A sediment budget for a highly developed coast – Belgian case

Most of the world's beaches are endangered by a lack of sediment, anticipated increase in storminess, and accelerated sea level rise. The sediment budget is a useful tool for understanding and quantifying the impact of these threats to a particular coast. This study presents a sediment budget for the short, but highly developed Belgian coast. Various contributors to the sediment budget were considered in this study. A 10-year timescale was selected, as the hydrodynamic forcing and sediment input are relatively homogenous over longer timescales. The nearshore system, confined offshore by the closure depth and onshore by human structures, was divided into 9 coastal cells, mainly based on the variations in the gradients of the longshore transport. These cells were analyzed using available information such as bathymetric and topographic surveys, placement and removals of sediment by human intervention, sediment deficit created by sea level rise, and estimates of longshore transport. This is the first sediment budget developed for the entire Belgian nearshore system. The coastal sediment budget is generally balanced, with the exception of the area downdrift of Zeebrugge harbor. However, this was expected due to the large disturbance induced by the harbor breakwaters, which extend approximately 3.5 km offshore. The accuracy of the sediment budget can be increased in the future by improving the accuracy of the models used to estimate the along- and cross-shore sediment transport rates, especially investigating the role of the sand banks in the nearshore sediment dynamics