Puget Sound Shorelines. Announcements

Transcription

1 Announcements Puget Sound Shorelines Wednesday discussion of Bates paper Bham Bay project: Updates, finals week schedules Last portion of the class: Environmental issues in Puget Sound Puget Sound shorelines: Effects of beach armoring 1

2 Factors contributing to sediment transport and erosion Waves Sediment sources As wave velocity slows with decreasing water depth, waves bend, or refract when traveling over complex bottoms Wave energy is highest at headlands Lowest in bays Quantifying wave characteristics Adding wave velocity to momentum equations Momentum equations: Force/vol Pressure Coriolis Gravity Friction Dρu/Dt = - p/ x + ρ2ωvsin(φ) + K x ( 2 ρu/ x ρu/ y ρu/ z 2 ) Dρv/Dt = - p/ y - ρ2ωusin(φ) + K y ( 2 ρv/ x ρv/ y ρv/ z 2 ) Dρw/Ddt = - p/ z - ρg + K z ( 2 ρw/ x ρw/ y ρw/ z 2 ) where Dρu/Dt = ρu/ t + u ρu/ x + v ρu/ y + w ρu/ z Dρv/Dt = ρv/ t + u ρv/ x + v ρv/ y + w ρv/ z Dρw/Dt = ρw/ t + u ρw/ x + v ρw/ y + w ρw/ z (non-linear terms) Equation of Continuity: u/ x + v/ y + w/ z = 0 Let u = û + u, where û is the average velocity and u is the periodic velocity due to waves Near bottom velocities peak when waves pass by 2

3 Factors controlling wave height Littoral drift cells 3

4 Shoreline types in Puget Sound Common types of shorelines in Puget Sound: Sand and gravel Sandy beach/dunes Sediment-starved beach Beach w/ bulkheads Mudflats Deltas Armoring of Puget Sound shorelines Shoreline development and armoring: 32% of historic intertidal wetlands lost 73% historic subaerial wetlands lost 30% of shorelines stabilized by structures 1.7 miles armored each year King County: ~ 80% of shorelines armored Requests to repair existing bulkheads require a Shoreline Substantial Development Permit Exemption (SSDPE) modified from Griggs, et al

5 Effects of beach alteration on habitat characteristics and invertebrate densities in Puget Sound Wrack along Puget Sound beaches (Heerhartz et al. 2014) Sobocinski et al. Estuaries and Coasts, 2010 Invertebrates along the Duwamish River Estuary (Seattle). Morley et al Scales of change due to armoring Importance of nearshore zone High productivity Erosion control Water-quality control (nutrient cycling, bioreactivity) Wildlife habitat Habitat mosaic enhances biodiversity Natural resources Asthetics Dethier et al

6 Primary productivity biomass (g dry m-2) productivity (g dry m-2 yr-1) NEARSHORE ESTIMATED TOTAL ANNUAL NET PRODUCTION OF PRIMARY PRODUCERS IN HOOD CANAL brackish marsh macroalgae eelgrass & epiphytes benthic microalgae salt marsh phytoplankton From Simenstad 2004 (Simenstad and Wissmar 1985) Sediment supply to Puget Sound beaches Most beaches sediment starved > 80% of sediment delivered to the Sound by streamflow comes from the 3 rivers: the Skagit, the Puyallup, and the Snohomish. Deltas in protected embayments trap the sediment. Sediment in much of Puget Sound is delivered by coastline erosion and landslides Coarse-grained sediment remains. Fine-grained sand (important for seagrass beds) is more easily eroded. Critical erosion velocities often attained during wave passage Nearshore habitat usage Forage fish for salmon and rockfish: Pacific herring, surf smelt and Pacific sand lance Depend on nearshore marine habitats for spawning and rearing. WDFW enforces No Net Loss regulations for the protection of known forage fish spawning sites 6

7 Nearshore habitat usage Surf smelt spawning beaches Sand lance: spawn on sand beaches Surf Smelt: Spawn in upper intertidal zone on sand and gravel beaches at high tide Herring: Spawn in lower intertidal and upper subtidal regions of bays and sheltered beaches Longfin smelt (Spirinchus thaleichthys) is present but less common in Puget Sound Sand lance spawning beaches Herring spawning grounds 7

8 Shoreline factors affecting spawning success Riparian habitat: Shading, detritus and debris increase spawning success. Riparian vegetation affects nearshore sediment supply Freshwater seeps thought to help spawning Stormwater outfall pipes Bulkheads and seawalls: bury upper intertidal zone, reduce sedimentation, increase erosion, leading to beach armoring and reduced spawning habitat 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 Nearshore use by salmon species Surf smelt and sand lance spawning areas in Bellingham Bay (Williams and Thom 2001) 8

9 Nearshore use by other fish species Eelgrass (Zostera marina) and Hood Canal chum salmon Migratory corridor Predation refuge Foraging habitat (Williams and Thom 2001) NearPRISM Puget Sound Shorelines 9