ..__

' percent of the t1me -f- !-'""

\

\ ~

""" ~ ["""'-o..

I Z 5 10 20 50 80 90 95 98 99

7200

3250

2530

1850 1500 0::

w 1200 £,-<

H

880 ...J

0:: w

310 Cl.

Cfl

~ 250 L'

H

200 ...J ...J H

145 z 120 z

H 90

65 w 0 H 0::

40 0 ...J ::r: u

PERCENTAGE OF TIME SPECIFIC CONDUCTANCE OR CHLORIDE

CONCENTRATION IS EQUAL TO OR GREATER THAN A GIVEN VALUE

Figure 3.36. Cumulative frequency curves of spec1f1c con­ductance and chlonde, Pamllco R1ver at Washmgton (After Wilder and others, 1978)

Hydrology of the Pamhco Sound Estuarme System 75

u 20,000 0 I.(')

N Example If the surface specrfrc conductance at a g r ve n ~ locotron rs 9,150 J.Jmhos, then the surface specrfrc <X conductance 5 m rl es downstream should be about

12,150 ,umhos A s rm rio r example c ou I d be g r ve n (/)

0 15,000 for bottom speclfrc conductance I ~ 0 0:: 12,150 J.Jmhos u ------------------------~

z 10,000 9,150 JJ m~os

--------- -----w u z <X ~ u => a z 5 000 0 u

u u....

u w a...

0 (/)

0 5 10 15 20 25 30

DOWNSTREAM DISTANCE, IN MILES

F1gure 3.37. Relatron between surface specrfrc conductance at one pornt rn the Pamlrco Rrver estuary and surface specrfrc conductance at other pornts erther upstream or downstream

t10n and the correspondmg surface or bottom specific con­ductance at other locatiOns either upstream or downstream, this relatiOn IS apphcable from the mouth of the Pamhco River upstream to a pomt m the Tar River about 6 5 miles upstream from Its mouth at Tranters Creek-a total dis­tance of 46 5 miles In thts reach, spectftc conductance gradients average about 610 J.Lmhos/mi

Sigmficant saltwater mtrus10n (200 mg/L chlonde or more) IS present at W ashmgton only about 23 percent of the time (fig 3 36), but the frequency of sigmficant salt­water mtrus10n qmckly mcreases m a downstream duec­tiOn At the mouth of the Pamhco River, chlonde concen­tratiOns are seldom less than 2,000 mg/L, even dunng penods of high freshwater runoff

The frequency of saltwater mtrusion m the Pamhco River estuary IS, of course, mversely related to freshwater mflow Annual average discharges of the Tar River at Tarboro (sta 02083500 on pi 1) were plotted agamst per­centage of tlme that a specific conductance of 800 J.Lmhos or greater was recorded at Washmgton for each year dur-

76 Hydrology of MaJor Estuaries and Sounds of North Carohna

mg the penod 1962-67 (fig 3 38) The mterpretat10n of figure 3 38 IS simllar to that of figure 3 26 for the Neuse River estuary The percentage chance of occurrence (or recurrence mterval) of a given annual average discharge and associated specific conductance condltlons may be es­timated from the nght-hand ordmates

Of greater mterest, perhaps, IS the movement of the saltwater front (200 mg/L chlonde) m response to chang­mg freshwater mflow from the Tar River (fig 3 39) The shape of the curve Indicates that when the saltwater front IS at or downstream from Washmgton, a large change m freshwater mflow IS reqmred to produce sigmficant move­ment of the front, whereas when the front IS located 2 or more mlles upstream from Washmgton, even a relatively small change m freshwater mflow may produce sigmflcant movement of the front This general response pattern IS typical of most estuanes The relation of figure 3 39, though not well defmed for higher flow rates and fauly m­accurate at low flow rates, Is useful m estimatmg the ad­vance or retreat of the saltwater front under most flow

20 LL.J

~ w w u..

1.3 Interpretation of th1s graph IS

s1m1lar to that of f1gure 3 26

(.!)

a: a: <t<t IW

o Surface 30 ~>-1.2 • Bottom Ow

u LL.J

CD....J - 1.1 u~

zw a:: 1.0 <l

w=> (.!) 0 9 o::U)· <(

I a: u LL.J U) a... 0

0 z

wo <.!>U

.8

.7

<( LL.J 6 0:: U) •

w >a: <( LL.J 5

a...· ....J <( ::::> z z <(

.4

.3

0

•

40

50

60

70

80

90

95

98

z wo (.!)

<(>-a:Z w<(

> <lZ

....J 0 <(W ::::>0 zw zW <(u

X u_W

00:::

wO u z 0 <tW :I:....J u<t

:::> wO <.!>w <t .,..._ (.!)

zz ww UCD a:: w

.2~--~--~--~--~--~--~--~--~~--~~ CL

0 20 40 60 80 100 PERCENTAGE OF TIME 800 MICROMHOS WILL

A SPECIFIC CONDUCTANCE OF BE EQUALED OR EXCEEDED

Figure 3.38 Percentage of t1me a spec1f1c conductance of 800 J.Lmhos will be equaled or exceeded m the Pamllco R1ver at Washmgton for vanous annual average d1scharges at Tarboro (dramage area-2,140 m1 2

)

conditions The relatiOn of figure 3 39 may thus be useful m planmng for Withdrawals of freshwater for mumcipal or mdustnal supply and for evaluatmg the Impact of mduced sahmty changes on estuanne orgamsms Regardmg the latter, the National Techmcal Advisory Committee to the

Secretary of the Intenor (1968) recommended that, based on studies of the effects of sahmty changes on estuanne species, no changes m hydrography or stream flow should be allowed that would permanently change sahmties m an estuary by more than 1 0 percent from natural vanat10n

Hydrology of the Pamhco Sound Estuarine System 77

10

9

8

7

(/') 6 w _J

~

5 z

w 4 u z <! I-(/') 3 -a

2 E 0 Q)

'--V> a.

:::>

0

E 0 Q)

'--V> c:: ~ 2 0 a

-

0

(f)

c: ::u , 1:::» ("")

rn

11-4-54 9-30-54

11-30-54 ~4-15-54

u-+-- 9-27-68

0

10-8-53

200 400 600 800 1000

US 17 BRIDGE AT WASHINGTON

1400

7-28-66 0

1800

DISCHARGE, IN CUBIC FEET PER SECOND

2200

Figure 3.39. Relat1on between the precedmg 30-day average d1scharge of the Tar R1ver at Tarboro and the locat1on of the saltwater front. A 7-day lag t1me IS applied to the 30-day flows

78 Hydrology of MaJOr Estuaries and Sounds of North Carolina

4. Hydrology of the Albemarle Sound Estuarine System

For purposes of thts report, the Albemarle Sound system (pi I) mcludes not only Albemarle, Currituck, Roanoke, and Croatan Sounds, but also the estuanes and associated dramage of the Roanoke, Chowan, Per­qmmans, Little, Pasquotank, North, Alligator, and Scup­pemong Rtvers and all other land areas tnbutary to Al­bemarle Sound The system drams a total area of 18,359 mt2

Broadly speakmg, the Albemarle Sound estuanne system has much m common wtth the Pamhco Sound es­tuarme system, that IS, ttde ranges are of small magmtude m most locations, and wmds play a maJor role m water circulatiOn m the sounds and m the wtde lower parts of the estuaries The Albemarle Sound system has no dtrect outlet to the ocean, but connects to Pamhco Sound and Oregon Inlet through Croatan and Roanoke Sounds Hence, dampenmg of ttdes IS greater m the Albemarle system than m the Pamhco system Sahmttes are generally lower m the Albemarle system than m the Pamhco system for several reasons First, the total average outflow from Albemarle Sound ( 17,300 ft3/s) IS larger relattve to tts vol­ume (5,310,000 acre-ft) than Pamhco Sound (32,000 ft3/s and 21,000,000 acre-ft) The htgher current strength re­sultmg from thts ts sufficient to more effectively block sahne water from the system Furthermore, seawater that does reach Albemarle Sound has already been diluted m Pamhco Sound

The data on which the followmg discussions are based are from vanous sources Plate I shows the loca­tiOns of key Geological Survey discharge and water-qual­tty data-collectiOn stations used to help define freshwater mflow, freshwater quahty, and sahmty charactensttcs wtthm the Albemarle Sound system Other data sources are acknowledged where appropnate

ALBEMARLE SOUND AND VICINITY

Albemarle Sound (pi 1) IS a drowned nver valley estuary whtch hes behmd the North Carohna Outer Banks The closest oceanic connection IS to the south at Oregon Inlet The sound covers an area of about 480 mt2

, has an east-west dimensiOn of about 55 miles, and averages about 7 miles wtde Etght overs, mcludmg the Roanoke and the Chowan, and Currituck Sound, dram mto Al­bemarle Sound (total dramage area of 18,359 mt2

), whtch m tum drams through Croatan and Roanoke Sounds mto the northern part of Pamhco Sound

The maximum depth of the sound IS almost 30 feet, but most of the central area of the bay IS httle more than 18 feet deep (fig 4 I) The bottom sedtments, whtch con­SISt mamly of fine-to-medmm sand around the margms of the sound (fig 4 2), grade soundward to silt and clay m the deepest areas (Folger, 1972)

Albemarle Sound IS an Important hnk m the Atlantic Intracoastal Waterway Albemarle Sound and Its tnbutanes have proven to be exceptiOnally favorable habitats for anadromous ftshes such as stnped bass and hemng and serve also as nursenes and commercial and sport ftshenes for a vanety of shellfish and fmfish

Some areas of Albemarle Sound have been closed to shellftshmg owmg to htgh coliform bactena counts Also, very destructive algal blooms resultmg m extensive ftsh ktlls have occasionally occurred m the Chowan Rtver and, more recently m Albemarle Sound Nutnents necessary for algal blooms (pnmanly compounds of mtrogen and phosphorous) are m relative abundance m the Chowan Rtver and Albemarle Sound (Bowden and Hobbte, 1977)

Dtssolved oxygen IS abundant m Albemarle Sound year-round (Bowden and Hobbte, 1977) The percent oxy­gen saturation IS almost always above 60 percent and IS very often above 80 and 90 percent, wtth httle dtfference between top and bottom concentratiOns at any locatiOn

Water temperatures m Albemarle Sound closely fol­low air temperatures, as they do m Pamhco Sound Mint­mum sound suface temperatures usually occur m January, averagmg between 3 and 4 o C for that month, and maximums usually occur m July, averagmg 28° C (Wil­liams and others, 1967) VariatiOns across the open sound at any time are shght, seldom greater than I or 2° C, al­though tnbutary waters are almost always several degrees warmer Vertical temperature vanattons are likewise small, or nonexistent, and surface-to-bottom decreases sel­dom exceed 2 to 3° C (Bowden and Hobbie, 1977)

Heath ( 1975) dtscussed potential water problems as­sociated wtth recent large agncultural developments, m­cludmg livestock operations, m the Albemarle-Pamhco pemnsula Artificial dramage canals designed to quickly remove runoff to the coast may lower sahmttes m coastal salt-marsh environments m southeastern Albemarle Sound to below levels necessary for developmg shnmp, crabs, shellfish, and fmfish The runoff from these agncultural developments may also adversely affect the water quality of Albemarle Sound by contnbutmg substantial amounts of bactena, nutnents, pesticides, and sediment

In Cumtuck Sound, extensive dense floatmg mats of Eurasian watermtlfml, an exotic species of freshwater aquatic plant, have hampered recreational use of large parts of the 153 m12 body of water Among the possible solutiOns to this problem are apphcat10n of herbtctdes, mechamcal harvestmg, and mcreasmg the sahmty of the sound to a level that would ktll the watermtlfml Thts last possible solution would require ratsmg the saiimty of the

Hydrology of the Albt:marle Sound Estuanne System 79

30 40 50 MILES

0 10 20 30 40 50 KILOMETERS

f•gure4.1. Depth, m feet, of Albemarle Sound (From Pels, 1967)

sound to about half sea-strength (Batley and Haven, 1963), a measure that would not only destroy the water­mtlfml, but also the extstmg freshwater ecological system, replacmg 1t wtth a much more sahne one

Water Levels

Wmds and tides are the most tmportant short-term factors mfluencmg ctrculatwn and water levels m Al­bemarle Sound, wtth freshwater mflow from tnbutanes playmg a secondary role The effect of wmds from a gtven duectton on water levels 1s dtfficult to analyze and vanes wtth location m the sound and wtth antecedent wmd and water level conditiOns In general, however, wmd-dn­ven currents from easterly wmds wtll tend to produce lower water levels m the eastern end of the sound and htgher water levels m the western end of the sound and m the Chowan and Roanoke estuartes Wmd-dnven cur­rents from westerly wmds wtll usually have the oppostte effect Northerly wmds tend to cause lower water levels along the northern shores of the sound and m the estuanes there and htgher water levels along the southern shore of

80 Hydrology of MaJor Estuar.es and Sounds of North Carohna

the sound and m the estuartes there Southerly wmds tend, of course, to have the opposite effect Table 4 1, de­veloped from water-level records of the U S Army Corps of Engmeers and wmd data from a NatiOnal Weather Ser­VIce statiOn at Ehzabeth Ctty, shows the general effects of wmds on water levels at eleven locatiOns m Albemarle Sound and vtcmtty

Concurrent records of wmd and water levels at sev­eral locat10ns m Albemarle Sound (ftg 4 3) tend to con­firm the vahdtty of table 4 1, but they also show the role of antecedent condtttons m determmmg water level re­sponse to wmds For example, southeast wmds on July 29, 1960, caused nsmg water levels near Edenhouse and Ehzabeth Ctty, thts ts m agreement wtth general effects predicted from table 4 1 Ltkewtse, falhng water levels on November 30, 1960, due to north-northwest wmds agree m general wtth table 4 I On the other hand, falhng water levels at Ehzabeth Ctty dunng July 30, 1960, are counter to the general effects giVen m table 4 1 Water levels, htgh on July 29 because of easterly wmds, began falhng even wtth the change to westerly wmds early on July 30 Ap­parently, the return flow from the water ptleup on July 29 overwhelmed the expected tendency toward nsmg water

0 10 20 30 40 50 MILES

0 10 20 30 40 50 KILOMETERS

EXPLANATION

- Medium sand 1::.: I F 1 n e sand [: :.=·: .. ·1 Very f1ne sand f-_-:.j Cloy

Figure4.2. Texture of bottom sediments in Albemarle Sound. (Modified from Pels, 1967, after Folger, 1972 .)

levels at Elizabeth City due to westerly winds early on July 30.

