Abstract:

Coastal aquifers constitute an important high-quality freshwater resource exploited for agriculture, industry and human consumption. An increase in salinity occurs close to the sea, highlighting the need to investigate the water balance and groundwater behavior. Normally, this task could be solved by using monitoring data and groundwater modeling. The main difficulty is to parameterize and calibrate/validate the variable-density modeling. This requires adequate information on aquifer parameters and concentration distribution in groundwater. To solve this problem, we propose to use geophysical investigations to describe and image the transition zone of the freshwater/saltwater. Based on the apparent resistivity/conductivity values obtained from electromagnetic (EM) investigations, 3D saltwater distribution was characterized for study area. Saltwater were found from 4- 5 m.asl close the southwest boundary to more than 20 m.asl near boreholes X34, X35 (about 1.7km from the boundary). In marsh area near the surface confirming the presence of a top clay layer and the salinity of surface water caused by evaporation. Such investigations can help to setup and validate the variable-density flow models. Electromagnetic method has been applied successful to determine saltwater intrusion in groundwater in Crau aquifer, southeastern France, where hydrological characteristics are similar to coastal aquifers in Vietnam