Morphological changes of tidal flats at the German North Sea Coast induced by tidal asymmetry

Results of an investigation aimed at the morphodynamics of tidal channels and flats are summarized in this paper. The investigation area is the Dithmarschen District on the German North Sea coast, characterized by a mean tidal range of 3.2 in, being widely tide-dominated. The main objective of this study was to evaluate short to middle-term morphological changes and, on the basis of measurements on hydrodynamics and geology, explain the observed patterns of modifications. Periodic bathymetric measurements were carried out at pre-selected channel cross-sections and reveal important morphological changes, which can be summarized in two main trends, including a gradual lateral migration of the channels and a seasonal cycle of erosion (autumn to winter) - deposition (spring to summer). Current measurements over entire tidal cycles were also carried out in several surveys, in different periods at the pre-selected cross-sections. These measurements show important lateral asymmetric pattern for ebb and flood currents that, combined with seasonal variations in the hydrodynamic regime, explains the observed morphological changes. Particularities of the morphological changes at each evaluated cross-section are related with especial geological and morphological characteristics of each area, which were also evaluated due to cores, seismic and side scan sonar.