Quantifying sediment dynamics within the Dutch Wadden Sea using bathymetric monitoring series

Abstract

Vonhögen-Peeters, L.M., Van Heteren, S., Wiersma, A.P., De Kleine, M.P.E. and Marges, V.C., 2013. Quantifying sediment dynamics in the Dutch Wadden Sea using bathymetric monitoring series.During the last millennium, human intervention has had an increasing impact on the bathymetry of the Wadden Sea. The significance of these human-induced changes for the decadal-scale development of the Wadden Sea in light of natural sediment dynamics is still unknown. We compared a series of 20th-century bathymetric grids and the top of the Pleistocene to calculate the decadal- to millennium-scale net sediment dynamics within the study area. Mean annual net sediment dynamics as determined from these comparisons is dependent on the time period considered. It is as high as 53 million m3 for 1999–2006, the shortest period considered, but less than 3 million m3 for the entire Holocene. The annual increase in accommodation space within the present confines of the Wadden Sea, resulting from relative sea-level rise, local subsidence related to gas extraction, sand and shell mining, and increases in tidal amplitude, is less than 10 million m3. A comparison of this relatively small volume with calculated short-term annual net sediment dynamics shows that processes transporting sediment in the Dutch part of the Wadden Sea are easily capable to fill new accommodation space. The main factors governing long-term system resilience are the availability of sediment in source areas outside the tidal basin and the capacity of inlets to import this sediment at sufficient rates. Large-scale nourishment is carried out to prevent the Wadden Sea from cannibalizing adjacent island heads and ebb-tidal deltas. The present study may help in fine-tuning this regional nourishment strategy.