1. Puget Sound Coastal Geomorphology
Background materials for NearPRISM discussion of Puget Sound shoreline geomorphology
September 11, 2000
Hugh Shipman
WA Dept of Ecology

2. Questions
How is nearshore biology impacted by changes in sediment supply associated with a large landslide or with shoreline armoring?
How do geomorphological processes affect landscape-scale ecological processes (e.g. migratory pathways, eelgrass patchiness)?
Are there predictable relationships between geomorphological process, beach substrate, and biological community?

3. Puget Sound 2000 miles of shoreline Narrow, steep nearshore zone
Significant lateral heterogeneity
Geology and geomorphology
Wave exposure and tidal conditions
Hydrology (rivers, streams, groundwater)
Nearshore ecology linked to shoreline geomorphological process

4. Nearshore Def: Top of bluff to limit of photic zone
Distinct geomorphological regimes - river deltas, barrier beaches, rocky shores, and open bluff-backed coast
Wave action determined by local wind field and shoreline shape/bathymetry
Dominance of longshore sediment movement
Mixed gravel and sand beaches
Complex beach hydrology (e.g. seeps)

5. Puget Sound Shoreline

6. Sediment transport Sources Longshore Transport Sediment sinks
Bluff erosion vs. Fluvial
Highly variable, often coarse sediment
Longshore Transport
Low transport rates, particle size dependence
Major factor in geomorphological variability
Sediment sinks
Spits, lagoons and flats, deep water
Littoral cells

7. Keuler, 1988

8. Shoreline modification issues
Armoring
Nourishment
Docks and piers
Riparian changes
Shoreline Guidelines
Endangered Species Act

9. Shoreline Armoring Loss of littoral sediment Wave reflection/scour
Hydrological impacts
Loss of riparian vegetation
Passive erosion
Cumulative impact

10. Modified
shoreline
[DNR, 1998]

11. Ecology = f ( Physical Processes)
Topography
elevation, slope
Sediment structure
substrate, particle size
Sediment dynamics
turnover, disturbance
Hydrology
estuaries, seepage
Geochemistry

12. Beach Models Longshore sediment movement Beach sediment dynamics
Long-term changes to the nearshore tied to changes in longshore sediment supply
Beach sediment dynamics
Short-term changes in beach state related to waves and tides

13. Sediment Budget model
Address beach processes over 100s-1000s meters and over years to centuries (Large Scale Coastal Behavior)
Important for evaluating questions relevant to coastal managers
Useful for addressing landscape-scale ecological questions (e.g. habitat distribution)
Model “currency” is sediment - possibly reflecting behavior of different particle sizes
Model cells might be segments of shoreline

14. UPLAND NEARSHORE OFFSHORE Bluff erosion Streams Dunes and backshore
Shoreline armoring, hydrologic modifications
UPLAND
Bluff erosion
Streams
Dunes and backshore
Rivers
NEARSHORE
Upper Beach
Longshore Transport
Longshore Transport
Lower Beach
Groins, jetties
Tide Flats
Small estuaries
Deep Water
OFFSHORE

15. Beach Dynamics model
Address changes in beach sediment at a scale of centimeters to meters, and over time periods of hours, storms, or seasons.
Important to understanding relationship between sediment, biological, and chemical processes.
Links to other PRISM modules (oceans, nutrients)
Model “currency” is chemical constituent (e.g. carbon)
Model cell is a unit area (1-10 meters square?)

16. Information Sources
Limited literature on estuarine and mixed gravel/sand beaches
Little observational data on Puget Sound
Limited knowledge of geomorphological-biological interactions outside of large river deltas