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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
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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
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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
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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
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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?
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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