Enhancing groundwater reserves through the managed aquifer recharge (MAR) approach in Lower Kelantan Basin, Kelantan

Abstract

The Lower Kelantan Basin is one of the most important groundwater-dependent regions in Malaysia, where increasing groundwater abstraction, limited effective recharge, and saltwater intrusion pose significant challenges to long-term groundwater sustainability. This study evaluates the potential of Managed Aquifer Recharge (MAR) as a strategy to enhance groundwater reserves and improve water security through an integrated hydrogeological, hydrochemical, isotopic, infiltration, and numerical modelling approach. Groundwater samples from 78 wells were analysed for hydrochemical characteristics, while Carbon-14 (¹⁴C) dating of 13 groundwater samples was used to assess groundwater age and recharge conditions. Infiltration characteristics were evaluated using Double Ring Infiltrometer (DRI) tests at 30 locations, and saltwater intrusion was assessed through surface water surveys along the Lower Kelantan and Pengkalan Datu Rivers. Principal Component Analysis (PCA) and a physically based MIKE SHE model were applied to evaluate groundwater flow dynamics, recharge conditions, and MAR suitability. Hydrochemical results indicate a transition from Ca–HCO3 and Na–HCO3 facies in inland recharge areas to Na–Cl facies in coastal zones, reflecting increasing marine influence along regional groundwater flow paths. Carbon-14 results reveal relatively younger groundwater ages of 410-480 years BP within the intermediate aquifer and older groundwater ages of 547-1,950 years BP within the deeper confined aquifer, indicating contrasting recharge conditions and groundwater renewal rates. Hydraulic conductivity values obtained from DRI testing ranged from 1.81 × 10−6 to 9.48 × 10−4 m/s, demonstrating substantial spatial variability in recharge potential. Despite receiving approximately 3,345 mm of annual rainfall, MIKE SHE simulations indicate that only a small proportion contributes to effective groundwater recharge due to high evapotranspiration and boundary outflow losses. Groundwater abstraction increased from 57 MLD in 1990 to 288 MLD in 2017, increasing pressure on groundwater resources and vulnerability to salinity intrusion. The integrated assessment identified Kubang Kerian, Kenali, Pengkalan Chepa, and Pasir Hor as the most suitable MAR zones due to their permeable sandy alluvial deposits, favourable hydraulic conductivity, relatively younger groundwater, active recharge conditions, and lower salinity influence. The findings demonstrate that MAR represents a viable strategy for enhancing groundwater storage, mitigating saltwater intrusion, and strengthening long-term water security in the Lower Kelantan Basin.