Assessment of Saltwater Intrusion Vulnerability in the Coastal Aquifers in Ninh Thuan, Vietnam

Abstract

As surface water has declined under climate change conditions and human activities, groundwater has become the most important source of water supply for Ninh Thuan province, which is one of the most arid regions of Vietnam. The increase of groundwater extraction and sea-level rise has brought about increase in seawater intrusion, which has become the biggest concern for the groundwater resources of this coastal area; thus, it is necessary to evaluate the saltwater intrusion vulnerability in aquifers for planning and sustainable exploitation of groundwater in the province. In this study, an overview of the previous fresh–saltwater interface studies and updated geophysical investigation (Vertical Electrical Sounding – VES) was carried out to understand the situation or status of the salinity of groundwater. Besides, chemical compounds of water sources were also analysed to clarify the recharge sources and origin of saltwater in the aquifers. Based on collected and field survey data, GALDIT method was used to assess the saltwater intrusion vulnerability in the coastal aquifers of the study area with six factors incorporated: groundwater occurrence, aquifer hydraulic conductivity, depth to groundwater level, distance from shore, impact of existing seawater intrusion, and aquifer thickness. The weight of each GALDIT parameter was calculated by analytic hierarchy process (AHP) based on the results of surveys of over 50 hydrogeological experts in Vietnam to calculate the GALDIT index for the final saltwater intrusion vulnerability map of Ninh Thuan coastal aquifers.