Sand spits are relatively rare and unique features in Puget Sound (Table IV-6). They may enclose (partially or totally) intertidal estuarine areas. Substrata are typically sand, silty sand, or gravelly sand (Figure IV-7).
Figure IV-7. Sand spit, marsh and lagoon at Battle Point (© WA Dept. of Ecology 1992).
|
| Table IV-6. Sand Spit Habitat |
Diagnostic species:
Dune grasses
Salt marsh species
Common Associates:
Dunlin (Calidris alpina)
Sandpipers (e.g., Caladris mauri)
Various mammal species
Distribution:
Supratidal, form embayments
Functions:
Foraging and nesting areas for waterfowl and shorebirds
Prey production for crabs, sculpin, flatfish
Bivalve production
Primary production
Factors controlling functions:
Currents and wave dynamics
Erosion and deposition forces
Stressors:
Unnatural erosion or deposition of sediment
Physical disturbances from shoreline armoring, marina construction |
|
Low salt marshes can dominate the upper zones of these estuarine, intertidal marsh areas on the protected/landward side of spits. Sediment particles contributing to sand spit formation on Bainbridge Island originate primarily from eroding bluffs. Waves and currents transport this material along the shoreline until it settles out near an embayment, forming a spit. Changes in stream sediment load, tidal currents, and wave action can affect the maintenance of sand spits. Because the sand spit is a protective structure, the embayment behind the spit can develop a marsh/flat/channel system with function similar to those described for these habitats above. Spits are vulnerable to erosion during extreme storm events, and may be overtopped and breached. With appropriate sediment sources, they rebuild rather rapidly. In situations where sediment supply is restricted, spits may erode and not recover.
Several spits are present on Bainbridge Island, including Point Monroe, Battle Point, Fletcher Bay, inner Eagle Harbor, Agate Point, and Wing Point. |
