Transport of Fine-Grained Sediments in the Dutch Coastal Zone

Abstract

This paper discusses the effects of a change in discharge regime of the River Rhine on the cohesive sediment transport in the Dutch coastal zone and towards the Wadden Sea. Two 3D numerical models are used to quantify these effects in a comparative study. It is shown that a different discharge regime may influence the sediment concentration in the Wadden Sea. INTRODUCTION Large amounts of fine-grained, cohesive sediments are transported in the Dutch coastal waters, estimated at 10 to 60x106 ton/year. This transport is confined to a nearshore coastal zone of 10 to 20 km width, the so-called coastal river, as a result of a balance between Coriolis effects and a cross-shore gravitational circulation, induced by the outflow of the River Rhine. A proper estimate of the total flux of fine-grained sediments, their pathways for transport and fate is important, as 9 these sediments cause large siltation, hence require costly maintenance operations, in the harbour basins and navigational channels in the coastal zone (e.g. the Port of Rotterdam); and 9 these sediments have a key contribution to the ecological functioning of the Wadden Sea in the northern part of The Netherlands, Germany and Denmark. The present paper describes a three-dimensional numerical model to calculate the transport and fate of these sediments, with emphasis to the effects on the Wadden Sea. The numerical model (hereafter SNS-model) covers the entire southern part of the North Sea, including the Strait of Dover, the Wadden Sea and the German Bight, on a 1) WLIdelft hydraulics, PO Box 177, 2600 MH Delft, The Netherlands, tel: 31-15-2858839, fax: 31-15-2858582, email: Thijs.vanKessel@wldelft.nl, 2) Expert Centre for Project Mainport development Rotterdam 3) also Delft University of Technology, Faculty of Civil Engineering and Geosciences.