III. D. Key Findings and Conclusions |
The general coastal processes that occur around Bainbridge Island have been summarized above. The general characteristics of the factors that influence or contribute to coastal processes have been defined around the Island, but site-specific detail is lacking. The following is a listing of the key findings, observations, data gaps, and resources.
- Bainbridge Island is an eroding system in which the bluffs contribute sediment to the beach, where waves and currents redistribute it along the shoreline. No other sources other than the island supplies material to the beaches. In the long run, storms remove more beach material than is returned to the beach during mild wave conditions. Modifications (such as bulkheads or other bank armoring to “stabilize” the slope) that limit the supply of sand and gravel to the beach will have long-term consequences elsewhere, as will construction measures that modify the natural transport of sand along the shoreline. Detailed mapping of the Bainbridge Island nearshore uplands indicating areas susceptible to erosion (due to groundwater flow, surface water flow, or development) has not been conducted. As individual development projects are considered, site-specific investigations should be required to evaluate the conditions of the local soils and surface water runoff and drainage.
- The directions and rates of sediment transport along the Island’s beaches are the result of calculated wave conditions, which are based on winds measured at a site considerably distant from the Island. Though the results of these studies are useful as large-scale indicators of processes, they may be misleading for particular sites. Site-specific investigations should be considered to reevaluate waves, currents, and sediment transport conditions based on recent developments in coastal engineering technology. The long‑term consequences of the decision or action may also have to take into account such issues as earthquake risk, tsunami inundation and sea-level changes.
- Considerable resources and technologies exist to predict sediment transport caused by waves on Island beaches. The technologies were developed for other locations and should be applied to Bainbridge Island with caution. The differences in conditions between the Island and those for which the technologies were developed should be acknowledged and quantified where possible.
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