Groundwater recharge potential zone mapping for MAR structures in the Cheyyar Basin using grey relational MCDA

Groundwater is a vital resource for agriculture, ecosystems, and people's livelihoods, especially in dry and semi-arid areas with limited surface water. Identifying groundwater recharge potential zones (GWRPZ) and constructing Managed Aquifer Recharge (MAR) structures are critical for long-term water security. This study used a non-explicit weighing technique (i.e., weights implicitly derived from relational analysis rather than directly assigned), such as the Grey Relational Analysis–Multi-Criteria Decision Analysis (GRA–MCDA) framework, to integrate 20 uncorrelated parameters and determine the GWRPZ for the Cheyyar River Basin. The findings show that 27.97% of the Cheyyar River Basin falls into low-to-very-low recharge potential categories, 58.56% of the basin has medium-to-high recharge potential, and an additional 13.47% is classified as very-high recharge potential. The GWRPZ output was validated through spatial correlation with existing well locations, with 53 of 66 wells correctly positioned, yielding a validation score of 0.803. In addition, Groundwater level data (using true positive (TP) and true negative (TN) values) were used to evaluate the model's reliability, yielding an Area Under the Curve-Receiver Operating Characteristic (AUC-ROC) curve score of 0.824. Site-specific MAR structures, such as farm ponds, subsurface dykes, percolation tanks, bench terraces, gully plugs, check dams, and percolation ponds, were recommended based on conditioning principles. These actions are expected to strengthen groundwater resilience, increase agricultural productivity, and stabilize water supplies, directly supporting Sustainable Development Goal (SDG) 6: "Ensure availability and sustainable management of water and sanitation for all," and SDG 15: "Life on Land," by enhancing ecosystem services, conserving soil moisture, and protecting terrestrial habitats.