robert bourke, natalie waters, and jordon moniuszko water ...proposal to test flow restoration by...

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Robert Bourke, Natalie Waters, and Jordon MoniuszkoWater Resource Sustainability Issues on Tropical Islands

December, 2015

Estuary Rehabilitation

Stream Flow Restoration to

Kaelepulu Estuary

Kailua Bay

1,000 BC1 Km

Kawai Nui Swamp

KaelepuluPond

Kailua Bay

19281 Km

Kawai Nui Swamp

KaelepuluPond

Kailua Bay

KaelepuluPond

Kawai Nui Swamp

1928

19521 KmNew

Channel

1952

19661 Km

1952

1966

19521966

1990

1958

ESTUARY CHALLENGES

• EXCISED FROM HEADWATER FLOWS

• DECREASED STREAM MOUTH EXCHANGE

• BATHYMETRY CHANGES

• URBAN STORM WATER FLOWS

• INVASIVE SPECIES

ESTUARY CHALLENGES

• EXCISED FROM HEADWATER FLOWS

• DECREASED STREAM MOUTH EXCHANGE

• BATHYMETRY CHANGES

• URBAN STORM WATER FLOWS

• INVASIVE SPECIES

ESTUARY IS ONLY EXPOSED TO TIDAL FLOW ON A PERIODIC BASIS

MANUAL OPENING OF STREAM MOUTH ON ~MONTHLY SCHEDULE BY C&C HONOLULU

Total Tidal Inflow 0.23 M cuft

Total Tidal Inflow 21x103m3

Total Tidal Inflow 0.23 M cu ft

Total Tidal Inflow 0.75 M cu ft

Timing of Stream Mouth Opening to Maximize Initial Outflow Results in an Increase of Total Exchange

ESTUARY CHALLENGES

• EXCISED FROM HEADWATER FLOWS

• DECREASED STREAM MOUTH EXCHANGE

• BATHYMETRY CHANGES

• URBAN STORM WATER FLOWS

• INVASIVE SPECIES

SHOALING OF STREAM CHANNEL AT POND OUTFLOW INHIBITS TIDAL FLOW OF SALT WATER TO THE POND

ESTUARY CHALLENGES

• EXCISED FROM HEADWATER FLOWS

• DECREASED STREAM MOUTH EXCHANGE

• BATHYMETRY CHANGES

• URBAN STORM WATER FLOWS

• INVASIVE SPECIES

Being addressed throughState TMDL City NPDES

ESTUARY CHALLENGES

• EXCISED FROM HEADWATER FLOWS

• DECREASED STREAM MOUTH EXCHANGE

• BATHYMETRY CHANGES

• URBAN STORM WATER FLOWS

• INVASIVE SPECIES

A 2004 ELRA $24K – 319 GrantB 2009 KCC $29K – Hi. Comn. Foundation

& Castle FoundationC 2016 (?) C&C $750K State funded

A

B

C

Of the principle problems confronting the estuary:

• Pollutant flows from urban storm drains• Poor salt wedge penetration into pond • Poor exchange at stream mouth• Invasive Species (mangrove)• Lack of sufficient water flow

Improving water flow was deemed likely to provide the greatest benefit with the least effort.

2.0

1.0

22.5

1.0

NOTE: All volumes given in millions of cubic feet

Estuary Area – 526,300m2 135 acres

Volume – 750,000m3 = 26.5 Mft3

Volume of 8-inch (0.2m) tidal inflow – 106,000m3 = 3.7 Mft3

CLASSICAL SALT WEDGE AND EXCHANGE CURRENTS IN AN ESTUARY

Lanikai Bridge (Kbay Tide) Water Height Ft. MLLW

0

1

2

3

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Feet

MLLW

Lanikai Bridge Water Turbidity

01020304050

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Turb

idity

NTU

Lanikai Bridge Water Salinity

01020304050

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Salin

ity P

PT

Kaelepulu Rain per Hr

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Days, Beginning Dec. 18, 2010

Rain

Inch

/Hr.

A B C D

DEPTH

TURBIDITY

SALINITY

RAIN

6 M cu ft

PHYSICAL WATER QUALITY TRANSECTS OF ESTUARY

CONDUCTED BEFORE AND AFTER EACH STREAM MOUTH OPENING EVENT

T, Salinity, pH, NTU, Chl-a, PC, DO%

@ 15 cm30 cm60 cm 120 cm180 cm

Beach PondChannel

Beach PondChannel

Shallows

9/15/13 Salinity Kawainui Pre Opening

9/15/13 Salinity Kaelepulu

9/26/13 Salinity Kawainui Post opening

9/26/13 Salinity Kaelepulu

11/16/13 Salinity Kawainui – Pre opening

11/16/13 Salinity Kaelepulu

9/15/13 Oxygen Kawainui Pre Opening

9/15/13 Oxygen Kaelepulu

9/26/13 Oxygen Kawainui Post opening

9/26/13 Oxygen Kaelepulu

11/16/13 Dissolved Oxygen Kawainui – Pre opening

11/16/13 Dissolved Oxygen Kaelepulu

Salinity for 10 Sampling

Events

Other Parameters Tracked:• Temperature• Dissolved Oxygen• pH• Turbidity• PC• CHL-A• Volume Exchange

