Projecting Hydro-Morphodynamic Impacts of Planned Layout Changes for a Coastal Harbor

Abstract

The macrotidally influenced harbor of Dagebüll on the North Sea coast of Germany features a piled south jetty, for which provided constructive designs are investigated regarding their potential hydro-morphological impacts on the harbor area and adjacent navigational channel. The harbor experiences a steady accumulation of sediment. This results in a reduction of navigational depth and necessitates regular maintenance dredging constituting a cost aspect. A comprehensive field study was conducted, deploying a ridged inflatable boat (RIB) equipped with differential Global Positioning System, a winch for conductivity, temperature, and depth casting as well as sediment and water sampling and an acoustic Doppler current profiler for current profiling. Measurements reveal a tidally governed alternating flow pattern inducing a vortex current inside the harbor basin. Hydrodynamic sea floor grain sorting is detected through sediment sampling. A numerical model cascade is developed and calibrated against available tide gauge and sediment inventory data as well as multibeam survey data and acquired field measurements. The calibrated model cascade is used to simulate layout variants and compare resulting impacts to identify preferable jetty designs.