Global assessment of the potential effect of large sand replenishment on fresh groundwater resources

Sand replenishments, or nourishments, have been the prevalent strategy of the Netherlands for coastal protection since 1990. In consideration of the expected sea level rise and potential increases of storm surges as a result of climate change, an innovative pilot project known as the ‘Sand Engine’ has been implemented. In contrast with traditional replenishments that are repeated with 3 to 5 year intervals, this local mega-nourishment is expected to protect the coastline for a period of at least 20 years. As sand replenishments are a widely applied technique, the concept of the Sand Engine, if proven successful, could be an effective solution for other areas of the world as well. This study looks into the potential effects of a large-scale sand replenishment on fresh groundwater resources, on four coastal areas in different parts of the world where such a project could be applied. These effects were quantified using 2-D variable density groundwater flow and coupled salt transfer models, by simulating the fresh-saline water interface before and after the replenishment, and comparing the results based on the current sea level and weather conditions with those based on scenarios of climate change. The results show that a large sand replenishment can lead to a considerable increase in the fresh groundwater volume, offering an opportunity to combine coastal protection with an increase of freshwater availability for areas with limited water resources