Quantification of morphodynamic variability and sea state damping of plates at the nearshore area in the East Frisian North Sea

Abstract

At the nearshore area of Norderney, the ebb-tidal delta (ETD) sandbanks exert a huge impact on the local wave climate, which is of particular interest for coastal protection. Besides an eastward migration of the sandbanks with a mean velocity from 435-491 m/y, depending on the plates position, the ETD sandbanks had a high variability in shape and size. Therefore, the influence of those morphodynamic changes on the sea state damping effect was quantified by dynamic bathymetries using validated SWAN simulations. The impacts of the bathymetries from the years 1995, 2005, 2006, 2008, and 2015 with highest morphological variability were considered for five different boundary conditions, representing storm surge events of the Norderney nearshore wave climate. A mean variation of 14 ± 2% of the relative sea state damping effect was found for the different bathymetries of the ETD sandbanks at the various boundary conditions. Swell waves showed a range of 16 ± 2% for the damping effect, which increased with increasing incoming wave height. Buoy data off the Norderney coast from 1992 to 2017 were investigated and a mean buoy-measured damping effect of 0.37 was determined over the entire period. General results of SWAN modeling were also found in the in-situ measurements.