Interactions of Large-Scale Groyne and Tidal Inlet Migration

The East Frisian tidal inlets tend to migrate with the prevailing eastward drift in the southern North Sea. For Harle inlet eastward migration was accelerated by the adaption of tidal basin and inlet to the resedimentation of a medieval storm surge bay. To prevent further migration a large-scale groyne was built in the eastern part of Harle inlet between 1938 and 1940. Nowadays this structure still keeps the main channel in position and restricts the extent of a secondary channel. But in the last two decades redistribution of tidal gullies in the catchment area significantly increases the tidal prism of the secondary channel and accordingly its cross-section starts to expand. Investigation in light of empirical equilibrium conditions indicate that the partial cross-sections in Harle inlet show a retarded adjustment to the modified hydrodynamical conditions. But future adaptation of equilibrium conditions through further erosion of the secondary channel is anticipated.