Hurricane-force winds may cause much greater changes in water levels than the 1- to 2-foot changes seen in figure 4. 3. Hurricane Donna caused rises of more than 4 feet above mean sea level at Edenton and Elizabeth City during September 11 , 1960, and even greater rises, caus­ing extensive flooding, occurred during Hurricane lone on September 19, 1955. Superimposed on the 1- to 2-foot water-level fluctuations attributable to winds are semidiur­nal fluctuations in the range of about 0.5 foot. These are attributable to ocean tides. Although no measurements of tidal exchange for Albemarle Sound were made during this study, it is apparent from figure 4 .3 that they are much less important than winds in determining water levels at the locations indicated and, by inference, else­where in the sound.

The relative unimportance of freshwater inflow compared to tidal exchange in determining water levels in Albemarle Sound and vicinity may be judged by a state-

ment by Bowden and Hobbie ( 1977) to the effect that the input of water to the sound from a flood tide ranges from 1 1 to 18 times as much as the input from freshwater in­flow. However, when considering net movement of water into and out of the sound over long periods of time, the effects of winds and tides tend to cancel, leaving freshwa­ter inflow the most important factor in long-term net flow.

Freshwater Inflow

Table 4.2 is a gross water budget for Albemarle Sound, showing average monthly and annual values for precipitation on and evaporation from Albemarle Sound and its associated open-water areas, inflow from the Cho­wan River and Neuse River estuaries and from other land areas tributary to Albemarle Sound , and outflow to Pam-1 ico Sound through Croatan and Roanoke Sounds .

Precipitation values for these areas are based on long-term averages from National Weather Service sta­tions at Elizabeth City , Manteo , and Plymouth. Evapora-

Hydrology of the Albemarle Sound Estuarine System 81

Table 4 1. Relat1ve effects ofwmd on vert1cal movement of water levels at selected Jocat1ons m and near Albemarle Sound

Locat1on

Chowan R1ver near Edenhouse Perqu1mans R1ver at Hertford L1ttle R1ver near N1xonton Pasquotank R1ver at El1zabeth C1ty North R1ver near ColnJock Curr1tuck Sound at Po1nt Harbor Albemarle Sound near K1ll Dev1l H1lls Roanoke Sound near Manteo Croatan Sound near Manns Harbor All1gator R1ver near Fort Land1ng Scuppernong R1ver at Columb1a

w z w

~ z z

1) F '!:_/ V 1_/ R F v R F v v F F F r F F R v F R v F R R v R R v R R R R R R

w w z CfJ w w w

R R R R R R R R R v v R F F v F F F F F F F F F F F F v v v R R R

thnd d1rect1on

w ::;: ::;:

~ ::;:

w (/) (/) ::;: (/)

~ z (/) (/) (/) (/) (/) ::;: ::;: z

R v v v v F F F F F R R R v v v F F F F R R R R R R v v F F R R R R R R R v F F R R R R R R R R v F F F v v R R R R R R F F v v R R R R R R F F v v v R R R R R F F v v v R R R R R v F F F v R R R R R v v v v F F v R R R

liF Fall1ng water levels

~IV Var1able effect

liR = R1s1ng water levels

tiOn values are based on long-term averages of Maysville pan evaporation data (after applymg a 0 7 pan coeffi­cient) The area considered for direct precipitatiOn and evaporation mcludes not only the 480 mi2 of Albemarle Sound proper, but also 453 mi2 of open-water area mclud­mg Cumtuck Sound and the lower parts of the North, Pas­quotank, Little, Perqmmans, and Alligator Rivers (the open-water area of the Chowan River IS not mcluded m the total) Inflow from land areas other than the Chowan and Roanoke nver basms (Item E m table 4 2) mcludes dram age from the Albemarle-Pamhco pemnsula to the south, the land area to the north of the sound extendmg mto VIrgima, and a small part of the Outer Banks to the east (total of 2,817 mi2

) The mflows from the Roanoke River basm were based on extensions to the mouth of long-term Geological Survey streamflow records of the Roanoke River at Roanoke Rapids (sta 02080500 on pi 1) It IS Important to note here that the Roanoke River IS regulated by a number of reservOirs m the basm, notably Kerr Lake and Roanoke Rapids Lake (pi 1) These may be controlled to mitigate floodmg and ensure adequate flow dunng drought Inflows from the Chowan River basm were generated by extendmg to the mouth Geologi­cal Survey records from the Blackwater River near Frankhn, Va , and Potecasi Creek near Umon, N C (stas 02049500 and 02053200 on pi 1)

As presented m table 4 2, February IS the month of maximum outflow from the sound and October IS the month of mmimum outflow The latter observation IS m some contrast to the situation m Pamhco Sound, where mmimum outflows occur m June, the month when evap­oration rates are greatest Because of the smaller size of

82 Hydrology of MaJor Estuaries and Sounds of North Carohna

Albemarle Sound and Its relatively greater mflow, com­pared to Pamhco Sound, evaporation does not play as large a role m Its water budget However, dunng times of mmimum precipitatiOn and very low freshwater mflow, evaporation can be the largest Item m the water budget of the sound Figure 4 4 shows estimated low-flow frequency relations for 7- and 30-day penods for all mflow from the 17,426 mi2 area tnbutary to Albemarle Sound These rela­tions are similar to those developed earher for Pamhco Sound and do not account for mflow due to direct precipi­tatiOn on Albemarle Sound and Its associated open-water areas If the mimmum 30-consecutive-day 50-year mflow of about 1,500 ft3/s were to occur m June of a given year, and If we further assume that precipitation IS negligible for the month, while evaporation IS average (4,200 ft 3/s from table 4 2), then the net outflow to Pamhco Sound for that month would be negattve, that ts (0 + 1 ,500-4,200) ft3/s, or -2,700 ft3/s A negative value such as this mdicates that there IS a net mflow at this rate from Pamhco Sound to Albemarle Sound through Croatan and Roanoke Sounds

High-flow frequency curves are also of mterest be­cause they give an mdicatiOn of the amount of flushmg that may take place m Albemarle Sound dunng the late wmter and early sprmg (fig 4 5), and this IS an Important factor m hmitmg algal blooms For example, the maximum 30-consecutive-day 1 0-year average mflow from areas tnbutary to Albemarle Sound IS about 64,000 ft3/s At this rate, the volume of mflow would be equal to the volume of Albemarle Sound (5,310,000 acre-ft) m lUSt 6 weeks, compared to the 14 weeks reqmred for m­flow to Pamhco Sound to equal the volume of the sound at the 30-day 1 0-year flow level

7 1-w w LL ----- Chowan Rrver near Edenhouse

6 z ----Albemar le Sound neor Edenton

.. . ......... Pasquotank River at Elrzabeth City 1-

5 :r: .··. <.::>

w :r:

4 w <.::> <1: <.::>

3

a:: 30 ::::::> 0 :r:

a:: 20 w Cl..

(f)

10 w _.J

~

z 0

a w w 10 Cl.. (f)

a z 20 :it 27 28 29 30 29 30 2 3

JULY 1960 NOV I 960 DEC 1960

Figure 4.3. Wind speed at Elizabeth City and water levels at Chowan River near Eden house, Albemarle Sound near Edenton, and Pasquotank River at Elizabeth City, July 27-30 and November 29-December 3, 1960. Water level records are from tide gages operated by U.S. Army Corps of Engineers.

0 z 0 u w (./)

0:: w a_

I-w w LL

u rn ::_)

u

z

w <..9 0:: <t I u (./)

0

5000

4000

3000

2000

1000

0 0 .01

Drainage area is

1.1

~ ~ "' ~ ~ ),

' ~ ~ Jo 17,426 mi 2 r'-4y

~~ ~ ?,D ?----~ r--r-o 4y ~ ~ r-o

15 2 3 4 5 10 20 YEARS

30 40 50 RECURRENCE INTERVAL, IN

100

Figure 4.4. Minimum 7- and 30-consecutive-day average inflow to Albemarle Sound from land drainage (not adjusted for precipitation on and evaporation from open-water areas) .

Hydrology of the Albemarle Sound Estuarine System 83

= ~ :I

"< c. a ~ s. § 0 .. !I' 2' Dol .. ; Cl>

Dol :I c. ~ c :I

li­s. z 0 :::1 :::r Q 2.. 5 Dol

Element of Gross water budget

A Precipitation on Albemarle Sound and associated open-water areas

B Evaporation from Albemarle Sound and associated open water areas

c Inflow from Chowan River Estuary at mouth near Edenton

D Inflow from Roanoke River Estuary at mouth near Plymouth

E Inflow from land areas not included in above elements

F Total outflow of Albemarle sound into Pamlico Sound F = A - B + C + D + E

Table 4.2. Monthly and annual gross water budget for Albemarle Sound

Drainage Average monthly and annual values, in cubic feet per second area in

square Average miles Jan Feb March April May June July Aug Sept Oct Nov Dec annual

933 2,800 3,400 2,900 2,500 2,800 3,600 5,400 5,000 4,300 2,500 3,000 2,600 3,400

933 1,000 1,700 2,200 3,400 3,900 4,200 4,100 3,500 2,800 1,800 1,400 900 2,600

4,943 6,500 9,100 8,600 6,600 3,700 2,600 3,000 3,500 3,000 2,200 2,500 4,400 4,600

9,666 10,000 12,000 10,000 11,000 10,000 8,500 8,000 7,500 6,500 6,500 7,500 8,300 8,900

2,817 4,200 5,900 5,600 4,300 2,400 1,700 1,900 2,200 2,000 1,400 1,600 1,300 2,900

18,359 23,000 28,000 25,000 21,000 16,000 12,000 14,000 15,000 13,000 11,000 13,000 16,000 17,000

L__ __ - -- -- '--- ---

a :z 0 u w (/)

0:: w a_

1-w w LL.

u co ~ u

:z

w (.!)

