Urban groundwater vulnerability assessment using integrated hydrogeophysical methods and GIS for flood-prone tidal zones

Project Abstract

Urban groundwater vulnerability assessment is critical for safeguarding water security in flood-prone tidal zones where salinity intrusion, aquifer deformation, and contamination risks interact with urban land use and climate variability. This study develops an integrated hydrogeophysical-GIS framework to quantify spatial and temporal vulnerability of urban aquifers to tidal influence and anthropogenic stressors. A multi-method data fusion approach combines time-lapse electrical resistivity tomography (ERT), induced polarization (IP), and magnetic resonance sounding (MRS) to characterize subsurface heterogeneity, hydraulic conductivity, and salinity distribution across coastal aquifers. Complementary borehole logs, pumping tests, and geochemical tracers provide validation and enable robust parameterization of a density-dependent flow model that accounts for sea-level rise, extreme precipitation events, and urban recharge pathways. GIS-based vulnerability indicators are constructed from hydrogeophysical outputs, land-use data, population density, wastewater infrastructure, and flood exposure maps to produce a composite Vulnerability Index (VI) at high spatial resolution. The framework is applied to a representative coastal city with mixed carbonate and siliciclastic aquifer systems, delineating zones of low, moderate, and high vulnerability to salinization and over-extraction. Statistical and machine learning techniques (random forest, regression kriging) evaluate the relative importance of drivers and enable predictive mapping under future climate and urban development scenarios. Results indicate that tidal amplitude and aquifer anisotropy dominate salinity intrusion patterns, while preferential recharge through urban drainage channels markedly alters vulnerability hotspots. The integration of hydrogeophysical data with GIS enhances the detection of perched-water bodies, compromised confining layers, and hidden leakage pathways that conventional groundwater models may overlook. Sensitivity analyses reveal that uncertainties in hydraulic conductivity and recharge rates significantly influence VI, underscoring the need for repeated geophysical surveys and continuous monitoring. The study demonstrates improved risk assessment for urban water supply planning, emergency response to saltwater intrusion, and targeted remediation strategies, such as managed aquifer recharge with quality controls and green-grey infrastructural interventions to mitigate flood-induced contamination. Policy implications emphasize the importance of coastal resilience planning, zoning regulations, and integration of subsurface information into municipal groundwater governance. The proposed methodology offers a transferable blueprint for other rapidly urbanizing tidal zones facing complex hydrogeological settings, enabling stakeholders to identify priority areas for protective measures, optimize groundwater abstraction, and enhance sustainable urban water management under changing climatic conditions.

Project Overview

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