Sediment transport through the Eastern Scheldt storm surge barrier

Abstract

The aim of this research is to determine to what extend the scour holes limit the sediment transport through the Eastern Scheldt storm surge barrier and whether or not human adaptations, like sand-nourishments in the scour holes, can have a positive effect on the sediment import. To investigate these scenarios a numerical model (Delft3D) is used to study the tide-induced flow and sediment transport in and around the scour holes and the storm surge barrier. The two most important conclusions resulting from the analysis on the vertical processes in the scour holes are: (1) A vertical flow recirculation develops behind the barrier-sill, but no vertical flow recirculation inside the scour hole is expected and (2) The hydrostatic model with a $\sigma$-coordinate layer distribution in Delft3D shows significantly higher flow velocities at the bottom of the scour hole than the model with a (hydrostatic and non-hydrostatic) Z-coordinate layer distribution. Due to a lack of field-measurements it is difficult to determine the accuracy of both models, but the differences can be of importance when a 3-dimensional model is constructed in the future. In the analysis on the horizontal transport patterns around the Roompot inlet, the 2DH model results show mainly import of sediment from the south-western channel during flood and large seaward-directed transports through the northern part of the inlet during ebb. In this way the seaward scour hole forms a blockage of the sediment transport from the ebb-tidal delta towards the storm surge barrier. At the eastern side of the storm surge barrier, much smaller net sediment transport rates are found compared to the seaward side. In the scenario analysis, all model runs show a trend where the adaptations mainly increase the net sediment transport in the direction of the ebb-tidal delta, rather than transport towards the basin. Also, the absolute net yearly transport rates are very small compared to the total sand demand of the Eastern Scheldt to reach a new equilibrium. Although the model results contain some uncertainties and improvements have to be made, one conclusion from the present study is that the studied scenarios do not seem to be very efficient measures in order to significantly decrease the sand demand of the Eastern Scheldt on a short time scale.