0:: <(

:::I: u (/)

a

300,000

200,000

100,000

0

Dramage area 1s 17,426 m12

~ ~

~ ~ I

r

1 ,/

/ ~

~" vo" .~

~( ~

~

30- D A'( -<

I 01 I I 15 2 3 4 5 10 20 30 40 50 100 RECURRENCE INTERVAL, IN YEARS

F1gure 4 5. Max1mum 7- and 30-consecutlve-day average mflow to Albemarle Sound from land dramage (not adJUSted for pree1p1tat1on on and evaporation from open-water areas)

Extent and Duration of Saltwater Intrusion

The sahmty of Albemarle Sound IS usually at a mm­tmum m March as a result of heavy spnng runoff dtsplac­mg sahne water seaward, and IS at a maxtmum m De­cember, after relatively low freshwater mflows dunng the summer and fall have allowed saline water to agam ad­vance landward (ftgs 4 6 and 4 7) Although values gtven are for the water surface, the mtxmg effects of tides and wmds are usually sufficient to prevent any stgmftcant sa­hmty stratification m the open sound and surface-to-bot­tom mcreases seldom exceed 2 or 3 percent Not only Is Albemarle Sound generally less sahne than Pamiico Sound, but the seasonal vanatwns m Its sahmty are less than m Pamiico Sound The seasonal pattern of saltwater mtruswn m the Albemarle Sound near Edenton (sta 02081155 on pi 1) IS also evident from the spectftc con­ductance data m ftgure 4 8

The extent and duratiOn of saltwater mtruston mto the estuanes of Albemarle Sound ts a subJect of tmpor­tance because many of these estuartes represent potential sources of water for mdustnal and agncultural uses and are (or m some cases may be) smtable nursery areas for a vanety of commercially valuable shellfish and fmfish The U S Geological Survey determmed daily specific conductance of water at nme stattons m the Albemarle Sound estuanne system (pi 1) for variOus time penods between October 1954 and December 1968 (table 4 3) m order to determme the extent and frequency of saltwater

mtruswn m the sound and Its tnbutanes These statton data were supplemented by numerous spectftc conduc­tance and chlonde determmatwns made of water samples from a large number of other locations, these were used to help define the 2-year maximum upstream extent of saltwater mtruswn (water contammg 200 mg/L chlonde) under nonhumcane condttions, as shown on plate 1

Ftgures 4 9-4 15 from Wtlder and others (1978) show the duratiOn of mtruswn of saline water at seven of the nme stations on plate I In many cases, separate dura­tion curves are shown for the enttre penod of record and for the years of maxtmum and mtmmum saltwater mtru­ston

The mformatwn contamed m these conductance du­ration curves should be useful m planmng for posstble use of these estuanes for water supply Although the quanttty of water available at most of these locatiOns ts virtually unhmtted, the relations show that the water ts bracktsh for at least part of most years Thus, the water at these loca­tions would then almost certamly be unsUitable for public water supplies because chlonde concentratiOns would ex­ceed the Environmental Protection Agency's recom­mended upper limits of 250 mg/L

The largest cities near the Sites named m 4 9-4 15-among them Elizabeth Ctty, Hertford, Columbia, and Edenton-presently denve thetr water supplies from wells However, mdustnes whtch may locate m these areas and whtch reqmre large amounts of water for mdus­tnal use may, dependmg on the mdustry, find nearby es-

Hydrology of the Albemarle Sound Estuanne System 85

0 10 20 30 4() 50 60 I( ILOMETERS

EXPLANATION ---8--- SALINITY, IN GRAMS PER KILOGRAM (Seawater contams about 34 5 grams of dlSSOlved sohds per kilogram of seawater ) Salinity tnterval variable

Figure 4.6. Average surface salm1ty of water m Albemarle Sound and v1cm1ty dunng tt1e month of March (Mod1f1ed from W1ll1ams and others, 1967 )

tuanne water of acceptable quahty Although the water quahty needs of mdustnes vary, and no cntena will fit all mdustnes, water With a chlonde concentration of 500 mg/ L (as mdicated by a conductance of about 1,900 1:1-mhos) IS unsUitable for many mdustnal uses On the other hand, water that meets dnnkmg water standards (less than 250 mg/L chlonde) Is acceptable for many uses, although some users may reqUire treatment of the supply

THE CHOWAN RIVER ESTUARY

The 50-mtle-long Chowan River, which occupies a drowned nver valley, Is formed by the confluence of the Blackwater and Nottoway Rivers JUSt north of the North

86 Hydrology of MaJor Estuar~es and Sounds of North Carohna

Carolina-VIrgtma state hne (pl 1) From here, It flows generally south and empties mto the western end of Al­bemarle Sound near Edenton Upstream from Hohday Is­land (fig 4 16) extensive swamps border the estuary, downstream, the estuary widens considerably and Is more than 2 miles wide m some sections The average depth of the estuary IS only about 12 feet Two Important tnbutanes, the Mehemn and Wiccacon Rivers, enter the estuary from the west

Discharge from 3,098 mt2 of the total of 4,943 mt2

dram age area ts gaged From records at gaged pomts, the average flow of the Chowan Rtver at the mouth IS es­timatd at 4,600 ft3/s, or about 0 94 (ft3/s)/mi2

The estuary IS affected to some degree by ocean ttdes throughout tts 50-mtle length, although tide ranges are less than 1 foot m most locatiOns The mfluence of

0 5 10 20 30 40 MILES

0 10 20 30 40 50 60 KILOMETERS

EXPLANATION

-----4 -- SALINITY, IN GRAMS PER KILOGRAM (Seawater contams about 34 5 grams of dissolved sohds per kilogram of seawater ) Salm1ty mterval vanable

Figure 4.7 Average surface salrn1ty of water rn Albemarle Sound and VICinity durrng the month of December (Mod1f1ed from Wrllrams and others, 1967)

ocean tides extends up mto the lower parts of all tnbutanes to the Chowan River, mcludmg the Nottoway and Blackwater Rivers (fig 4 16 and pl 1)

W mds are usually more Important than lunar tides and freshwater mflow m affectmg water levels and short­term circulatiOn m the Chowan estuary Wmds sometimes cause as much as 4 feet vanation m water levels (Dame), 1977)

Saltwater mtrus10n mto the Chowan estuary does not occur frequently Chlonde concentrations are usually less than 50 mg/L, even at the mouth, except when un­usual weather conditions force sahne water out of Pamhco Sound mto Albemarle Sound or when the ocean washes across the narrow hamer Island at the east end of Al­bemarle Sound Several factors contnbute to the mfre­quency of saltwater mtrusion under normal conditions

First, the Chowan Rtver ts far removed from the ocean, the nearest direct oceamc connection ts at Oregon Inlet, about 70 mtles from the mouth of the Chowan Also, freshwater flows are sustamed dunng dry penods by re­leases from reservOirs on the Roanoke Rtver and they usu­ally prevent saltwater from advancmg mto the Chowan and Roanoke estuanes

Present water uses of the Chowan estuary mclude mdustnal water supphes, bathmg, boatmg, fishmg, and other forms of recreatton, commercial ftshmg, particularly for hemng, rockfish, catfish, and white perch, and ag­ncultural uses, mcludmg hvestock watenng and trrtgatton At present, all domestic water supphes m the North Carohna part of the basm are denved from ground water

Algal growth m the Chowan Rtver has at ttmes caused severe problems It first reached nutsance propor-

Hydrology of the Albemarle Sound Estuarme Svstem 87

Table 4.3. Max1mum chlonde concentrations and spec1f1c conductance of water at dally samplmg stat1ons m the Albemarle Sound estuanne system (B) md1cates bottom sample See plate 1 for locat1ons

Maximum Max1mum Station Period of chloride conductance Name concentration No. record

1n mill1grams 1n m1cromhos

02043852 Pasquotank R1ver Oct. near Elizabeth Sept. C1ty, N. c.

02043862 Pasquotank R1ver Oct. at El1zabeth Sept. C1ty, N.C.

02043892 Perquimans R1ver Oct. at Hertford,N.C. Sept.

02050160 Chow an River Oct. near Eure, N.C. Dec.

02053244 Chowan R1ver Oct. at W1nton, N.C. Sept.

02053652 Chowan R1ver Oct. near Edenhouse, Sept. N.C.

02081155 Albemarle Sound Oct. near Edenton, Sept. N.C.

02081166 Scuppernong River Oct. near Creswell, Sept. N.C.

02081172 Scuppernong River Oct. at Columbia, Sept. N. c.

twns m the summer of 1972, when extensive blooms se­verely hmited the use of the nver for commercial and sport fishmg, recreatiOn, and navigatiOn Although the Chowan River naturally contams sufficient mtrogen and other nutnents necessary for algal blooms, the rather se­vere conditions which existed m the summer of 1972 and agam m the summ(ir of 1976 may have been caused by m-

88 Hydrology of MaJor Estuar~es and Sounds of North Carohna

per l1ter

57- 1,940 67 Oct. 15, 1961

57- 8,020 (B) 67 Oct. 30, 1958

57- 1,290 60 Dec. 25, 1958

67--

68

54- 398 67 Dec. 15, 1958

57 9,140 (B) 67 Nov. 11, 1958

57- 12,100 (B) 67 Nov. 3-6,

1958

59- 2,270 67 June 18, 1967

63- 2,980 67 June 5, 1967

25°C

6,380 Oct. 15, 196

20,800 (B) Oct. 29, 195

4,290 Dec. 25, 196

880 ~mho Dec. 19, 196

1,400 Dec. 13 and 15, 1958

23,500 (B) Nov. 11, 195

30,600 (B)

7,260 June 18, 196

9,300 June 5, 1967

1

8

8

s 7

8

7

creased nutnent loadmg from a fertilizer plant near Tums, from mumcipal wastewater discharges, and from runoff from agncultural areas The discharge from the fertilizer plant was stopped by State action soon after the 1972 bloom, but It was discovered that high mtrogen water was seepmg from the ground around the plant at about the ttme of the 1976 bloom (Stanley and Hobbie, 1977)

u 5000 0 l(")

N z

t-<[ 4000

w u a:: z w

t-<[ w t- ~ 3000 u :::::> t-0 z z w 0 u 2000 u

a:: u w

a_ u.. 1000 (./) u

0 w a_ :r:: (./) ~

0 0 a:: FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC u JAN :E

Fagure4.8. Average monthly spec1f1c conductance of Albemarle Sound near Edenton, 1957--67

I 2 5 10 20 50 80 90 95 98 99

\ u 0 ' I I I L1"l N

E-< -~ w u~

~~ 1000 E-<W Ul: ;::JH OH

1\ Example

\ SpecifiC conductance exceeds 800 about 6

~-"" ..... percent of the t1me ~ \. \ I I I I I I

zz ow uu

l 1

' Curve based on 3622 dOlly r-uo:; HW ~p... H UCI) WO

l. observations for the per1od

\ Oct 1957 to Sept 1967 r-

Bl~ 0 \ c::<: u H 100 l: ' -"""" z H ~ - .....

I 2 5 10 20 50 80 90 95 98 99

I 200

880

310

250 200

145 120 90

65

40

c::<: w E-< H ...< c::<: t:Ll p...

C/)

~ C,!) H ...< ...< H l:

z H

w~

0 H c::<: 0 ...< ::c u

10,000

:;.; L1"l N

H -~ w

uc::<: ~~ E-<W u;;:: ;::JH

~~ ow 1000 uu u~ HW ~p... H UCI) WO

Bl~ 0 c::<: u H l:

z H

100

I 2 5 10 20 50 eo 90 95 98 99

" ' JJ. U.l J, 11 Jy L ' bottom observot1ons for the= ....... per1od Oct 1957 to Sept 1967-~ '

""'" ~ 1 _l i 1 1 1 1

' \ Curve bosed on 3619 dolly_

\ ~ surface observot1ons for

'\ ' the per 10d Oct 1957 to-1\ Sept 196 7

~ \ \

''" ~ / \

1\ \ / ' f- xomple / \\

Specd1c conductance ~ r- exceeds 800 about 36

~I. percent of the t 1 me

I I I I I I I -- ...... --I 2 5 10 20 50 80 90 95 98 99

7ZOO

3250

2530

1850 ~ 1500 H

H

1200 ...<

880

310

250

200

I I 45 20

90

65

40

w 0 H 0::: 0 ...< ::c u

PERCENTAGE OF TIME SPECIFIC CONDUCTANCE OR CHLORIDE CONCENTRATION IS EQUAL TO OR GREATER THAN A GIVEN VALUE

Fagure 4.9. Cumulative frequency curve of spec1f1c con­ductance and chlonde, Pasquotank R1ver near Elizabeth City (sta 02043852 on pi 1) (From Wilder and others, 1978)

Fagure 4.10 Cumulat1ve frequency curves of specifiC con­ductance and chlonde, Pasquotank R1ver at Elizabeth City (sta 02043862 on pi 1) (From Wilder and others, 1978 )

Hydrology of the Albemarle Sound Estuarme System 89

I 2 80 90 95 98 99 5 10 20 u 0

u 0

Ll'"\ N

E-< -< w

ur:.:: ~~ 1000 E-<W Ul: :::>H

~~ OW uu ur:.:: HW .... p,. H Utll WO

el~ 0 r:.:: u H 100 l: z H

~ JJp1l I 1'\ Spect ftc conductance

1\ exceeds 800 about 19E 1_ercent of the t1~e r-

"'-"" r-

I I \ Curve based on 1092 dotly _\ observations for the -

pertod Oct 1957 to Sept ,_ I\ 1960

"f' ~ r-...

,......

880 r:.:: Ll'"\

w N

310 E-< E-< H -< ...J w r:.:: ur:.:: w ~~ p,.

t;~ 250 til :::>H 200 ~ ~~

145 OW c.:> uu 120 H

...J ur:.:: 90 ...J HW H .... p,.

l: H 65 z Utll

wo H el~ 40 w~ 0

r:.:: c:l u H H r:.:: l: 0 ...J z ::r: H u

I 2 5 10 20 50 80 90 95 98 99

I 2 5 10 20 50 80 90 95 98 99

I'-Curve bo~ed 1

o1n 3576 do

1ily

1- r-

' 1\. bottom observoltons for the- r-

i\ \ Vpertod Oct 1957 to Sept 1967 r-

1000

1\ K E 1xo~plle I

'f \ Spec1f1c C

1

0nductonce exceeds 800 about 18 percent of the ltme r- -

I ~ I

If ll I 1

100

.I based on \ f-Curve 3578 dolly sur-'

t-foce observo-

1\ !tons for the per1od Oct 1957 1\ r--to Sept 1967

I l l_ C"''o I I 1 J r""ooo.

