Asymmetric Morphodynamics of the Wadden Sea

Shallow coastal systems with tidal flats and barrier islands are valuable assets to coastal protection and unique habitats for thriving biodiversity. Sea level rise threatens to diminish these systems unless sediment accretion compensates submergence. To quantify dynamics, an observed geomorphologic time-series was created and assessed over three decades for the world’s largest channel-shoal system, the Wadden Sea. We found that (i) accretion-erosion was asymmetric from deep to shallow, (ii) noteworthy topographic steepening occurred, and (iii) the morphological evolution was systematic across tidal basins. Peak accretion was observed below the tidal low and above tidal high water, while the greatest erosion was found at intermediate subtidal elevations. Most intertidal areas accreted proportional or faster than sea level rise and accretion was prominent at the channel-flat and flat-marsh interfaces. The simultaneous deepening of tidal channels leads to topographic steepening. Overall, the current net sediment import of the Wadden Sea is 19.7 Mm³/yr.