Exploration of the Effects of Aquifer Storage and Recovery Solutions on the Water Quality and Quantity in a sandy ridge system in Ben Tre, Vietnamese Mekong Delta

Abstract

In the Vietnamese Mekong Delta, climate change, social economic development and a high population density come together and put severe pressure on the delta’s available natural resources and its freshwater availability in particular. Freshwater sources are intensively exploited in order to meet the increasing water demand. This has caused subsidence and saltwater intrusion of both surface and groundwater. Especially in recent years saltwater intrusion is reaching further inland, causing significant damage to crops and is only expected to become more severe in the future. This stresses the need for new sustainable water management strategies. This study will assess the feasibility of such a strategy, an aquifer storage and recovery (ASR) solution, on a shallow phreatic sandy ridge aquifer in the province of Ben Tre in the Vietnamese Mekong Delta and evaluate whether this could provide freshwater security to farmers and secure their agricultural proceeds. As these solutions have shown to be effective in increasing the freshwater lens in the Netherlands on similar geomorphological structures, a pilot study will be done in the Mekong Delta if the solution proves to be effective. The objective of this study was to quantify the impacts of an ASR solution on the freshwater availability and quality at the selected study area in Ben Tre, Mekong Delta, in order to enable a future pilot study. This was done by creating a 3D-variable-density groundwater and coupled solute transport module, using iMOD Water Quality, a feature of iMOD 5.1. Various ASR designs were evaluated, with either vertical or horizontal extraction or infiltration wells. Additionally, the effect of spacing between infiltration wells and the infiltration rate was evaluated. It was shown that the shallow aquifer is sensitive to groundwater extractions and water management practices are required to avoid overexploitation. The study showed that multiple ASR designs can effectively create a water buffer in the dry period. In case of saltwater intrusion of groundwater, horizontal extraction wells are preferable as they prevent extreme chloride concentrations. Note that the concentration of the infiltrated water is crucial to ensure a good water quality, that qualifies for irrigation and drinking purposes. In shallow aquifers with different physical and hydrogeological characteristics ASR solutions were also shown to be effective, which shows the promise of ASR solutions in increasing the water security on a local scale in the Mekong Delta.