I I -,..._ I 2 5 10 20 50 80 90 95 98 99

2530

1850 1500 1200 880

310

250 200 I 45 120 90 65

<40

~ c.:> H ...J ...J H l: z H

PERCENTAGE OF TIME SPECIFIC CONDUCTANCE OR CHLORIDE CONCENTRATION IS EQUAL TO OR GREATER THAN A GIVEN VALUE

Ftgure 4.11. Cumulat1ve frequency curve of speetflc con­ductance and chlonde, Perqu1mans R1ver at Hertford (sta 02043892 on pi 1) (From Wilder and others, 1978)

I 2 5 10 20 50 80 90 95 98 99

Curve based on 3614 dolly bottom observot1ons for the : 3250

u l-i-+-+''~,-+-'"/pertod Oct 1957 to Sept 1967 : 2530 ~ ~ ~-4-4-~vr-~+-+-~~-1--~-T--r-~ 1850 H N ~~~+-~--~~~~-+~--4--+--r-~1500 ,..J

E-< 1-4-+~~~-'~'~~~~4-+-1--1--+-~-r~ 1200 ~ w· < I' \ Example ----------+---i 88o P..

~ ~ \l\ Spec1f1c conductance ; """' w I) exceeds 800 about 43- 310 ~ Ul: c.:> ~ ~ ~ percent of the ltme ~ OW ~ /v ~ u u IOOOE~~~~~~~,~~l/§!~~~~~~~250 l: u r:.:: r=. Curved based on 3-LI.. L z ~ ~ r-3611 dolly surface ~ 200

H

ti til r-observattons for _) 145 w ~ ~ ~the pertod Oct 1957---411l~-+--+-+-4--+-+--1 ~~0 ~ ~ to Sept 1967 1\ ~ ~ 1------------------f--l\t--~,_+--1--+-~-+_, 6 5 a l: z H

~~--+-~--~+-~~1~\_,--~--+--r-~ 40

100~4-~~-4-+~~~~~~-4--1--~-f _:"''o 1--+--+--t--t-- ·-r- -r-~

I 2 5 10 20 50 80 90 95 98 99

Ftgure 4 12. Cumulative frequency curves of spec1f1c con­ductance and chlonde, Chowan R1ver near Eden house (sta 02053652 on pi 1) (From W1lder and others, 1978)

