Effects of beach nourishment on seawater intrusion in layered heterogeneous aquifers

•Field data showed groundwater salinity increase after beach nourishment.•Beach nourishment of heterogeneous aquifers creates complex fresh-saline interface movement.•Beach nourishment can merge layered heterogeneity and cause severe groundwater salinization. Beach nourishment is a widespread coastal management technique, which can not only counteract coastal erosion, but also changes coastal groundwater dynamics. Understanding mechanisms and drivers of this subsurface flow and transport processes is key to predicting future groundwater resources to beach nourishment. We implemented a monitoring network of specific conductivity (SC) sensors in wells at different aquifers layers before and after beach nourishment. Recorded SC show that groundwater salinity increased differently after beach nourishment at multiple depths. We used a series of variable-density groundwater flow and salt transport models with both homogeneous and layered heterogeneous cases to illustrate characteristics of groundwater salinity after beach nourishments. Simulations showed that in homogeneous aquifers, salinization patterns were simple and linear related to the beach depth and width, with a relief effect on seawater intrusion. In heterogeneous aquifers, salinity patterns were much more complicated, and the resulting effects on seawater intrusion were determined by the breakdown of original layered system. The analysis provides new insights into the effect of beach nourishment on seawater intrusion. Consideration of aquifer heterogeneity can be a starting point for more sophisticated groundwater management, including vulnerability assessment and optimization of beach nourishment.