GIS based – GALDIT method for aquifer vulnerability assessment to seawater intrusion: Case of a qp2-3 aquifer of Mekong Delta

Abstract

Recently, seawater intrusion (SWI) in coastal aquifers is a global issue that is exacerbated by sea-level rise, climate change, and an increasing dependency on coastal fresh groundwater resources for water supply. Vietnam's Mekong Delta has a flat topography, a dense river network, and a 700 kilometer coastline covering the region's west and east. The Mekong Delta is facing increasingly serious saline intrusion. This paper describes the results of the examination using the GALDIT method as a model to evaluate the vulnerability of seawater intrusion. The method is used to determine the trend of groundwater contamination by seawater intrusion in the qp2-3 aquifer of the Mekong Delta, this Upper-middle Pleistocene aquifer (qp2-3) is one of the main productive aquifers in the Mekong Delta. The analysis result in 2015 shows a moderate and high level of vulnerability in which the highly vulnerable area is along the Tien River and at the depression cone area in Ca Mau. The analysis is reconducted for the time of 2030 with the predicted values for the groundwater level through the forecasting tool. By comparing the model of two times of 2015 and 2030, the results indicated that the impact of the continuous decline of groundwater level is greater than the impact of sea level rise. If the rate of drawdown is kept the same, by 2030 the highly vulnerability area will have expanded to two-thirds of the Mekong Delta. The GALDIT method is a good approach for saltwater intrusion research and moreover water management, and environmental management, such as evaluating the most sensitive areas for monitoring or imposing restrictions where necessary.