2.2.2 Spatial Scale: Defining the Landscape |
Landscape principles were used to define two ecologically relevant spatial scales for conducting the assessment along the shoreline. The first scale uses drift cells to define nine mutually exclusive ecological Management Areas (MAs), which may be considered analogous to upland watersheds (Figure 2). Because drift cells “act as closed or nearly closed systems with respect to transport of beach sediment” (Schwartz et al. 1991), they form the basis for establishing and maintaining habitat structure, ecological processes, and ecological functions. Drift cells may converge (e.g., form points) or terminate into areas considered to lack alongshore drift (e.g., back bays), and therefore coalesce to form larger interrelated systems, just as upland watersheds may include aggregations of smaller watersheds or subbasins. Ultimately, the boundaries between shoreline MAs typically fall where drift cells diverge. Drift cells have been delineated through a series of master’s theses produced at Western Washington University and later republished in a series of reports by the Washington State Department of Ecology (WDOE). The 21 drift cells mapped around Bainbridge Island were first delineated by Taggart (1984) and later republished by Schwartz (1991) (Table 3; Figure 3).
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| Figure 2. Bainbridge Island Management Areas. | Figure 3. Bainbridge Island Drift Cells. |
The COBI, with input from a technical advisory team, used local knowledge to independently review reports for consistency about drift cell direction, and used this information to ultimately define nine MAs (Best 2003). The nine Bainbridge Island MAs are defined as follows:
- MA-1 – Agate Passage
- MA-2 – Port Madison Bay
- MA-3 – Rolling Bay – Point Monroe
- MA-4 – Murden Cove
- MA-5 – Eagle Harbor
- MA-6 – Blakely Harbor
- MA-7 – Rich Passage
- MA-8 – Point White – Battle Point
- MA-9 – Manzanita Bay
At the second landscape scale, shoreline MAs were further broken into “reaches,” which were principally delineated in the ShoreZone Inventory as “ShoreZone Units,” i.e., areas of relatively homogeneous beach geomorphology (WDNR 2001). A total of 198 reaches were defined on Bainbridge Island by the ShoreZone inventory, although by necessity, the total number was increased to 201 by delineating two additional reaches: the Schel-Chelb estuary at Lynwood Center off Rich Passage (Reach 6001) and an adjacent stretch of shoreline (Reach 6000), and the high bluff area inside of the lagoon formed by Point Monroe (Reach 6002). The number of reaches within a particular MA ranged from 10 (MA-9) to 38 (MA-8).
Reaches are segments of longer linear shoreline features and are basically analogous to stream reaches within the context of upland watersheds. The distribution of living resources is largely affected by the local environmental conditions that occur at this smaller geographic scale. For example, the local combination of controlling factors, such as slope, depth, hydrology, and wave energy, defines the type of vegetation and substrate (habitat structure) that occurs in that area. Biological communities, which are often spatially constrained by local controlling factors and habitat structure, serve to further define the structure and functions (e.g., refuge, nutrient cycling) of the nearshore ecosystem.
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