Geophysical measurement techniques provide powerfull means to visualize the distribution of freshwater in the subsurface, which may otherwise remain hidden. Key to the detection of infiltrated freshwater in the coastal, brackish subsurface forms the water's electrical conductivity (EC). The native groundwater is marked by relatively high ECs as consequence of high salinities, whereas the freshwater is marked by (extremely) low ECs. This difference in EC is ideal for mapping freshwater underground. The different measurement techniques applied are able to measure the EC in the subsurface, which is largely controlled by the EC of the water present in the pores. Decreasing ECs therefore indicate zones of freshening and the build-up of a freshwater reserve.
The measurements were executed by experts of Acacia Water in collaboration with KWR at the reference sites of the Freshmaker (Ovezande) and ASR-Coastal (Nootdorp/Westland) and at the replication site Dinteloord. At all sites, a clear increase in freshwater presence was observed, indicating significant volumes should be readily recoverable with the dedicated SWS set-ups in the coming months.