Groundwater and River Interaction Impact to Aquifer System in Saigon River Basin, Vietnam

Abstract

Since the 1990s, under the pressure of socio-economic growth in the Ho Chi Minh City and nearby provinces, the heavy-extraction of groundwater of this area has dramatically increased to meet high water demand for domestic and industrial purposes. Although the groundwater – Saigon River interaction significantly contributes to groundwater reserves, researchers have been less attentive to fully describe and understand the river recharge. This study attempts to explore the impact of groundwater-river interaction to aquifer system due to pumping increase via field seepage and (O18, H2) isotopic measurements in the Saigon River Basin, South East of Vietnam. The analysis showed that river bed conductance at 0 km, 30 km, 60 km, 80 km, and 120 km were 4.5 m2/day/m, 4.2 m2/day/m, 2.5 m2/day/m, 1.7 m2/day/m, and 0.25 m2/day/m respectively. The riverbed conductance relies on the sand percentage of sediment. The composition δO18 in groundwater, river, and precipitation indicates that river recharge to groundwater exists mainly in the lower part of the basin. In contrast to downstream, the composition of δO18 was signified that the river primarily gains water from groundwater upstream. Under pressure of developing economies, the groundwater pumping in the Saigon river basin increased from 175,000 m3/day in 1995 to 880,000 m3/day in 2017. As a consequence of the increased pumping rate, the groundwater discharge to the river decreases from 1.6 to 0.7 times of groundwater pumping in upstream, while the amount of Saigon river recharge increases by 33% to 50% of the total groundwater pumping downstream. Under the exceedance pumping rate, the aquifers in the Saigon River Basin release less water to the Saigon river and it tends to gain more water through the river - groundwater interaction process. Therefore, groundwater management in downstream aquifers needs better joint planning with surface water development plans, particularly for surface water supply utilities which still struggle to satisfy the water demand of the development plan.