Keys to High-Accuracy Mapping of Shoreline Changesby Suleyman Demirpolat, Environmental Science &, Engineering Inc, Gainesville, United States,
William F. Tanner, Environmental Science &, Engineering Inc, Gainesville, United States,
Abstract: For many years it has been difficult to overlay maps and aerial photographs with different scales and publication dates using conventional techniques. Large processing errors also made it difficult to identify low change rates. Intergraph 68000 and Microstation computers and Geographical Information System (GIS) software were used to minimize scale effects and to compare historical shoreline positions with 1.5 m. mean processing error (standard deviation 1.5). Shorelines and bathymetric contours on all available and acceptable maps (1850 to 1988) were digitized, with different line types and colors for each date on the printout. Maps published in the late 1800s based on unknown or unstated datums and later maps based on U.S. Standard and North American Datums were corrected to the North American 1927 Datum. Two different dated inshore and offshore bathymetries were overlayed on each other and subtracted one from another to identify areas of erosion and deposition. These areas were then contoured with different line-types and colors to show offshore sand mobility. Water depths had increased in areas of erosion; therefore, higher wave energy, leading to high erosion rates in the future, can be expected. The data base that is created in this work provides much more information than can be shown on printed maps. It opens new research opportunities, such as the possibility of predicting future erosion.
Subject Headings: Mapping | Erosion | Computer software | Information systems | Shoreline | Geographic information systems | Bathymetry | Geodetic datum
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