Banks and bluffs are steep areas located between the intertidal zone and the upland (Figure IV-9). The ShoreZone Inventory (Washington State Department of Natural Resources 2001) identifies cliffs as those areas with a slope of more than 20% grade. Banks and bluffs can be composed of varying grain sizes of sediment and rocks and boulders. As described in more detail in Chapter III, these habitats are formed and maintained by the dynamics of numerous factors, including soils, wind, erosion, hydrology, and vegetative cover (Table IV-8).
The “health” of banks and bluffs is difficult to assess. We do know that stressors include shoreline armoring, removal of native trees and shrubs, shoreline development, overwater structures, dredging, filling, sediment extraction, and hydrology changes. |
Residential development can cause erosion and stability problems, and landslides have been documented over the past few years. In general, a change in the erosion rate of these areas would affect not only the protection of the upland area, but also the sediment composition and elevation of beaches and other intertidal and shallow subtidal habitats. Hence, where bank erosion rates have been increased or where erosion has been interrupted by artificial means (e.g., a bulkhead), the health of the adjacent habitats that are dependent on sediment from the bluffs is affected. The maintenance of these areas is dependent on a source of sediment from eroding bluffs.
The historical distribution of banks and bluffs has not been mapped, although the major obvious changes are likely shoreline armoring and coastal development that directly affect bluffs and their maintenance processes. A number of eroding bluff areas have been identified, including shorelines south of Agate Pass, at Battle Point, north of Fletcher Bay, near Blakely Harbor, near Yeomalt Point and Ferncliff, around Skiff Point to Madison Church, and west of Madison Bay near Agate Point (Geologic Stability Map, Appendix A). |
