Evaluating surface water quality dynamics in the Coastal Delta of Tamil Nadu through an integrated irrigation hazard and GIS approach

Coastal deltaic regions of Tamil Nadu are increasingly affected by salinization, intensive irrigation, and land-use transformation, yet existing studies often examine water quality or biodiversity independently, limiting their applicability for integrated resource management. Addressing this gap, the present study provides a spatially integrated assessment linking surface water irrigation suitability, hydrochemical controls, and broader land-use and ecological contexts across the coastal districts of Thiruvarur, Thanjavur, and Nagapattinam, Tamil Nadu. The study evaluates surface water quality for irrigation, identifies dominant hydrochemical processes and seasonal variability, and examines their implications for environmental sustainability. Field-based surface water sampling was combined with remote sensing, GIS techniques, and multivariate statistical analyses. Irrigation suitability was assessed using the Irrigation Water Quality Index (IWQI) along with salinity, sodicity, and magnesium hazard indices, while Pearson correlation and factor analysis were employed to identify the key drivers of water quality degradation. The results indicate that 48% of samples fall under moderate to severe irrigation restrictions, primarily due to elevated magnesium and salinity hazards, whereas sodicity remains largely within acceptable limits. GIS-based spatial analysis identified highly vulnerable coastal tracts, delineated as ‘Red zones’, while multivariate results highlight agricultural intensification, salinization, and excessive groundwater extraction as major anthropogenic controls. Overall, the findings provide actionable insights for zone-specific irrigation management, groundwater regulation, and sustainable coastal resource planning, with indirect relevance to biodiversity conservation, contributing to the achievement of SDGs 6, 13, and 15.