Shoreline Stewardship

IV. B. 7. Beaches and Backshore

A beach is an accumulation of unconsolidated material formed by waves and wave-induced currents in the zone that extends landward from the extreme lower low water line to a place where there is a marked change in material or physiographic form, usually the effective limit of storm waves (Figure IV-8).  Beaches include cobble, boulder, sand, and silt areas that comprise most of the shoreline of Puget Sound.  They are generally steeper than tide flats described above (Table IV-7).

Functions supported by beaches are numerous, and are generally similar to those described above for tide flats.  However, the level of each function differs from tide flats. Cobble beaches, especially in lower energy environments, can contain large abundances of bivalve shellfish.  Densities of clams, such as butter (Saxidomus giganteus) and littleneck (Tapes japonica), can be as great as several hundred per square meter.  Production rates on cobble shorelines can be as high as in eelgrass meadows (Thom et al. 1984).  Beaches with finer sediments from pea gravel to coarse sand also can contain extensive shellfish abundances.  In addition, these beaches are known to provide optimal spawning habitat for forage fish, such as sand lance and surf smelt (Penttila 1996).  It has been shown that forage fish egg survival is partially dependent on moisture retention in the sediment, as well as the shade from overhanging vegetation.  Alteration of groundwater flows that surface in the intertidal zone, for example by armoring shorelines, in addition to loss of shade can result in dryer conditions that may reduce egg survival (Levings and Jamieson 2001).  Loss or alteration of forage fish spawning beaches is a major concern among resource managers.

Backshore areas are immediately landward of beach face and are zones inundated only by extreme storm-driven tides (Figure IV-8).  Backshore areas have not been studied as well as beaches for their ecological functions.  However, we do know that woody debris accumulates in the backshore through transport at extreme high tides.  It is generally believed that this woody debris can help stabilize the shoreline and provide microhabitats for invertebrates and birds.  Backshore areas also support a unique assemblage of vegetation tolerant of wind, salt spray, and shifting substrate. 

Shoreline armoring, loss of riparian vegetation, overwater structures, dredging, filling, and resource harvesting are likely the major causes for loss of beach and backshore habitat.  Although beaches on Bainbridge Island typically have backshore zones with narrow to no width, these areas can be found contributing to beach habitat on the Island, most notably at Point White (and the area south of Point White), Yeomalt Point, Pleasant Beach area, Crystal Springs, parts of Manzanita and Fletcher Bays, inside Wing Point, and south of Agate Pass.