Groundwater augmentation through site-specific surface runoff harvesting in the Western Ghats mountainous watershed, India: insights from geospatial techniques

Groundwater scarcity in the steep-sloped, hard-rock catchments of the Western Ghats, India, results from rapid runoff that restricts natural recharge. The present study evaluates groundwater augmentation through targeted surface runoff harvesting and identifies suitable sites and structures for artificial recharge in the Mannarkad watershed, Kerala. An integrated geospatial approach combining the NRCS-CN hydrological model and multi-criteria GIS analysis was used to estimate surface runoff and delineate groundwater recharge potential zones. Thematic layers, including lithology, geomorphology, slope, soil, rainfall, land use, drainage, and lineament density, were weighted and integrated to identify twenty priority locations for recharge interventions. Runoff potential ranged from less than 3 mm yr⁻1 in the western margins to more than 26 mm yr⁻1 in the central regions. Seasonal groundwater fluctuations showed a post-monsoon rise of up to 2.95 m, confirming effective recharge. Model validation indicated high accuracy, and lineament was identified as the most influential parameter for recharge. Farm ponds, percolation tanks, and recharge pits were recommended for gently sloping areas, while check dams, water absorption trenches, and subsurface dykes were suitable for foothill and fracture-dominated zones. The novelty of this study lies in integrating the NRCS-CN model with GIS-based analysis to identify site-specific groundwater recharge structures in steep-sloped hard-rock terrains. The study demonstrates that properly located runoff harvesting structures enhance aquifer storage, minimize water loss, and strengthen resilience to seasonal water scarcity. The approach can support sustainable watershed management and contribute to achieving Sustainable Development Goal 6 (Clean Water and Sanitation).