Sustainable groundwater extraction in coastal areas: a Belgian example

Water extractions in coastal areas have to deal with salt water intrusion and lowering of hydraulic heads in valuable ecosystems. Therefore, sustainable management of fresh water resources in these areas is crucial. This is illustrated here with two water extractions in the western Belgian coastal plain which extract groundwater from a phreatic aquifer in the dunes. One water extraction has problems with salt water intrusion while lowering of hydraulic heads is an issue for both. To remedy the salt water intrusion, it was found that decreasing the extraction rate was the only solution. To offset this and to increase hydraulic heads around both extractions, it was decided to artificially recharge the aquifer of the second extraction with tertiary treated wastewater. By taking these interventions, the combined production capacity of the water extractions was increased with 56% whereas 27% less water was extracted from the dune aquifer itself. Problems and the effects of interventions are illustrated for both water extractions with water quality data and fresh water head observations. A more detailed insight in groundwater flow and fresh-salt water distribution in the aquifer is provided by simulating the evolution of the water extractions with a 3D density dependent groundwater flow model