III. C. 3. Seasonal Variations |
During most of the year, the wind-generated waves around Bainbridge Island are quite small and only the fine-grained materials are moved up and down the beaches. During winter storms, however, which tend to arrive from the southwest, sediment transport can be considerable. Strong storm waves originating from the south transport sediment to the north. Most of the sediment transport that occurs in Puget Sound can be attributed to storm events and potentially to vessel transit. If either of these events coincides with a high tide, waves can attack the shoreline at higher elevations, potentially causing increased sediment movement.
Whereas winter storms around Bainbridge Island carry sediment loads alongshore, mostly from south to north and offshore, the summer season experiences northerly winds that induce a north-to-south movement of sediment. During this season, waves exert little energy on the beaches. Smaller waves can return some of the finer sands from offshore back up onto the beaches (Downing 1983). The importance of the seasonal variation in sediment movement varies from location to location. The Coastal Zone Atlas (Washington State Department of Ecology 1979b) details the direction and importance of the littoral transport rates for the winter season and for the summer season. The estimates are based on potential sediment transport rates and on an older version of the Shore Protection Manual. There are no known systematic studies of the rates and directions of annual sediment transport for Bainbridge Island.
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