u 0

Ll'"\ N

I 2 5 10 20 50 80 90 95 98 99 ~~ro-.-.--,-,-,,-,-,-,--,~-~~-. 1200

' I I I I 880 ~ t--+-t,----+-4-- Exam pIe ~~r--+--i----t--t-1 310 H

~ Jv ...J Specd1c conductance r:.:: exceeds 800 about 5 ~

IOOOt=:t=t::::j~+:=t percent of the t1me -r--r-- 2so ~ ..1 ...1 I I -r-r- 200 ~

~~~11~\+--+-+-1 +-1 ~f--1~_,~~-r-+1--+-~ 145 c.:> _\ I I I I I H

1--i--+--+-'~,- Curve based on 2871 dolly r- 120 j 1\ observottons for the pertod r- 90 ~

1--i--+--t--~H\r- Oct 1959 to Sept 1967 r- 65 ;5

~~f--4--+~,d-+-+-~f----1_,~-r-+--+-~ 40 w

'~ .... ~ ~ IOO~~==~=t==t=i=i=~~~~~~~~==~~ 5

I 2 10 20 50 80 90 95 98 99

PERCENTAGE OF TIME SPECIFIC CONDUCTANCE OR CHLORIDE CONCENTRATION IS EQUAL TO OR GREATER TILAN A GIVEN VALUE

Ftgure 4.13. Cumulative frequency curves of speetf1c con­ductance and chlonde, Albemarle Sound near Edenton (sta 02081155 on pi 1) (From W1lder and others, 1978)

90 Hydrology of MaJor Estuanes and Sounds of North Carohna

Figure 4.14. Cumulative frequency curve of speetflc con­ductance and chlonde, Scuppernong R1ver near Cresswell (sta 02081166 on pi 1) (From W1lder and others, 1978 )

10,000

u 0

11'1 N

1000

100

I 2 5 10 20 50 80 90 95 98 99

.......

"""""' """""' ..........

""""" ' " :\ \ \ ....

- ~ \ Example ~ \ - Spec1f1c conductance \ ,.....

exceeds 800 about 81 \ ~ percent of the t1me

' I I I l I I I 1 I I_ I I __ 1 I

Curve based on 594 dolly

~ observations for the per1od H- Oct 1965 to Sept 1967

I ' I I I I I I I I I ~

I 2 5 10 20 50 80 90 95 98 99

3250

2530

1850 1500 rx: 1200 ~

H 880 ....:l

rx: w

310 p..

~ 250 ~

200 j 145 120 90

65

40

H ~

z H

PERCENTAGE OF TIME SPECIFIC CONDUCTANCE OR CHLORIDE

CONCENTRATION IS EQUAL TO OR GREATER THAN A GIVEN VALUE

Fagure 4.15 Cumulative frequency curve of spec1f1c con­ductance and chlonde, Scuppernong R1ver at Columb1a (sta 02081172onpl1) (FromWIIderandothers,1978)

Water Levels

Short-term water level changes m the Chowan es­tuary are caused pnmanly by wmds, wtth lunar ttdes and freshwater mflows of lesser Importance Generally, wmds from the southeast tend to cause htgher water levels m the estuary, and wmds from the northwest cause lower water levels, as Illustrated m figure 4 17 for two locatmns-near Eure and near Edenhouse Rtsmg water levels at both lo­cations on December 7 and 8, 1974, were caused by southerly wmds, and falling water levels on December 9 and 10 were caused by northerly wmds The semtdmrnal tide cycles are also evtdent m ftgure 4 17 Due to funnel­mg effects of the narrowmg channel, ttde ranges are actu­ally greater at the upstream station (Eure) than at the downstream statton (Edenhouse) Apparently, these fun­neling effects more than compensate for the tendency of the tide wave to dte out due to loss of momentum as tt propagates up the estuary

These funneling effects are even more apparent m ftgure 4 18, which shows contmuous water-level records for five gagmg stations dunng a penod of little wmd ef­fect on December 6, 1974 The mcrease m ttdal range m the upstream dtrectton ts apparent As mdtcated by the time lag m ftgure 4 18, the passage of htgh or low ttdes through the estuary from the mouth near Edenhouse to near Eure, a dtstance of about 45 5 miles, takes about 2 hours

Analysts of water-level data from an earlier study at the same two locattons (Jackson, 1967) reveals an mter­estmg annual cycle m water levels (fig 4 19) Monthly average water levels m the Chowan Rtver estuary near Eure and Edenhouse follow a sme-like pattern, with highs m the summer and lows m the wmter This ts nearly the opposite of the effects of normal runoff patterns m upland streams, whtch produce htgh water levels m late wmter and early spnng and low water levels m the summer and fall The annual water-level pattern m the Chowan estuary was attnbuted by Dame] (1977, p 32) to the seasonal pat­tern of the prevathng wmds m the area, whtch are gener­ally out of the north and northwest m the fall and wmter, resultmg m lower water levels, and out of the south and southwest dunng the summer, resultmg m htgher water levels The seasonal range m water levels thus produced ts about 0 8 foot at both stattons

Flow

Usually, short-term flow In the Chow an estuary ts mfluenced pnmartly by wmds, lunar ttdes, and freshwater mflow, m that order of tmportance Only durmg penods of htgh runoff ts freshwater mflow of greater stgmficance than lunar tides and wmds at a gtven moment Long-term flow IS, however, determmed pnmanly by the rate of freshwater mflow

Freshwater mflow to the estuary from all sources averages about 4,600 ft3/s [0 94 (ft3/s)/mt2

] and the esti­mated monthly dtstnbutton of average mflow, m cubtc feet per second, ts as follows

January 6,500 July 3,000 February 9,100 August 3,500 March 8,600 September 3,000 April 6,600 October 2,200 May 3,700 November 2,500 June 2,600 December 4,400

V anabtlity m annual mean mflows ts caused pnmar­Ily by year-to-year variations m prectpttatton Thts varia­bility IS reflected m the discharge-probabthty relatton shown m figure 4 20 Although thts relation was de­veloped on a per-square-mile basts for the combmed dramage of 2,060 mi2 represented by the Blackwater Rtver near Frankhn, Va , and the Nottoway Rtver near Sebrell, Va , the relatiOn may be applied with useful accu­racy to the enttre 4,943 mt2 dramage area of the Chowan River basm

Because penods of low freshwater mflow to the Chowan estuary are times of cnttcal water supply and be­cause the lack of flushmg of the nver at such times ts one of the condtttons that favors nmsance algal blooms, data on these penods are of great mterest Ftgure 4 21 shows combmed low-flow frequency curves for the Blackwater

Hydrology of the Albemarle Sound Estuarme System 91

30'

20'

0 I

0

7JOOO'

EXPLANATION

[] SWAMP

so'

VIRGINIA

NORTH CAROLINA

EURE #

02053633

A STAGE RECORDER

2 3 4 5 10 MILES ~

02053 2 5 10 15 KILOMETERS

EDEN HOUSE I#

7JOOO' 50' 76°40'

Figure 4.16. Chowan River, major tributaries, and adjoining swampland. (From Daniel, 1977.)

92 Hydrology of Major Estuaries and Sounds of North Carolina

20'

AVERAGE DAILY WIND SPEED AND DIRECTION, IN MILES PER HOUR AT CAPE HATTERAS, N C

9 5 7 7 13 7 II 8 10 5 4 5 4 6

I \ I WIND /

-- DIRECTION

200~----------,_-----------+------------~----------~-----------+------------+-----------~

1-w w LL.

CHOWAN RIVER NEAR EURE 02050160 ~

INFERRED wiND EFFECT NEAR EURE

RIVER NEAR EDENHOUSE -,INFERRED WIND EFFECT

NEAR EDENHOUSE

SEA LEVEL

12-6-74 12-7-74

02053652

12 8-74 12-9-74 12-10-74 12-11-74 12-12-74

Figure 4.17. Contmuous water-level records for Chowan R1ver near Eure and Chowan R1ver near Eden house for December 6-12,1974 (From Damel, 1977)

River near Frankhn, Va , and the Nottoway River near Sebrell, Va

Some low-flow regulation does take place on tnbutanes to the Chowan estuary Umon Camp Paper Company, which ut1hzes ground water for Its process water, did at one time discharge pulp mill wastes mto the Blackwater River contmuously, but smce 1964 wastewater has been stored and discharges limited to wmter months only, when freshwater mflows are high However, the City of Norfolk, Va , does divert some water from the Black­water and Nottoway Rivers to augment Its mumctpal sup­ply, but the effects of these diversiOns on low flows m the Chowan River have not yet been evaluated

Damel (1977) discussed a one-dimensiOnal deter­miniStic flow model of the Chow an River based on the con­tmmty equatiOn The model was developed by the Geologi­cal Survey to generate estimates of dmly flow through a number of nver segments for use m a water quahty manage­ment model The outflow from each segment was computed from an expanded form of the contmmty equation

Q,=Q,_ 1 +I,+P, -E, -ET, ± ~S, (4 I)

where Q, Is the outflow from segment z, Q,_, IS outflow from the adJacent upstream segment, I, IS the lateral mflow from

the ungaged dram age area apportiOned to segment 1, exclu­SIVe of the dramage area w1thm segment z, P, IS the precipita­tiOn that falls directly on segment 1, E, IS the evaporatiOn from the open water surface m segment 1, ET, IS the evapotranspi­ration from the swampland m segment 1, and ~S, IS the change m storage m segment 1 (a falhng stage contnbutes to a positive Q,) Once calculated, the outflow, Q, from any segment becomes the mflow, Q,_ 1 , to the next downstream segment Because flows w1thm the Chowan and the lower reaches of Its tnbutar1es are tide-affected, flows occur m both upstream and downstream directiOns By conventiOn, up­stream flow IS md1cated by a negative sign, downstream flow IS positive

Summaries of generated flows through two of the seg­ments are shown m figure 4 22 for the penod Apnl 1974 through March 1976 At Eure, the most upstream station, m1mmum daily average discharges for each month were often near zero, but no large net upstream flows occurred Near Edenhouse, at the mouth, the mmtmum datly average dtscharge for each month was upstream for all months except one This IS mdtcative of the mcreasmg mfluence of wmd and lunar ttdes m the more downstream segments of the Cho­w an estuary

The average discharge at the mouth near Edenhouse for the 2-year penod was calculated to be 5,800 ft3/s, or about 26 percent greater than the long-term estimated aver­age discharge of 4,600 ft3/s Above-average discharge was expected because of above-average ramfall for the Apnl 1974-March 1976 penod

Hydrology of the Albemarle Sound Estuarme Syst£>m 93

_J

w I 20 > w _J

<! w Cf)

z <! I 00 w ::E

w > 0 CD <!

~ 0 80 w w LJ...

z

-w (!)

<! ~ 0 60 Cf)

040~~~~~~--~~-L~-J--~~~~~--L-~~~~--L-~~~

2400 0600 1200 1800 2400 TIME, IN HOURS

RIVER MILES ABOVE RIVER CHOWAN RIVER WIDTH,

STATION NAME AND NUMBER NR EDENHOUSE IN FEET

I. Chowan Rrver nr Eure 02050160 (FIG 4 16} 45 46 480 2 Chowan Rrver at W 1 n ton 0 2 0 5 3 2 44 35 49 800 3. Chow on Rrver nr Horrellsvrlle 02053573 22 29 1620 4 Chow an Rrver nr ColeraJn 02053633 II 38 8900 5 Chowan Rtver nr Edenhouse 02053652 0 00 8650

Figure 4.18. Contmuous water-level records for f1ve gagmg stat1ons on the Chowan R1ver for December 6, 1974 (From Damel, 1977 )

94 Hydrology of MaJor Estuar1es and Sounds of North Carohna

~ 0 400

I

CHOWAN RIVER NEAR EURE

co cor<> o <:T a> a> _ a> 1.0 r- a> a> w- - 10 co <:T r- a> 1.0 <:T r- 10 RESULTANT MONTHLY WIND SPEED 0 - N r<> N 10 <:- <.0 <:- <.0 - 0 0 - co N N <:- N - r<> r<> N - 0 ( MILES PER HOUR )

t ...-/ I / I I /DIRECTION ! \ \ "'-.. ._! "')( I ! "--'\ \ \ J

Mean 087--

J F M A M J J

1966 A S 0 N

Mean 0 60 --

04

Mean annual woler level

JF MAMJ JASON OJ FMAM J JA S 0 N 1967 1 1968

2 00

I 60

I 20

0 80

0 40

SEA LEVEL

040

f1gure 4.19. Monthly average stages for Chowan R1ver near Eure and Chowan R1ver near Eden house The solid lmes are sme curve approx1mat1ons of the annual cycle of water levels (From Dante!, 1977)

0:: w a_ w 3

_J ....._ ~ w

w 2 u... w 0::

u <:{

::::> co 0 ::::> (f)

u 0::

2 w a_

-w a (..!) 2 a:: 0 <:{ u :r: w u (f)

c.n 0 3 a

Drainage area is 2060 mi 2 , Blackwater R. at Franklin and N tt R t S b 11 0 away . a e re

I Drainage area is 2500 mi 2 at Chowan R.at N.C.-Va . State line f--

I

I I I

_l_ _l I I I I

r- Example. I _1~1 I_ 1 ~ ............ -......... , '--

·~ T ' I I I f- There 1s a 50-percent chance 1n any one --r--

r-

year that the annua I mean dtscharge will be equal to or less

I I I I

99 98 95 90

than 085(ft 3/s)/mt 2

I I J I I I

80 70 60 50 40 30 20

PROBABILITY, IN PERCENT

-I

I 10 5 2

f1gure 4.20. Frequency curve of annual mean d1scharges, combmat1on of Blackwater R1ver at Fran kim, Va , and Nottoway R1ver near Sebrell, Va (From Wilder and others, 1978 )

Hydrology of the Albemarle Sound Estuarme System 95

.

2 0 r T T 1 T I I I I ' I T l.I.J _J

:::E 10

~ ~

Dramage area of Franklm and Sebrell statrons rs 2060 mr 2

..........____ !II... Dram age area at the N C - Va I me rs 2500 mr 2

~ "- -l.I.J cr c::r ::> 0 en

"' ~~ -"- ""'- """'

-"'OIiiiioi ~ '~ ' ~ " " " ~ ~ ~~ " cr

w ~

0 z " " ' ' ' ~ ~ "'

""''

"' "' ' ~ ~ ~ ~ ~ ~ 0 u w en

a::: 01 w ~

~~ " ~ " ~ ""''~ '"" ~ ~ "' " ""' ~ ~ ~ ~ "' """' "'-. " ' Consecutrve ' ' ' """ """

-

' ~ r\. " ' -

"""-.... ' -~ ~ ' days-

....... w w LL...

u " ~ ~~ ' '--.....

"' ~ " "' " -

' 183

I' " ' "' -

' ~ CD ::> u

"""" ~""' " ~ ~· 120

~

z

w 0 01 <..!)

a::: <l' :I: u

Example "'"' ~ "' There rs a 50-percent chance rn any one ""' year that the mrntmum 7-day mean drscharge

""" ~

60-

wtll be equal to or less than 0 05 (ft 3fs) /mt2 "" ' "" ~ 30-"''ii~

en -0 ' 7 I

0.004 99 98 95 90 80 70 60 50 40 30 20 10 5 2 05

PROBABILITY, IN PERCENT

Figure 4.21. Low-flow frequency curves of annual lowest mean d1scharge for md1cated number of consecutive days, combi­nation of Blackwater R1ver at Franklin. Va and Nottowav R1ver at Sebrell. Va (From W1lder and others, 1978 )

Water Quality

Chowan River water at times IS highly turbid due to suspended matenal and IS strongly colored from humic matenal A maximum color umt value of 320 has been measured at the Chowan R1ver at Wmton (sta 02053244 m table 4 4), which far exceeded the 75 umts recom-

96 Hydrology of Ma1or Estuar1es and Sounds of North Carohna

mended by the U S Environmental ProtectiOn Agency (1976) [1977] as an upper hmit for dnnkmg water Iron may also be a problem at times, with values sometimes exceedmg the 0 3 mg/L recommended upper hmit given m the same report However, with proper treatment, water from the Chowan Estuary IS, where not contammated or mixed with saltwater, of acceptable quahty for pubhc, ag­ncultural, and mdustnal use

02050160 Chowan R1ver nr Eure, N C 2 Dra1nage area 2568 m1 2 ~ 30,000r---------------------------~------------~~---------4--------------------------~ a:: Max1mum dally overage ..... (f)

~ 20,000r---------------------------r-----~r-----~-+----~--~---------------------------4 0 0

0 2 0 I------=--....,J16 z ex

~Monthly average o d1scharge

0 w u a:: w .....

M1n1mum dally average d1scharge for each

(f) ~ 10,000~._~~~~--~._~~~~--~~~~~~~~~~~~~~--~._~~~~~--~~~~~

:::>

60,ooo~r-~~r-~~~~~~~~~~~~~~~~~~.-.-.-.-.-.-.-.-.-.-.-.-~

R1ver near Edenhouse, N C

50,000~-----------------------~------------~--------~----­ Dra1nage area 4885 m12 Maxlmum dally average

~ ~ :::> w u ~

d1scharge for each month~ 40,000~------------------------~----+--+--~~--~----~-------------------------4

(f)

~ z ~

w 0 <.!) 0 a:: ex :r u (f)

0

2o,ooo~~~~~~~~~-L-L~~_L_L~~~~~~~~~~~~~~~~~~~~~~~

D J FMA M J JASON D J F MAMJ JASON 0 J F MAM J J A SOND 1 1974 1 1975 1 1976 1

Fagure 4.22 Monthly average d1scharge and max1mum and mm1mum dally average d1scharge of Chowan R1ver near Eure and Chowan R1ver near Eden house (From Damel, 1977 )

Salinity

The Geological Survey operated specific conduc­tance stations on the Chowan Rtver for vanous time penods at three locatiOns-near Eure, at Wmton, and near Edenhouse (table 4 3 and pi 1) To supplement thts pomt data, seven boat runs to determme spectftc conductance at a number of other locatiOns were made between October 7, 1954, and September 27, 1968

These data show that saltwater mtruswn m the Cho­wan Rtver occurs mfrequently The specific conductance at Edenhouse, for example, exceeds 800 IJ.mhos only about 18 percent of the time (ftg 4 12), upstream at Wm­ton and near Eure, the time percentages would be much less The maximum specific conductance near Eure for the penod October 1967 through December 1968, a penod of contmuous record, was 880 IJ.mhos on December 19,

1967 Although this penod of record was short, dis­charges were much below average Thus, It IS hkely that the maximum upstream extent of saltwater mtrus10n m the Chowan estuary under nonhumcane conditiOns would be near Eure Thts conclusion IS strengthened by the fact that the maximum spectftc conductance observed at the more downstream statiOn, Wmton, was only 1,400 IJ.mhos (398 mg/L of chlonde) dunng 13 years of datly sampling (Oc­tober 1954-September 1967)

At low sahmty, mtxmg IS fatrly complete from top to bottom across the Chow an estuary, although mstantane­ous sahmty at such times may be stgmficantly less or more close to the banks or m the adJacent swamps because water moves more slowly there than m the mtddle sections of the nver Thus, at htgh slack water, sahmty may be less near the channel edges than elsewhere Conversely, dunng low slack water, sahmty may be htgher near the channel edges than elsewhere

Hydrology of the Albemarle Sound Estuarme System 97

I.C = :I -< Q.

0 0 ~ sa. ~ .!! Q .. 1"1"1 ~ c Dol .. ~ ~ Q.

~ c :I Q. a Table 4.4. Summary of chem1cal analyses of water samples collected at key stat1ons m the Chowan R1ver basm Chem1cal constituents are m m1ll1grams per ~ hter, except spec1f1c conductance, pH, and color (Adapted from W1lder and Slack, 1971a) ~ :I" n Dol

2. 5 Dol

c: .... 0 cu ... .D

~ g ... r:: "'

:>2053073

:>2052244

Station name

CHWAN RIVER BAS IN

Meherrin River near Severn, N C

Chow an lli ver at Winton, N C ~/

10 cu .... 10

cu CON 10 ... r:: s ... 10 c: .... ...

Q

about 1,120

about 4,200

"0

... co >. c: u 10

0 c: cor:: cu ... c: cu cuco "0.-< ... ::l e 10 0"'" ..... C' cu .... ..: u c:a.cu .... cu

U.!: ... > cu Ill >< 10

"" "' l&l

~ept 195l monthly Max to Min

~ept 195~ Avg

pet 1954 daily Max to Min

~ept 196r Avg

00 Q "' -; X 0 ~ -; ~ ... u "' -; ~ e 2; e

::l ~ ::l I&. e ... ...

10 ~

~ ., e .,

u cu ::l ., ... r:: u c: ... 10 ..... 0 ..... co "0

~ ... .... ., ~ 0

"' .... "'

17 0 77 13 3 2 14 4 0 9 9 03 4 2 1 0 4 1 1 3

13 22 6 3 1 9 7 6 1 9

17 64 11 2 8 47 3 1 4 01 2 9 5 2 5 9

10 20 5 7 1 6 9 3 1 7

.., Dissolved Hardness 0

~ solids as Caco3

I u .... ~ :c 0 I U U cu~ ~ ..... ;::-

.., "" c: ....

0 u 0 ~ O:l:ot'l ., ... e ~ ~ 2; ... "0 g cu u~N ... 10 ~ cu 10 cu ... ... c: cu cu cu

... ... .... 10 u cu ... c: 0 cu "0 "0 10 cu 10 e ., c: ... u 10 ::l .ll ... ... ... ... .<:: ::lU ..... ... cu 0 .... c: .... ., .... .... 10 "'" "00 ::l ::l c: .ll ... 10., .... ., .... 0 0 .... ., ...0 u u co I .... u ... 0 0 u ..... ..... ::l ... 0 0><0 ..... t3 ~ r:: 10

~~~1 ..... ... ::l .c ~

... .c CU.-< 10 I~ u =a 8 CQ "' u 2; "" ..: u

2 3 105 46 9 166 7 1 60 83 20 6 8 0 0 61 15 0 62 5 7 10

8 2 9 3 0 0 7 73 24 1 96 30 31 9 8 4 7 0

3 5 0 20 188 171 36 10 297 7 7 320 84 16 46 7 0 00 40 34 10 0 36 6 0 25 11 1 7 2 9 0 1 4 10 73 65 21 2 93 73 25 5 6 9 6 2

At higher sahmty, stratification becomes more ap­parent Notice from figure 4 12 that the frequency curves for surface and bottom specific conductance seem to merge at values less than about 800 J.Lmhos, while they di­verge at higher values, mdicatmg stratificatiOn

The mverse relation of sahmty at Edenhouse to freshwater discharge IS evidenced by the percentage of

time bottom conductance values exceeded 800 J.Lmhos for the prevailing annual average discharges dunng the years 1958-67 (fig 4 23) Although the relatiOn may be useful for prehmmary estimates of bottom specific-conductance conditions at Edenhouse under vanous conditions of an­nual freshwater mflow, It must be acknowledged that the data pomts have considerable scatter around the hne of re-

1 4 1958 (YEAR)

w _J

:E ~-

w 0 0::: _.J <:( lL :::::> 2 0

en

o:::O:: ww t-CL <(

::r:o :z:Z cnO wu o:::W lJ_U)

w <.!) <(

0::: w > <(

0::: w CL

t-w w lL

u -CD :::::> u

z

1.3

1.2

I I

10

0 9

0.8

07

0.6

0.5

0

0

01962

1961 0

01963

• 10 20

PERCENTAGE OF TIME BOTTOM GREATER THAN 800

1964 0

0 1966

30 40 CONDUCTANCE MICRO MHOS

WAS

50

F1gure 4.23. Percentage of t1me bottom spec1f1c conductances exceeded 800 m1cromhos for vanous annual average dis­charges for Chowan R1ver near Eden house, 1958--67

