3.1.2 Limiting Factors and Opportunities |
The average normalized controlling factor (CF) score of all reaches Island-wide was ‑0.45 (median -0.48, range: -0.87 to 0.00), whereas the average of all normalized MA scores was -0.44, (median -0.47, range: -0.56 to -0.30) (Table A-2; Figure B-10). The values above represent baseline scores over all of Bainbridge Island for relative comparison with individual MAs and reaches, which are discussed in detail below. The most highly impacted MA on Bainbridge Island is Eagle Harbor (MA-5; CF Score -0.56), which also included some of the most highly disturbed reaches over the study area (Figure B-12, Figure B-13, Appendix C). The least-impacted MAs are Murden Cove (MA-4; normalized CF Score -0.33) and Blakely Harbor (MA-6; normalized CF Score -0.30). Scores of documented ecological functions (EF) were highest in Manzanita Bay (MA-9; EF Score 23.9), Agate Passage (MA-1; EF Score 28.4), and Port Madison Bay (MA-2; EF Score 23.0), the northern portion of Bainbridge Island (Figure B-11, Appendix D). In contrast, the lowest EF Scores were observed in Eagle Harbor (MA-5; EF Score 17.9), Blakely Harbor (MA-6; EF Score 17.6), and Rich Passage (MA-7; EF Score 16.1). Prioritization methods for best determining management options based on these results is discussed in Appendix E; Figure B-14 provides a graphical display for reference.
Because the analysis involved only data from Bainbridge Island (the population of interest), it is currently inappropriate to make comparisons relative to all of Puget Sound. Bainbridge Island’s diverse shoreline conditions range from polluted urban waterfronts to moderate-density residential development, to fairly undisturbed stretches of shoreline with intact riparian habitats. Therefore, Bainbridge Island represents a microcosm of Puget Sound, with on average, moderate levels of impacts to nearshore resources, but extreme examples of high and low impacts as well (Figures B-12, B-13, and B-14).
On average, the mean raw reach score for individual controlling factor metrics over all Bainbridge Island was -2.10, which provides some basis for distinguishing specific metrics which influenced cumulative scores in a positive or negative direction (Table A-3). Substrate type (-2.90) and depth/slope (-2.61) metrics had the lowest (worst) average scores and represented the most impacted controlling factors over the entire Island (Figure B-15, Figure B-16). Scoring of both metrics was influenced by percentage of shoreline armoring data. As well, the substrate metric reflected the density of all point modifications, whereas depth-slope reflected the relative amount of dredging and armoring encroachment. In summary, the low (poor) scores in these metrics suggest that high rates of shoreline armoring (48% of shoreline), armoring encroachment (25% of shoreline), and point modifications (10.4 structures per 1000 ft shoreline) have significantly changed the historic composition of substrate and depth-slope contours along Bainbridge Island shorelines.
Hydrology (-1.23) and physical disturbance (-1.60) raw controlling factor metrics scored highest (best) and represented the least-impacted controlling factors over all Bainbridge Island reaches (Table A-3; Figure B-15). Scores of both metrics were highly influenced by land cover. As well, the hydrology metric reflects the presence of unnatural tidal constrictions along the shoreline, armoring encroachment, and outfall density. The physical disturbance metric characterized recurring human activities along the shoreline and was also influenced by the presence of urban waterfront activity and the density of floating structures and boat ramps. The relatively higher scores in these metrics suggest that low-to-moderate density residential land use within the marine riparian zone (54% naturally vegetated surfaces, 23% impervious surfaces) has likely helped to sustain some historic level of hydrology function and protection from physical disturbance along many of Bainbridge Island shorelines.
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