In order to improve flood prevention, sand nourishment is used as an effective tool to reinforce the Hondsbossche sea wall. As new dunes develop, this is likely to lead to a reduction of saltwater seepage. This reduction will have its effects on the saline and brackish ecosystem in the area behind the Hondsbossche sea wall. The Hollands Noorderkwartier Higher Water Board commissioned Acacia Water to conduct a study monitoring the groundwater and surface water. This study provided insight into the developments of the ecosystem and the impact of coastal reinforcement. With the help of a variety of geophysical methods, we were able to assess this impact.