Hydrology of the Albemarle Sound Estuarane System 99

lat1on Th1s scatter may be due to several factors-the dif­ferences m w1thm-year d1stnbution of d1scharges, year-to­year d1fferences m preva1hng wmd speed and d1rect10n, and vanations m regulation patterns of reservmrs on the Roanoke R1ver wh1ch, as previOusly mentiOned, have a d1rect mfluence on moderatmg saltwater mtruston m Al­bemarle Sound and, md1rectly, mto the Chow an Rtver

THE ROANOKE RIVER ESTUARY

The total area of the Roanoke Rtver basm (pi 1) 1s 9,666 mt2

, the largest of any North Carohna estuary However, only 3,506 mt2 of the dramage hes m North Carolina, the other 6,160 mt2 are m southern Vtrgmta The Roanoke R1ver ongmates m the Valley and R1dge Provmce west of Roanoke, Va , and flows m a general southeasterly dtrectiOn toward the Atlantic Coast, empty­mg mto Albemarle Sound about 7 m1les downstream from Plymouth, N C Pnnctpal tnbutanes mclude the Dan, Fal­hng, Otter, and Blackwater Rtvers The hmtt of lunar ttde effects m the Roanoke Rtver has not been well estab­lished, but IS thought to be near Hamtlton, about 60 m1les upstream from the mouth

The greatest w1dth of the estuary, near the mouth, ts only about 0 3 mile and, upstream from Plymouth, wtdths are about 0 1 m1le or less The narrow w1dth of the Roanoke near the mouth ts m sharp contrast to the Neuse, Pamhco, and Chowan Rtvers wh1ch are several mtles w1de at thetr mouths The lower Roanoke, like the others are now, was once a drowned nver valley Now, how­ever, 1t has been largely f11led by sed1ments Wtthm the delta thus formed ts a fatrly unusual system of dls­tnbutanes (fig 4 24) wh1ch carry some water from the Roanoke mto the Cashte Rtver and, m the case of one large unnamed d1stnbutary, duectly mto Albemarle Sound Max1mum depths along the estuary vary from about 8 to 18 feet A commercial navtgatiOn channel 1s mamtamed m the Roanoke River to Palmyra, 81 miles up­stream from the mouth The channel ts mamtamed to 12 feet deep and 150 feet w1de from Albemarle Sound to about 1 mtle upstream from Plymouth, a distance of 10 miles, thence a channel 8 feet deep and 80 feet w1de to Palmyra, a d1stance of 18 miles

Average annual prectpttatton over the basm ts about 45 mches The average annual outflow of the Roanoke Rtver at the mouth IS about 8,900 ft3/s, second only to the outflow of the Cape Fear Rtver among North Carolina's estuanes

Flow of the Roanoke R1ver 1s h1ghly regulated, par­ticularly by Roanoke Raptds Lake (deta1ls to be d1scussed later) The combmation of relatively h1gh outflow, small cross-sectional areas, and low-flow augmentatiOn by Roanoke Rap1ds Lake, effectively blocks sahne water

100 Hydrology of MaJor Estuar~es and Sounds of North Carohna

from the estuary Dunng 13 years (October 1954-Sep­tember 1967) of daily water sampling at Jamesvtlle (sta 02081094 on pi 1), the max1mum measured chlonde con­centratiOn was only 12 mg/L Three spectfic conductance surveys by the Geologtcal Survey dunng normally low­flow penods (October 6, 1954, July 25, 1957, and Oc­tober 1 , 1957) fa1led to reveal any s1gmficant saltwater en­croachment, even at the mouth Stgmficantly, the survey of October 6, 1954, was made before mcreased low-flow augmentation from Roanoke Rap1ds Lake and at a ttme of record low streamflows m many parts of the State At that t1me, near maxtmum-of-record saltwater encroachments were bemg measured on other estuanes Thus, tt ts not likely that any stgmficant saltwater encroachment wtll occur m the future m the Roanoke River estuary, even under extreme drought conditiOns, as long as the current flow regulation patterns are mamtamed

Flow

Flow m the Roanoke Rtver estuary has not been studted m detatl, thus tt IS not really known what role wmds play m the flow or to what extent the flow IS af­fected by t1des We can mfer that wmds and tides play a lesser role here than m any other maJor North Carolina es­tuary because of the relative narrowness of the channel and the lack of stgmficant funneling effects Conversely, we can mfer that freshwater dtscharges play a relatively larger role because of the greater magmtude of the dts­charges m relatiOn to channel cross-sectiOnal areas How­ever, validatiOn of these mferences a watts conf1rmat10n from water-level records and flow measurements

As prevtously mentiOned, the average annual out­flow of the Roanoke Rtver at the mouth ts about 8,900 ft3

/

s, or about 0 92 (ft3/s)/mt2, but average flows for a gtven

year may range from about 0 50 to 1 50 (ft3/s)/mt2 (fig 4 25) Actually, dtscussion of freshwater mflow to or out­flow from the Roanoke R1ver estuary ts not really mean­mgful except w1thm the context of the extstmg patterns of flow regulation Flow of the Roanoke River IS extensively regulated by Philpott Lake, John H Kerr Reservmr, Roanoke Rap1ds Lake, Leesvtlle Lake, Lake Gaston, and Smith Mountam Lake All of these reservmrs were created pnmanly for hydroelectric power generation, but many also provide for flood control, low-flow augmentatiOn, water supply, and recreatiOn Because It ts the most down­stream of these reservmrs, Roanoke Raptds Lake ts most Important from the pomt of vtew of tts effects on flow m the Roanoke estuary Pursuant to tts license from the Fed­eral Power CommiSSion, the V Irgm1a Electnc and Power Company must mamtam, subJect to spec1al provtstons, m1mmum mstantaneous flow releases from Roanoke Rap­tds Lake (dramage area 8,395 mt2

) accordmg to the fol­lowmg schedule

_.I.IL

~ --- ~ - ---->.lL.._ - ...:JL_-

- - _.L _.:lL - ::JL

- ___j,(_-

.:L --lL Jlt_ -

- __jL_ - ---.-Ill._-

~ ....liL ~ - ~ ~ -

....lL ----~ ~ .....>I.L--~

~ ~

~ ..>oiL - ...IlL

0 I 0 2

2 I

3 4

r N

5

4 I

6 7

5 MILES I I

8 KILOMETERS

Fagure 4.24. D1stnbutary system of the lower Roanoke R1ver

NI1111111Um 111\/antaneow

Month flo11. 111 /t 3 /5

January, February, March 1,000

Apnl 1,500

May-September 2 000

October I 500

November December I 000

Usually, actual releases from Roanoke Raptds Lake far exceed these mtmmum reqmrements, as mdtcated by measured flows of the Roanoke Rtver at Roanoke Raptds (sta 02080500 m pi 1) Gtven below, m cubtc feet per second, are esttmated average monthly outflows at the mouth of the Roanoke Rtver estuary for the penod Oc­tober 1965-September 1975 About 87 percent of these flow amounts are accounted for by controlled releases from Roanoke Rap1ds Lake

January 10,000 July 8,000 February 12,000 August 7,500 March 10,000 September 6,500 Apnl 11,000 October 6,500 May 10,000 November 7,500 June 8,500 December 8,300

The effects of htgh-flow regulation are reflected m the stmtlar averages for January-May, flood flows are stored m the vartous reservOirs and released over long penods of ttme Low-flow augmentation ts apparent from the relatiVely htgh August-November flows, they average about 0 72 (ft3/s)/mt2 compared to only about 0 57 (ft3/s)/ mt2 m the unregulated Chowan Rtver estuary for the same months

Hydrology of the Albemarle Sound Estuarme System 1 01

0::: w a... w

_J 2 t-w ~

w lJ._ w

1 ..... J . . . . .

Drainage area is 8410 mi 2 at site -

0::: ~ - -u <t - ::::> CD 0 ::::> (/)

u 0::: z w a...

----1 -- J I l

I -~-. --- I 1 I I l 1 r~~-~' l

~ Example 1 1~ .. ---~I I I I -I ---- -~ - There IS a 50-percent chance 1n any one I ---

-- ---1-

annual discharge Will be ~

year that the mean w Cl (!) z 0 3 0::: 0 <t u :r: w u (/)

(/)

....__

1 equ~l to less than 0 85(ft 3/s)/mi 2 or

I 1 __l i _1 __l I J __l

99 98 80 70 60 50 40 30 20 PROBABILITY, IN PERCENT

2 10 5 95 90

Cl

figure 4 25. Frequency curve of annual mean discharges of Roanoke R1ver at Roanoke Rap1ds (After Wilder and others, 1978)

The effects of flow regulation are also apparent m the low-flow frequency curves of ftgure 4 26 for the Roanoke Rtver at Roanoke Raptds At lower probabthties of occurrence, the consecutive-day low flows at Roanoke Rapids are much htgher on a per-square-mile basts than are those, say, of the Blackwater and Nottoway Rtvers (fig 4 21 ), also, the expected range of values for a gtven consecutive-day dtscharge ts much less for the Roanoke Rapids statiOn

I 0 r---~---r--

Water Quality

Summartes of the chemical quahty of water at four key sttes m the Roanoke Rtver basm are gtven m table 4 5, mcludmg observed ranges and average values of maJor chemical constituents Iron concentratiOns some­times exceed the 0 3 mg/L upper hmtt recommended by the Environmental Protection Agency ( 197 6) [ 1977] for

a:: w a...

Dramage area at Roanoke Rap1ds 1s 8410 ml 2

w ......__J w w~ LL.

w a::

Uc::x: en=> :::>0 u(/)

za:: w a...

wo (..!)z a::o <tu :I:w U(f) (/)

-+-----+--t--- Cons ec u t 1 v e

Example.

0 I There 1s a 50-percent chance 1n any one t----+-year that the m1n1mum 7-day mean d1scharge

days 183 120

60

30

t----+- w Ill be e q u a I to o r I e s s t han 0 2 5 ( f t 3 Is ) I m 1 2 --~--T+--_ -_ -_ --1__;-_ -----~-tr---7--+--1

004~~--~--~--~--~---~~~--~~-----~--~---~~---~~ 0 99 98 95 90 80 70 60 50 40 30 20 10 5 2 05

PROBABILITY, IN PERCENT figure 4.26. Low-flow frequency curves of annual lowest mean discharge for md1cated number of consecutive days, for Roanoke R1ver at Roanoke Rap1ds (After Wilder and others, 1978)

1 02 Hydrology of MaJOr Estuar~es and Sounds of North Carohna

:I -< Q.

0 0

?J s. ;. ~ )>

a= ~

3 ~ ;;-~ c :I Q.

"" ~ c ~ 5 ~

VI -< "' ;-3

.... = IN

Table 4.5. Summary of chem1cal analyses of water samples collected at key stat1ons m the Roanoke R1ver basm Chem1cal constituents are m m1lllgrams per hter, except spec1f1c conductance, pH, and color (Adapted from Wilder and Slack, 1971a)

~ ~~ Dissolved Hardness I

';0 u solids as eaco3

........ 01 I U U .. N X: ;- ::c

~ ..... "" t. g~~ ... ';' OJ~ s 0 01 >. g 0 ~ -;a ~ e ~ :z: ... "0 u~N

.... 110 ..... u ... ~ OJ "' ~ . ~ ..

