Intertidal Topographic Maps and Morphological Changes in the German Wadden Sea between 1996-1999 and 2006-2009 from the Waterline Method and SAR Images

The Dutch, German, and Danish Wadden Sea is one of the largest tidal flats in the world which has been left in a nearly natural state. Several studies generated the topography of this valuable area, but presented only single maps, which covered partial regions of the Wadden Sea. The objectives of this paper are 1) to use the waterline method to analyze SAR images in order to generate annual topographic maps of the northern parts of the German Wadden Sea for the years 1996-1999 and 2006-2009 and 2) to quantitatively estimate and monitor the development of the tidal flats. The waterlines are detected by a wavelet-based edge detection algorithm, geocoded in Gauss-Krueger coordinates, assigned with water level information, and interpolated into topographic maps. Our results show the development of the tidal flats over the 8 years and illustrate three of the most changing regions: Tertiussand, Gelbsand, and Medemsand. Their area, shape, and sediment volume have changed significantly due to the tide, wave, wind, and river discharge influences. The waterline method is an efficient and economical way to monitor large tidal flat areas, which allows an estimation of long-term morphological development. One potential application is to assimilate the results into morphodynamic models in order to give finer morphological predictions.