Storm Impact on the Coastal Geomorphology and Current Field by Wave Field Image sequences


Basic requirement for the coastal protection and management is the monitoring of the hydrodynamic processes, tidal currents and sea state, as they have direct impact on the temporal and spatial evolution of geomorphology. The current field -regime-and bathymetry changes occurred during episodic events, such as storms, have been proved as effective as the long term physical processes, but still their monitoring is insufficient. The Dispersive Surface Classificator – DiSC is a recent technique that fills this gap to determine spatial maps of hydrographic parameters. It is based on the analysis of nautical X-band radar image sequences of the sea surface waves. In this study, the DiSC methodology is summarized; the post processing approaches and their consistency with echo soundings are presented. The main focus of this study is the demonstration of the method’s capabilities into the frame of a coastal monitoring system of a sand-barrier island which is continuously under eroding pressure. The method is illustrated by focusing on the monitoring of the impact of a 10-day storm on the current field and bathymetry at the littoral zone of the island Sylt in German Bight. The total volume of the moved sediment, within the 5 km2 monitored area for the 10 days period, is estimated in the order of 5 % of the annual sediment budget of the area. The tidal current field was monitored for 3 tidal cycles during which the impacts of the local geomorphology, of the air pressure and of the wind could be identified. The low air pressure eliminated the ebb phase of the current field. The measurements in front of the entrance of the tidal basin proofed the atmospheric pressure gradient has a direct impact on the local current field and dominates the local circulation. In general, the present study illustrates the potential of the ground based remote sensing in monitoring of small-area changes in the coastal environment caused by mesoscale phenomena.
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