Guy R. Gelfenbaum Nicholas C. Kraus William G. McDougal Ann E. Gibbs 1999 <p><span class="EXLDetailsDisplayVal">Historical hydrographic data from the <span class="searchword">Washington</span>/<span class="searchword">Oregon</span> shelf are compared for the first time to identify <span class="searchword">bathymetric</span> <span class="searchword">change</span> on a regional scale. Offshore data sets exist for four time periods: 1800s, pre-1950s, post-1950s, and 1990s. Data from only two time periods, 1868-87 and 1926-27, cover the entire offshore region between Tillamook Head, <span class="searchword">Oregon</span> and Grays Harbor, <span class="searchword">Washington</span>. A confidence interval of + or -1.7 m is established for the <span class="searchword">bathymetric</span> comparison between these two data sets. Wide trackline spacings within the 1868/87 surveys, sounding errors due to horizontal positioning inaccuracies and heavy seas and currents encountered during the surveys, questionable tidal correction methods, and vertical datum inconsistencies, compose most of the uncertainties in this data set. Surveys collected closer to shore, in water depths less than -30 m, contain smaller errors and define the sea-floor morphology well. Errors and uncertainties increase with depth and distance offshore. Comparison between these two surveys shows large areas of both accretion and erosion on the shelf between the shoreline and -70 m of water, with the greatest change occurring off the mouth of the Columbia River. Quantitative analysis and interpretation of the regional bathymetric changes within the Columbia River Littoral Cell should be approached with caution and with a thorough knowledge of the error distribution and uncertainties associated with the data set.</span> </p> application/pdf en Bathymetric change off the Washington-Oregon coast text