Multidecadal Shoreline Changes in Denmark

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Abstract

Multidecadal shoreline changes along ca. 7000 km coastline around Denmark were computed for the time interval between 1862 AD and 2005 AD and were connected with a geomorphological coastal classification. The shoreline data set was based on shoreline positions from historical and modern topographic maps. Coastal landforms were identified on a digital terrain model in combination with aerial photographs. Two shoreline-change computation methods were evaluated at a test site, aiming for optimized time efficiency and accuracy of the countrywide application: a Nearest Neighbor search and a cross-shore transect method based on the ArcGIS-based Digital Shoreline Analysis System (DSAS). The cross-shore transect method was more robust and performed better in the detection of local extremes in shoreline changes, which was crucial for the scope of the mapping. Countrywide shoreline-change distances and rates were, therefore, computed with the DSAS method. Patterns in coastline dynamics were identified through the connection of shoreline-change rates with the occurrence of coastal landforms. Short-term changes and alterations of shoreline evolution through coastal structures were not resolved in this study. Because of the long time span covered, the relative errors originating from data and method are acceptable. The scope of the mapping was to provide a coastal management tool that allows screening for critical sites with respect to coastal erosion. As the first countrywide quantification of historical shoreline changes around Denmark, the mapping can contribute to enhanced adaptation and mitigation strategies in response to increased risks of erosion and flooding under a changing climate.

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