Analysis of Long-Term Changes of a Sandy Shoreline Utilising High-Resolution Aerial Photography
The Wadden Sea is the shallow sedimentary coastal zone of the south-eastern North Sea. It is a highly dynamic system where shorelines are continuously changed by wind, waves, currents and tides. These morphodynamics were surveyed at the island of Sylt which is located in the northern Wadden Sea. The base of this long-term study is a series of high-resolution aerial photographs from 1928 to 2003. The analyses of the georeferenced aerial photographs and the quantification of shoreline changes were conducted with a Geographic Information System (GIS).
The northern part of the island of Sylt turned out to be the most interesting area where different coastal processes can be observed. The west shore of northern Sylt is subject to severe erosion as it is exposed to strong westerly winds, a consistent westerly wave wash and strong currents. Therefore, a considerable coastal retreat was observed here. In contrast to this, the north shore turned out to be an accumulation area. However, the east shore of northern Sylt is rather inactive due to its sheltered position as well as solid coastal protection constructions, such as dykes and petrified coastal sections.
In order to compensate the coastal retreat at the west shore, sand replenishment is carried out almost annually since 1972. By this, the loss of sand gets compensated and the shoreline could be fixed. At the same time, the annual accumulation rates at the north shore increased considerably. Due to the sand replenishment at the west shore, a lot of unconsolidated material is artificially supplied to the depositional system. These sediments get transported to some extent to the north shore of Sylt where they are deposited.
High-resolution aerial photographs and their analysis with GIS proofed to be very suitable to monitor coastal processes and the efficiency of coastal protection measures, like sand replenishment. This technique is a powerful method to detect erosion “hotspots”. It can be especially recommended for long-term and local surveys at a smaller spatial scale.
KeywordsShoreline changes GIS Aerial photographs Wadden Sea Sand replenishment
Christian Hass (AWI), the Regional Office of the Schleswig-Holstein Wadden Sea National Park, Toenning (NPA) and the Regional State Office for the Rural Areas, Husum (ALR) are gratefully acknowledged for providing aerial photographs. My thanks to G. Gayer from the GKSS for supplying the current model and special thanks to Trevor Vincent for proof-reading.
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