Groundwater and surface water interaction in Hau River, Mekong Delta: A preliminary investigation

Abstract

This study investigates the interaction between groundwater and surface water in An Phu, An Giang province, an arsenic hotspot in the Mekong Delta. Eight boreholes were installed in the shallow aquifer for hydrogeological investigation and groundwater level monitoring. To quantify the recharge rate, additional data — such as Hau (Bassac) River water levels, rainfall, evaporation, temperature, and groundwater abstraction rates — were collected to generate a high - resolution 3D groundwater flow model. The model was then calibrated using the PEST tool under both steady - state and transient conditions. The results show that the shallow aquifer is semi - confined, allowing surface water to infiltrate directly into the aquifer system. Recharge flux varies by location and time, ranging from 0 to 14.1% of rainfall. As a result, the average groundwater recharge rate is 3,200 m³/day, with values ranging from 0 to 72,000 m³/day. Recharge primarily occurs during the rainy season. Groundwater also contributes to the Hau River, with a mean flow of 1,300 m³/day during the dry season. Meanwhile, the Hau River contributes approximately 2,240 m³/day to the aquifer system during the rainy season. This study provides a method for quantifying groundwater - surface water interactions on a local scale, which can be valuable for groundwater management in the area.