Effects of global change on heterogeneous coastal aquifers: A case study in Belgium

Coastal plains are in the frontline of climate change. Predicted increase in recharge and sea level rise will alter groundwater flow, water quality distribution, recharge, and discharge considerably. This is simulated here in the Belgian western coastal plain. lt consists of a shore, dunes, and polder (low-lying area) with a heterogeneous groundwater reservoir of quaternary age. A three-dimensional density-dependent groundwater flow model based on numerous (hydro)geologic observations was made. First the current groundwater flow and distribution between fresh and salt water was simulated. Then the effects of a 15% recharge increase and 0.4 m of sea level rise in the next 100 years were modelled. Sea level rise results in an increased flow of fresh water toward the polder and a decreased flow toward the sea. An increase in recharge results in more water flowing toward both the polder and the sea. Brackish water present in the polder will be pushed back as is a current saltwater intrusion from the polder in the dunes. The simulations also show that groundwater levels will rise. This will put strain on the ecologically valuable dunes and the drainage system in the polders.