~6 "' -; ~ § :z: § 01 u ..... Station name .. 0,!:; OJ ~ r: .. OJ

... ~ r: ... liON OJ "' OJ "' g~ ... u "' I

0 .. 01 ... .., ..... OJ 110 ~ a ..... ... 0 .. "0 "0 ... .t! :;)U ..... :=5 .. ~1

..... :;) a "' 01 ~ :;) "' a ., ..c ... ..... ..... 01 c. ..,. :;) ...... 0 .. !l a 0 c. ..... <:r OJ .. u .... OJ :;) ..... a C.GI .. OJ ..... r: u r: .... Cl) .. "' .. .. .. "' .... o u u r: I..C u ... 0 0

~ !l ... "' !.!: ... > ..... 0 ..... 110 ~ "' .... 0 0 ... 0 CI)CI) ..... .-<110 r: .. OJ u .t! ..... ... r: "0 <J ..... 6 ~ ..... .t! ....... "' 01 01 0 01 ""='a ::c 0 .. Cl)

.=! "' ..... .. "' ;! 0 0

"' 0 "" .... :;) :z: "" "' u u a :z: u "'"0 0 c. u

"' .... u "' "" oQ "' "" 02080500 Roanoke River at Roanoke Rapids, 8,410 ~ct 1948 daily Max 17 59 25 3 9 20 2 6 110 24 9 9 5 2 2 10 74 117 73 3 206 7 8 45

N C - through Min 6 5 00 4 9 1 6 3 1 7 23 4 0 2 0 0 1 00 46 50 19 0 60 6 4 3 Sept 196 Avg 13 06 6 6 2 6 6 0 1 4 34 6 3 3 5 1 6 02 58 64 27 0 83 7

02081000 Roanoke River near Scotland Neck, 8, 700 k>ct 1944 daily Max 16 3 3 13 5 9 17 13 131 12 19 4 5 2 10 173 78 57 1 155 7 4 80 N C through Min 6 2 00 4 8 1 2 4 5 1 4 11 1 2 1 0 0 0 00 47 44 18 0 68 6 1 5

Sept 196 Avg 11 13 8 4 2 4 9 0 3 0 45 7 9 5 7 1 1 5 02 78 63 31 0 118 19

02081094 Roanoke River at Jamesville, N C about k>ct 1954 daily Max 14 59 15 4 1 14 3 6 72 12 12 5 5 9 23 98 83 52 4 188 7 7 90 9,250 through "' Min 2 8 00 4 0 5 3 7 6 17 2 0 2 8 0 3 00 35 33 12 0 55 6 2 5

Sept 196 Avg 8 7 10 8 6 2 5 8 0 2 1 40 6 9 6 1 1 2 1 06 72 67 31 0 105 30

02081122 Cashie River at Windsor, N C 179 Oct 1961 montbly Max 23 80 11 3 1 28 4 8 60 34 23 4 1 7 50 129 115 37 32 203 6 9 160 through Min 1 5 00 2 2 5 1 6 9 5 2 6 2 0 0 3 00 49 22 10 0 34 5 3 20

Sept 196J Avg 8 3 19 5 1 1 4 8 2 2 0 20 8 2 9 1 2 9 05 77 49 18 5 82 81

____.____ ---

public water supplies, but Iron can be removed easily with treatment At all stations except Roanoke Rapids, color sometimes exceeds the upper limit of 75 color umts re­commended m the same report Downstream from Roanoke Rapids, color mcreases m the Roanoke River owmg to mflows from swampy areas, which Impart color from decaymg vegetation and the leachmg of humic acids The Cash1e River, m this regard, IS typical of streams drammg coastal swamp areas m the lower half of the Roanoke River basm, where even average color values may exceed recommended upper limits (table 4 5)

SUMMARY AND DISCUSSION

The Cape Fear River and the Northeast Cape Fear River are the only maJor North Carohna estuaries havmg relatively duect ocean connections As a result, tidal ranges there are several feet m most places and the move­ment of saltwater m and out of these estuaries IS very sen­Sitive to tides and changmg freshwater mflows However, the estuary portions of the Neuse-Trent, Tar-Pamlico, Chow an, and Roanoke R1ver systems are semi-enclosed by the Outer Banks and are subject to the t1de-dampemng effects of Pamlico and Albemarle Sounds As a result, tidal ranges there are less than 0 5 foot m most places and salimt1es change much more slowly m response to chang­mg freshwater mflow

In the Cape Fear River and Northeast Cape Fear River estuanes, short-term flow IS dommated m most lo­cations by ocean tides, followed m Importance by fresh­water mflow and wmds In Pamhco Sound, Albemarle Sound, and all other maJor estuaries, with the probable exception of the Roanoke, wmds are usually the dommant short-term current-producmg force, followed m Impor­tance by ocean tides and freshwater mflow

The average annual outflow from the 9,140 m12 area compnsmg the Cape Fear River basm Is about 11 , 100 ft3/s Pamhco Sound, havmg a surface area of about 2,060 m12

, receives direct dramage from a 12,520 m12 area (m­cludmg the area of the sound) In additiOn, 1t receives m­dJrect dramage through Croatan and Roanoke Sounds from the Albemarle Sound system (18,380 m12) The average flow from th1s 30,900 m12 area IS about 32,000 ft3/s Of this amount, about 17,300 ft3/s IS contnbuted by the Al­bemarle Sound system

Flow m the Cape Fear River Is affected by ocean tides upstream to Lock I , about 65 miles upstream from Its mouth In the Northeast Cape Fear River, tides extend to about 50 miles upstream from W1lmmgton Measure­ments m the Cape Fear R1ver estuary near Phoemx mdi­cate that reversals of flow dunng tidal cycles are the rule rather than the exceptiOn, only when the freshwater out­flow near Phoemx IS greater than about 13,000 ft3/s are upstream flows dunng flood tides prevented For the

1 04 Hydrology of MaJor Estuanes and Sounds of North Carohna

smgle senes of measurements available m the Northeast Cape Fear estuary on October 23, 1969, a freshwater out­flow of about 22,000 ft3/s at the measunng Site 6 4 miles upstream from the mouth would have been required to prevent flow reversal

Rehable measurements of tide-affected flow over tidal cycles have not been made on other maJor North Carohna estuaries, but the upstream limits of tide effects have been fauly well established Ocean tides affect the Neuse River upstream to Fort Barnwell, about 63 miles from the mouth They affect the Trent River upstream to Pollocksville, about 57 miles upstream from the mouth of the Neuse River The upstrean1 hm1t of tide effects m the Tar R1ver IS near Greenville, about 57 miles upstream from the mouth of the Pamhco R1ver In the Roanoke River, It IS thought that the upstream hmit of tide effects IS near Hamilton, about 60 miles from the mouth The Chowan River estuary IS affected by ocean tides through­out Its 50-mile length

Freshwater entenng the maJor estuaries IS generally, where not contammated, of suitable quahty for public sup­ply and most mdustnal uses In some estuaries, however, uon sometimes exceeds the 0 3 mg/L recommended upper hm1t (U S Environmental ProtectiOn Agency, 1976 [ 1977]) for drmkmg water, and highly colored water from swamp dramage may exceed the 75-color-umt recom­mended upper hm1t Algal blooms sometimes reach nui­sance proportiOns m several estuaries, particularly the Neuse, Pamhco, and Chowan Rivers, where nutnents are usually abundant

All maJor North Carohna estuaries except the Roanoke River are subject to at least occasiOnal mtrus1on of saltwater Maximum upstream advances of the saltwa­ter front (200 mg/L chlonde) occur as a result of extended penods of low freshwater mflow, or, occasiOnally, as a result of currents dnven upstream by humcane-force wmds In fact, the maximum-of-record upstream saltwater mtrus10n for most North Carohna estuaries occurred dur­mg or m the aftermath of the passage of Humcane Hazel on October 15, 1954

The maximum known upstream mtrus1on of the salt­water front m the Cape Fear River was to about 20 miles upstream from Wilmmgton, m the Northeast Cape Fear River, to about 23 miles upstream from Wilmmgton, m the Neuse River, to about 2 2 miles northeast of Fort Barnwell, m the Trent R1ver, to about 4 5 miles upstream from Pollocksville, m the Tar River, to about 20 miles up­stream from the mouth, and m the Chowan R1ver, to near Eure All these mtrus10ns were associated with humcane conditions, except those of the Neuse and Chowan Rivers, which were caused by nonhumcane low-flow conditions

Data on shoaling rates and sediment transport from upstream sources for the Cape Fear and Northeast Cape Fear Rivers show that upstream sources can account for only a small proportiOn of new shoahng matenals found

m the lower channelized reaches Most shoahng matenal must be denved from slumpmg along channels, from nearby shore eroston, from old spotl areas, or posstbly from ocean sedtments earned upstream by near-bottom de­nstty currents Not enough data ts available from other es­tuartes dtscussed m thts report to determme whether or not thts concluston holds true elsewhere

It ts appropnate here at the end of the report to ob­serve that there are sttll a number of defictenctes m our knowledge of even the baste hydrology of North Carolina's estuartes and sounds and that some of the more complex phystcal, chemtcal, and phys10logtcal processes at work m them are far from bemg adequately understood or defined Among the deftctenctes m baste knowledge are ( 1) lack of measurements of tide-affected flow and cir­culatiOn patterns m most estuanes, (2) a general lack of know ledge of movement and dtspersion charactensttcs of contammants whtch may be acctdentally spilled mto the estuartes, (3) a lack of chemical analyses other than sahn­Ity for waters m the central area of Pamhco Sound and m many small, but tmportant, estuanes servmg as fish nurse­nes, and (4) a lack of rehable models to predict sahmty advances under vanous condtttons of freshwater mflow and ttdes Among deftctencies m understandmg of the more complex hydrologic phenomena are ( 1) lack of knowledge of the fate of nutnents and pesttctdes m runoff from agncultural runoff whtch enters the estuartes and sounds, (2) a lack of knowledge of the sources and methods of transport and deposition of sedtment m many estuartes, (3) madequate knowledge of hydrologic condi­tiOns whtch may contnbute to (or prevent) destructtve algal blooms, (4) poor defimtton of runoff from canals drammg agncultural areas along the coast, and of the ef­fects of changed runoff patterns m those areas on fishery resources, (5) madequate understandmg of the posstble maJor role of bottom sedtments m actmg as a trap for nu­tnents, pesttctdes, and trace metals entenng the estuanes and sounds, (6) lack of detatled knowledge of the effects of wmds on water levels, ctrculatton, and mixmg m es­tuanes and sounds, and (7) lack of knowledge of the ef­fects of operatiOn of upstream reservmrs on phystcal, chemical, and btologtcal processes m the downstream es­tuanes and sounds

SELECTED REFERENCES

Amem, Mtchael, and Atran, D S , 1976, Mathematical modeling of ctrculatiOn and humcane surge m Pamlico Sound, North Carolina Umverstty of North Carolina Sea Grant pubhcatton no 76-12, 102p

Batley,R S ,andHaven,D S ,March 1963,Mtlfml,afnllyweed that rums your sport Vtrgtma Wtldlife, 3 p

Bames, W D , 1957, Ttdal currents m constncted mlets Proceed­mg~ of Conference on Coastal Engmeenng, p 545-561

Bames, W D , and Knapp, D J , 1965, Wmd dnven water cur­rents Journal of the Hydraulics DIVISIOn, Amencan Soctety ofCivtl Engmeers, v 91, no HY2, p 205-221

Bowden, K F , 1967, CirculatiOn and diffusiOn, m Estuanes Amencan Assoctatwn for the Advancement of Sctence publi­catiOn no 83, Washmgton D C , 757 p

Bowden, W B , and Hobbte, J E , 1977, Nutnents m Albemarle Sound, North Carohna Untversity of North Carohna Sea Grant publication 75-25, 187 p

Bretschneider, C L , 1966, Engmeenng aspects of humcane surge, 1n Ippen, A T , ed , Estuary and coastline hydro­dynamics McGraw Hill, p 231-256

Broome, T G , 1968, An analysts of flow m ttdal mlets unpub­lished Master of Science thests, Department of Ctvil Engmeer­mg, North Carolina State Umversity, Raletgh, N C

Brown, E I , 1928, Inlets on sandy coasts Proceedmgs, Amencan Soctety ofCtvtl Engmeers, v 54, pt 1, p 505-553

Carpenter, E J , 1971, Effects of phosphorous mmmg wastes on the growth of phytoplankton m the Pamlico River estuary Chesapeake Science, v 12, p 85-94

Colquhoun, 1966, Geomorphology of nver valleys m the southeast­em Atlantic Coastal Plams Southeastern Geology v 7, no 3, p 101-109

Damel, C C , Ill, 1977, Dtgital flow model of the Chowan River estuary, North Carolina U S Geological Survey Water Re­sources I nvestlgatwns 77-63, 84 p

Davts, G J , Bnnson, M M , and Burke, W A , 1978, Orgamc carbon and deoxygenatiOn m the Pamhco Rtver estuary Um­verstty of North Carohna Water Resources Research Institute report no 78-131 , 123 p

Dewtest, R J M , 1970, Hydrology of the Pamlico Estuary m the State of North Carolma, 1n Symposmm on the Hydrology of Deltas, v 2, InternatiOnal Assoctatton of Scientific Hydro­logy, Umted NatiOns Educational, Sctentific, and Cultural Or­gamzatton pubhcatwn 91, p 375-385

Dronkers, J J , and Schofield, J C , 1955, Ttdal computatiOns m shallow water Proceedmgs, Amencan Society of Ctvil En­gmeers, 81 (714), p 29-31

Folger, David W , 1972, Charactensttcs of estuanne sediments of the Umted States U S Geologtcal Survey ProfessiOnal Paper 742,94p

Forch, C , Knudsen, Martm, and Sorenson, S P L , 1902, Be­nchte Uber dte Konstantenbestlmmungen zur Aufstellung der hydrographtschen Tabellen, D Kgl Danske Vtdensk Selsk Sknfter, 6 Raekke, Naturvidensk OG Mathern, Afd XII 1, 151 p

Frankenberg, Dtrk, 1975, Salt marshes, m Proceedmgs of a sym­posmm on coastal development and areas of environmental concern, at Greenvtlle, North Carolina, March 5, 1975 Um­verstty of North Carohna Sea Grant publication 75-18, 90 p

Gtese, G L , and Barr, J W , 1967, The Hudson River Estuary-a prelimmary mvesttgatwn of flow and water quahty character­tsttcs New York Water Resources Commtssion Bulletm 61, 37p

Hardy, A U , and Carney, C B , 1962, North Carolina humcanes U S Weather Bureau, Raleigh, N C , 26 p

Hathaway, J C , 1971, Data file, Contmental Margm Program, At­lanttc Coast of the Umted States, v 2, Sample collectiOn and analyttcal data Woods Hole Oceanographic Instttute Refer­ence 75-15,496 p

