1

ESCI 321 announcements

• Problem set 2 due tonight at midnight

• Exam 2 in one week

• We will have a major review session next

Thursday. Come with questions.

• Study guide posted. Bring to class on Thursday

Ediz Hook, Port Angeles

http://www.nps.gov/olym/naturescience/damremovalblog.htm

Coasts, beaches and estuaries

I. Coast formation

II. Beaches: Rivers of sand

III. Estuaries

2

Processes determining coastal morphology and formation

Plate tectonics

Sea level changes (eustatic and relative sea level change)

Glaciers

Weathering

Wave action and storms

General scheme of coastline development (primary → secondary)

Maine N.C.

Beach morphology

Seasonal changes in beach morphology

How do waves affect beaches? (Beach movie)

Longshore sediment transport

3

Tombolo on the shore of Lake Erie, Erie, Pennsylvania

Formation of rip currents and beach cusps

Swash on beach cusps at Propriano, Corsica.

(Photo: Sogreah, France) Rip currents on a New Zealand beach

Sediment composing barrier Islands along the east coast of the U.S. is

continuously eroding and depositing toward the continent and toward the south.

4

Dune Ridge Beach Open Ocean

Lagoon Marsh Flat

Lagoonal Peat

Puget Sound coastlines

Common types of

shorelines in Puget Sound

•Sand and gravel

•Sandy beach/dunes

•Sediment-starved beach

•Mudflats

•Deltas

•Beach w/ bulkheads

Natural shoreline with development

5

Shoreline with bulkhead

Effects of beach armoring on amphipod habitat, Paihia, New Zealand

Forage fish spawning grounds in

Bellingham Bay

• Surf smelt spawn in

upper intertidal zone

• In Bellingham Bay,

they spawn only in a

few spots

• All other shorelines in

the bay have

bulkheads or seawalls

Surf smelt and sand lance spawning areas in Bellingham Bay

6

Estuaries

Estuary definitions:

(Pritchard 1952) A semi-enclosed coastal body of water that has a

free connection with the open sea and within which sea water is

measurably diluted with fresh water derived from land drainage.

(Fairbridge 1980) an inlet of the sea reaching into a river valley as

far as the upper limit of tidal rise.

Importance:

Productivity, habitat, nursery grounds, pollutant filters,

great flat spaces for development

Estuarine circulation is determined by the relative importance

of freshwater input (causing stratification) and tidal mixing

Salt-wedge estuary:

High freshwater flow rate

Well-mixed estuary:

High rate of tidal mixing

Partially-mixed estuary:

Intermediate conditions

Fjord with sill:

inhibits inflow

Two types of pressure gradients

• Barotropic (sea surface slope)

• Baroclinic (density variation, sloping isopycnals)

• Components of flow in estuaries

Pressure gradient terms

• Barotropic fieldsIsobars and isopyncnals parallel

• Baroclinic fieldsIsobars and isopyncnals inclined

Sea surface

Isobar

Isopycnal

Level surface

7

Estuarine circulation with sills

Thompson 1994

Tide

Out

In

Effect of coriolis (SJF cross section)Northern shore Southern shore

Rossby radius: velocity/Coriolis, or u/2Ωsin(φ) ≈ (0.2 m/s) / ((2*10-5 s-1) ≈ 10 km

Calculating rates of estuarine mixing,

flushing time and residence time

RSS

ST

Oi

iO

RTT iO

O

surf

T

VFT

i

deep

T

VRT

Surface water Bottom water

Circulation in Puget Sound

• Puget Sound divided into basins by sills

• Sills increase mixing and reduce mean

circulation rates & exchange among basins

8

Modeled currents in southern PS

DOE SPS model

Links to other model output

• http://faculty.washington.edu/pmacc/MoSS

ea/movies/SSS_daily_salish.mov

• http://faculty.washington.edu/pmacc/MoSS

ea/movies/SSS_hourly_salish.mov

• http://pugetsound.pnnl.gov/

PS basin circulation

Strickland 1983

“Two-layer” system: What are the

layer depths?

9

Depth of no motion

Possession Sound: 25m

Main Basin: 80m

Whidbey Basin

Admiralty inlet

Main Basin

Hood Canal

South Sound

Basins of Puget Sound

Estuarine circulation summary

• Circulation determined by balance of tides and river inflow

• Instantaneous velocities: Due to tides (barotropic P)

• Average (residual) velocities: Due to river flow.

Outflow – Barotropic pressure gradient.

Inflow – Baroclinic pressure gradient.

• Average circulation can be calculated from data on river

flow and salinity.

• Sills separate basins of Puget Sound, increasing residence

time within each basin

Next project

• Nitrogen budget for Bellingham Bay

• Due November 28th

• Assignment posted on canvas site