The Wetted Bound: The Missing Link between Surveying and Planning?

by Lesley Ewing, California Coastal Commission, San Francisco, United States,

Document Type: Proceeding Paper

Part of: Coastal Zone '93


Aerial photographs of the coastline are useful tools for investigating historic shoreline changes, especially in locations where such photographs are available back to the late 1920's. From aerial photographs, it is possible to locate many prominent shoreline features such as cliff edges, dune vegetation, the water line, and the wetted bound (the visual demarcation between wet and dry sand). Review of historic photographs allows a qualitative analysis of changes to shoreline features, but most of the classic coastal survey points, such as mean high water, mean sea level and mean lower low water are based on vertical elevations and are difficult, if not impossible, to locate on two-dimensional aerial photographs without pre-established vertical controls. One feature which may offer some link between the visual components of the shoreline and the vertical survey points is the wetted bound where the landward extent of the wetted bound is a function of the height of the previous high tide and of wave runup. Knowledge of the tide range when the aerial photograph was taken will enable coastal scientists and planners to estimate the vertical position of the visual wetted bound and link information from aerial photographs more closely to classic coastal surveys. With a modification for tidal elevation, the wetted bound from aerial photographs can be used as supportive evidence to establish the ordinary high tide line, to better understand long-term shoreline trends, and to evaluate seasonal shoreline trends.

Subject Headings: Tides | Geomatic surveys | Two-dimensional analysis | Aerial surveys | Topographic surveys | Sea water | Hydrographic surveys | Cliffs

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