Selected References 1 OS

Hayes, M 0 , and Kana, T W , 1976, Temgenous clastic deposi­tiOnal environments-some modern examples Coastal Re­search Division, Department of Geology, Umverstty of South Carolina

Heath, R C, 1975, Hydrology of the Albemarle-Pamlico regiOn, North Carolina-a prelimmary report on the Impact of agncul­tural developments U S Geological Survey Water Resources Investigations 9-75,98 p

Ho, F P , and Tracey, R J , 1975a, Storm tide frequency analysts for the coast of North Carolina, south of Cape Lookout Na­tional Oceamc and Atmosphenc AdministratiOn Techmcal Memorandum NWS HYDR0-21, 44 p

--1975b, Storm tide frequency analysts for the coast of North Carolina, north of Cape Lookout NatiOnal Oceamc and At­mosphenc AdmtmstratiOn Techmcal Memorandum NWS HYDR0-27, 46 p

Hobbie, J E , 1974, Nutnents and eutrophicatiOn In the Pamlico Rtver estuary, N C , 1971-73 Water Resources Research In­stitute report no 74-100, 239 p

--1975, Nutnents In the Neuse Rtverestuary, North Carolina Umverstty of North Carolina Sea Grant publicatiOn no 75-21, 183p

Horton, D B , Kuenzler, E J, and Woods, W J , 1967, Current studies In Pamlico Rtver and estuary of North Carolina Um­verstty of North Carolina Water Resources Research Institute report no 6, 21 p

Hubbard, E F , and Stamper, W G , 1972, Movement and disper­Sion of soluble pollutants In the Northeast Cape Fear Rtver es­tuary, North Carolina U S Geological Survey Water-Supply Paper1873-B,p El-E31

Ippen, A T (ed ) 1966, Estuary and coastline hydrodynamics McGraw Htll, New York, 744 p

Jackson, N M , Jr, 1967, Flow of the Chowan Rtver, North Carolina, a study of the hydrology of an estuary affected pnmanly by winds U S Geological Survey open-file report, 29p

Jacobsen, J P , and Knudsen, M , 1940, Urnormal 1937 or pn­mary standard seawater 1937 Umon Geod et Geophys In­tern , Assn d'Oceanographtc, Pub sci no 7, Liverpool, 38 p

Jarrett, T J , 1966, A study of the hydrology and hydraulics of the Pamlico Sound and their relations to the concentratiOn of sub­stances In the sound unpublished Master of Sctence thesis, Department of Ctvtl Engineenng, North Carolina State Um­verstty at Raletgh, N C , 156 p

Johnson, D W , 1938, Shore processes and shoreline develop­ment New York, John Wtley, 1919 [repnnted 1938]

Keefe, D W , 1972, Marsh production-a summary of the litera­ture ContributiOns In Manne Science 16 163-179

Keulegan, G H , 1967, Ttdal flow In entrances-water level fluctua­tions In basins In commumcat10n with seas Techmcal Bulletin no 14, Committee on Ttdal Hydraulics, US Army Corps of Engineers, VIcksburg, Mtss

Keulegan, G H , and Hall, J V , 1950, A formula for the calcula­tiOn of the tidal discharge through an Inlet U S Beach ErosiOn Board Bulletin, v 4, no I, p 15-29

Knowles, C E , 1975, Flow dynamics of the Neuse Rtver, North Carolina Umverstty of North Carolina Sea Grant publicatiOn 75-16, 18 p [and appendices]

1 06 Hydrology of MaJor Estuar1es and Sounds of North Carohna

Kneger,R A ,Hatchett,J L ,andPoole,J L, 1957,Prehminary survey of sahne-water resources of the Umted States U S Geological Survey Water-Supply Paper 1374, 172 p

McHugh, J L , 1966, Management of estuarine fishenes, m Sym­postum on Estuanne Ftshenes Amencan Ftshenes

Magnuson, N C , 1967, Hydrologic tmphcat10ns of a deepwater channel In Pamhco Sound, m Proceedings, Symposmm on Hy­drology of the Coastal Waters of North Carohna, at North Carolina State Umverstty, Raletgh, N C , May 12, 1967 Um­verstty of North Carolina Water Resources Research Institute report no 5, p 130-141

Marshall, N , 1951, Hydrography of North Carolina manne waters, m H F Taylor and Associates, Survey of manne fishes of North Carolina Chapel Htll, N C , Umverstty of North Carolina Press, 555 p

NatiOnal Academy of Sciences, NatiOnal Academy of Engineenng, 1972 [1974], Water quahty cntena 1972 US Government Pnnting Office, 594 p

National Ocean Survey, Ttdal current tables-Atlantic coast of North Amenca US Department of Commerce, NatiOnal Oceamc and Atmosphenc AdmtmstratiOn, Issued annually

NatiOnal Ocean Survey, Ttde tables-htgh and low water predic­tions-east coast of North and South Amenca U S Depart­ment of Commerce, NatiOnal Oceamc and Atmosphenc Ad­ministratiOn, Issued annually

National Techmcal Advtsory Committee to the Secretary of the In­tenor, 1968, Water quality cntena U S Government Pnnting Office, Washington, D C

North Carolina Council of Civil Defense, 1955, North Carohna humcane proJect Raleigh, N C , 64 p

North Carohna Office of Water and Air Resources, 1972 North Carohna water plan progress report (ch 27), Cape Fear River basin, v I North Carolina Department of Natural and Economic Resources, Raleigh, N C , 323 p

Odum, E P, 1959, Fundamentalsofecology Philadelphia, W B Saunders

Pels, R J , 1967, Sediments of Albemarle Sound, North Carohna unpubhshed Master of Science thesis, Umversity of North Carolina at Chapel Hill, N C , 73 p

Ptckett, T E , 1965, The modern sediments of Pamhco Sound, North Carohna Southeastern Geology, v II, p 53-83

Pntchard, D W , and Carter, H H , 1971, Estuanne Circulation patterns, m The estuarme environment-estuanes and estuanne sedimentatiOn lecture notes for Amencan Geologtcal Institute Short Course "The Estuanne Environment," held at Wye Insti­tute, Cheston-on-Wye, Md , October 30-31, 1971, 339 p

Riley, C D , 1972, Waste disposal and water quahty m the es­tuanes of North Carohna North Carolina State Umversity School ofEngmeenng, Raleigh, N C , 68 p

Roelofs, E W , and Bumpus, D F , 1953, The hydrography of Pamhco Sound, m Bulletin of Manne Science of the Gulf and Canbbean,v 3,no 3,p 181-205

Schubel, J R , 1971 , Estuanne ctrculation and sedtmentation, m The estuarme envtronment-estuanes and estuanne sedimenta­tiOn lecture notes for Amencan Geological Institute Short Course "The Estuanne Environment," held at Wye Institute, Cheston-on-Wye, Md , October 30-31, 1971, 339 p

Schureman, P , 1924, A manual of the harmomc analyses and pre­diction of tides U S Coast and Geodetic Survey Special Pub­licatiOn 98,416 p

Schwartz, F W , and Chestnut, A F , 1972, Hydrographic atlas of North Carohna estuanne and sound waters, 1972 Umver­stty of North Carohna Sea Grant publicatiOn 73-12, 132 p

Stmmons, C E , 1976, Sedtment charactensttcs of streams m the eastern Ptedmont and western Coastal Plam regtons of North Carohna, U S Geologtcal Survey Water-Supply Paper 1798-0,32p

Smger,J J ,andKnowles,C E, 1975,Hydrologyandctrculation patterns m the vtcmtty of Oregon Inlet and Roanoke Island, North Carohna Umverstty of North Carohna Sea Grant pubh­catiOn75-15, 171 p

Stanley, D W , and Hobbte, J E , 1977, Nttrogen recychng m the Chowan Rtver Water Resources Research Instttute report no 121' 127 p

Sverdrup, H U , Johnson, M W , and Flemmg, R H , 1942, The oceans-thetr phystcs, chemistry, and general biOlogy En­glewood Chffs, N J , Prenuce Hall, 1087 p

Thayer, G W , 1975, The estuary-an area of environmental con­cern, m Proceedmgs of a symposmm on Coastal development and areas of environmental concern, Greenvtlle, N C , March 5, 1975 Umverstty of North Carohna Sea Grant pubhcat10n 75-18, 90p

Tthansky, D P , and Meade, N F , 1974, Esttmatmg the economtc value of estuanes to U S commerctal fishenes Prepnnt of Chapter m the Nattonal Estuary Study, 47 p

U S Army Corps of Engmeers, 1961, Report on the Troptcal Hur­ncane of September (Donna) W tlmmgton, N C

--1976, A feastbthty study on reducmg mamtenance dredgmg costs at the Mthtary Ocean Termmal, Sunny Pomt Wtl­mmgton, N C , 133 p

US Congress, 1935, Beach eros10n at Kttty Hawk, Nags Head, and Oregon Inlet, North Carohna 74th Congress, I st Sesston, H R 155

US Envuonmental Protection Agency, 1975, NatiOnal mtenm pnmary dnnkmg water regulations Federal Regtster, v 40, no 248,p 59566-88

--1976 [ 1977], Quahty cntena for water U S Government Pnntmg Office, 256 p

U S Geologtcal Survey, Water resources data for North Carolma

U S Geologtcal Survey water-data report senes, 1ssued annu­ally

Wtlder, H B, 1967, Hydrology of sounds and estuanes m North Carohna, m Proceedmgs of a symposmm on hydrology of the coastal waters of North Carohna, at North Carohna State Um­verstty, Raletgh, N C , May 12, 1967 Umverstty of North Carohna Water Resources Research Institute report no 5, p 115-129

Wtlder, H B , and Hubbard, E F , 1968, Intenm report on seawa­ter encroachment m the Cape Fear estuary, North Carohna U S Geologtcal Survey open-file report, 36 p

Wtlder, H B , Robtson, T M , and Lmdskov, K L, 1978, Water resources of northeast North Carohna U S Geologtcal Sur­vey Water Resources InvestigatiOns 77-81 , 113 p

Wtlder H B , and Slack, L J , 1971 a, Summary of data on chemi­cal quahty of streams of North Carohna, 1943-67 U S Geologtcal Survey Water-Supply Paper 1895-B, 236 p

--1971b, Chemtcal quahty of water m streams of North Carohna U S Geologtcal Survey Hydrologtc Invesugattons Atlas HA-439, 2 sheets

Wtlhams, A B , Posner, G S , Woods, W J , and Deubler, E E , Jr , 1967, A hydrographic atlas of larger North Carolina sounds U S Ftsh and Wtldhfe Servtce, Data Report no 20, 130p

Wtlson, K A , 1962, North Carohna wetlands-thetr d1stnbut10n and management North Carohna Wtldhfe Resources Com­mtsston, Raletgh, N C , 169 p

Wmner, M D, Jr, and Stmmons, C E, 1977, Hydrology of the Creepmg Swamp watershed, North Carohna, wtth reference to potential effects of stream channelizatiOn U S Geologtcal Survey Water Resources Investtgattons 77-26, 54 p

W mslow, Francts, 1889, Report on the sounds and estuanes of North Carohna wtth reference to oyster culture U S Coast and Geodetic Survey Bulletm no 10, p 52-136

Woods, W J , 1967, Hydrographic studtes m Pamhco Sound, m Proceedmgs of a symposiUm on hydrology of the coastal wat­ers of North Carohna, at North Carolma State Umverslty, Raletgh, N C , May 12, 1967 Umverstty of North Carohna Water Resources Research Instttute Report no 5, p 104-114

Selected References 1 07

METRIC CONVERSION FACTORS

The following factors may be used to convert the U.S. customary units published in this report to the International System of Units (SI).

Multiply U.S. customary unit By

inches (in) feet (ft) miles (mi)

square feet (ft 2 )

square miles (mi 2 )

acre

cub~c yards (yd 3 )

acre-feet

cubic feet per second (ft 3 /s)

cubic feet per second per square mile [(ft 3 /s)/mi2 ]

feet per second (ft/s) miles per hour (mi/hr)

pounds (lb avoirdupois) ton (short, 2,000 lbs)

Length

25.4 .3048

1.609

Area

.0929 2.590

4,047

Volume

.764 1,233

Flow

.02832

.01093

Velocity

.3048 1.609

Mass

.4536

.9072

To obtain SI (metric) unit

mill~meters (rnm) meters (m) kilometers (km)

square meters (m2 )

square kilometers (km2 )

square meter~ (m2 )

cubic meters (m 3 )

cubic meters (m 3 )

cubic meters per second (m3 /s)

cubic meters per second per square kilometer [(m~/s)/km2 ]

meters per second (m/s) kilometers per hour (km/hr)

kilograms (kg) tonne (t)

Nat~onal Geodet~c Vert~cal Datum of 1929 (NGVD of 1929): A geodetic datum derived from a general adjustment of the f~rst-order level nets of both the Un~ted States and Canada; formerly called mean sea level. NGVD of 1929 is referred to as sea level in the text of this paper.

*U S GOVERNMENT PRINTING OFFICE 1985-461-431 20001

1 08 Hydrology of MaJor Estuar1es and Sounds of North Carohna