% Exchange = (SF-SI) / (35-SI)

% Exchange = (SF-SI) / (35-SI)

PROPOSAL TO TEST FLOW RESTORATION BY INSTALING TEMPORARY SIPHON OVER LEVEE

~ 6 L/s

2 ft3/sec 5.2 M ft3/Month ~1 ft Rise (- Evaporation)

2 ft3/sec 5.2 M ft3/Month 0.9 ft Rise (- Evaporation)

Construction of Four 6-inch PVC

Siphons over Levee

TEST TRIAL IS HYPOTHESIZED TO DEMONSTRATE THAT THE FLOW

RESTORATION WILL

• Increase monthly water exchange in the KawainuiStream Channel thereby improving water quality

• Increase volume and period of exchange with the ocean by enhanced opening head and flow dynamics

Experiment DurationControl Portion of Experiment

Marsh Water Surface Rate of Fall = 0.20 inch/da Marsh Water Surface Rate of Fall = 0.2 to 0.34 inch/da

WATER SURFACE ELEVATION OF KAWAINUI MARSH SOURCE WATER

WATER SURFACE ELEVATION OF KAWAINUI STREAM SHOWING STREAM MOUTH

OPENING PERIODS

0.5

1

1.5

2

2.5

3

J F M A M J J A S O

Wat

er S

urfa

ce E

leva

tion,

Feet

MLL

W

Months, 2015

Kaelepulu Water Surface Elevation, 2015 Feet MLLW

Syphons ON

WATER SURFACE ELEVATION OF KAWAINUI STREAM WAS ABOVE FLOOD THREAT LEVEL

ON THREE OCCASIONS

0.5

1

1.5

2

2.5

3

J F M A M J J A S O

Wat

er S

urfa

ce E

leva

tion,

Feet

MLL

W

Months, 2015

Kaelepulu Water Surface Elevation, 2015 Feet MLLW

Periods of Increased Flood Threat due to High Water Surface Elevation

Stream Mouth Openings

Syphons ON

WATER SURFACE ELEVATION OF KAWAINUI MARSH SOURCE WATER

WATER SURFACE ELEVATION OF KAWAINUI MARSH SOURCE WATER

~ 3M cu ft Water Transferred Each Month

3M cu ft

FRESH WATER INFLOW SPREADS RAPIDLY ALONG THE SURFACE OF KAWAINUI STREAM AND DOWNSTREAM TOWARDS THE BEACH.

VERTICAL MIXING OCCURS MORE SLOWLY MAINTAINING STRATIFICATION THROUGHOUT THE MONTH.

FRESH WATER INFLOW APPEARS TO FLOW RAPIDLY ALONG THE SURFACE AND EITHER EVAPORATE OR SLOWLY MIX WITH LOWER WATER LAYERS AND MAINTAINING STRATIFICATION

SYPHON INFLOW RESULTED IN GREATER STRATIFICATION OF THE ENTIRE STREAM

DISSOLVED OXYGEN REMAINED WELL BELOW 20% SATURATIONIN THE KAWAINUI STREAM THROUGHOUT THE PERIOD OF INFLOW.

D.O. WAS NOT DISTINGUISHABLE FROM CONTROL (NO SYPHON FLOW) CONDITIONS

ABUNDANT MANGROVE ALONG THIS STREAM REACH ARE LIKELY RESPONSIBLE FOR THE LOW D.O.

MANGROVE STANDS LINE THE CHANNEL WHERE DISSOLVED OXYGEN LEVELS ARE LOW

ABUNDANT MANGROVE ALONG THIS STREAM REACH ARE LIKELY RESPONSIBLE FOR THE LOW D.O.

31

Drain

KawainuiMarsh

Kawainui

High Tide 2.0 ftLow Tide 0.0 ft

Overflow Weir 2.0 ft

Oneawa CanalKawainui Stream

12” Pipe through Levee

Level Control

Drain pipe through levee from Kawainui Marsh to Kawainui StreamLevel Control Drain pipe

through levee from KawainuiStream to Oneawa Canal

QUESTIONS ?

TRACE-CONTAMINANT STUDY BY USGS

41 SAMPLE SITES WITHIN ESTUARY

71 POLLUTANT TRACERS

CAFFEINE FOUND AT 3 SITES

TRACE-CONTAMINANT STUDY BY USGS

41 SAMPLE SITES WITHIN ESTUARY

71 POLLUTANT TRACERS

CAFFEINE FOUND AT 3 SITES

TRACE-CONTAMINANT STUDY BY USGS

41 SAMPLE SITES WITHIN ESTUARY

71 POLLUTANT TRACERS

CAFFEINE FOUND AT 3 SITES