Equilibrium-Type Response Model for the Sediment Volume of Dredging and Disposal Areas

Abstract

Measured time series of the sediment volume of dredging and disposal areas in the Scheldt estuary of the Netherlands and Belgium are presented and compared to an equilibrium-type response model. The model is based on the assumption that the sediment volume removed from a dredging area returns through siltation at a rate proportional to the difference between the current sediment volume and a time-dependent autonomous equilibrium volume. For disposal sites, a similar assumption is made regarding the rate at which the dumped sediment disappears through erosion. The model contains three fitting parameters for disposal areas or two parameters for dredging areas and was fitted to observed sediment volume time series of five disposal sites and eight dredging areas in the Scheldt estuary, for which frequent bathymetric surveys were conducted as part of the flexible disposal management plan. Model results indicate that sediment dumped in disposal areas has a half-life residence time of 179–409 days, and dredging areas show shorter response times of 0–187 days. Results also show that, following a disposal event, the observed sediment volume on the bed is typically smaller than what is estimated based on hopper volumes. The model can also be used to forecast future sediment volumes as a result of planned dredging or disposal campaigns and thus can serve as a decision-making tool for estuary managers.