Comparative Assessment of Urban Groundwater Recharge in Adjacent Basins

Thesis Abstract

Groundwater resources in rapidly expanding urban settings face increasing risk from altered recharge dynamics, urbanization-induced impervious surfaces, and heterogeneous subsurface conditions, prompting a need to quantify and compare recharge pathways across adjacent basins. This study aims to assess and contrast urban groundwater recharge in two neighboring basins to inform sustainable aquifer management under expanding metropolitan pressures. Specific objectives are to (i) quantify natural and artificial recharge components using hydrogeochemical tracers, (ii) evaluate spatial and temporal variability in recharge rates through isotopic methods and water balance modeling, (iii) identify controlling hydrogeological and land-use factors via multivariate analysis, and (iv) propose basin-specific management interventions grounded in comparative evidence. The research adopts a comparative cross-sectional design, focusing on two hydraulically connected basins within a metropolitan region with contrasting urban morphology. The population comprises groundwater wells (n ? 60 per basin) and key hydrological monitoring stations distributed to capture vertical and lateral recharge processes. A stratified random sampling approach selects 40 wells for tracer sampling and 12 monitoring stations for hydrometric data. Data collection integrates hydrogeochemical analyses (major ions, stable isotopes 18O and 2H, and dissolved inorganic carbon), environmental tracers (tritium for young groundwater, chlorofluorocarbons where available), groundwater level measurements, soil moisture and rainfall data, and land-use inventories derived from high-resolution remote sensing. Instrument validity is ensured through calibration against certified standards and inter-laboratory checks, while reliability is enhanced by duplicate sampling and quarterly data collection over two hydrological years. Analytical techniques include end-member mixing analysis to partition recharge sources, Nickell-type regression for recharge-rate estimation, and linear and multiple regression models to link recharge to hydrogeological and anthropogenic factors. A Catchment-Scale Water Balance Model (CS-WBM) calibrated with observed recharge components and a Bayesian hierarchical framework will be employed to compare uncertainty bounds between basins. The theoretical underpinning draws on the theory of groundwater recharge processes and the urban hydrogeology framework, with key reference to the Cone of Depression concept and the Environmental Isotope Approach for tracing recharge, complemented by Sustainable Urban Drainage Systems (SUDS) theory to interpret artificial recharge signals. Expected findings indicate distinct recharge signatures between basins driven by differences in impervious surface fraction, green space distribution, aquifer transmissivity, and irrigation practices. It is anticipated that Basin A exhibits higher natural recharge rates via preferential recharge through unpaved infiltrative zones and urban gardens, whereas Basin B shows enhanced artificial recharge under extensive SUDS implementation but reduced natural recharge due to severe stormwater routing. Statistical outputs are expected to reveal significant correlations (p < 0.05) between recharge components and land-use indices, aquifer thickness, and rainfall interception by building storage. The study contributes to knowledge by delivering a transferable, evidence-based comparative framework for urban recharge assessment, integrating isotopic, hydrochemical, and hydrological approaches to quantify the relative roles of natural and anthropogenic recharge. The findings will refine groundwater management in urban basins through basin-specific recommendations on recharge enhancement or protection, groundwater withdrawal planning, and land-use zoning. The conclusion emphasizes the need for integrated urban water planning that harmonizes recharge optimization with water security, proposing policy interventions such as harmonized infiltration zoning, targeted green infrastructure investments, and routine tracer-based monitoring to sustain urban groundwater resources. Policy implications include incorporating basin-specific recharge benchmarks into municipal groundwater budgets, establishing joint basin management agreements, and guiding future urban expansion with respect to recharge preservation.