Comparative Analysis of Groundwater Recharge Estimation Using Geophysical Methods in Urban and Rural Areas

Thesis Abstract

Groundwater recharge estimation is vital for sustainable water resource management, particularly given the increasing pressures from urbanization and climate variability. However, the methodologies employed often vary significantly between urban and rural contexts, resulting in discrepancies that hinder integrated water resource planning. This study aims to conduct a comparative analysis of groundwater recharge estimation using geophysical methods in urban and rural areas, with an emphasis on evaluating the efficacy, accuracy, and practical applicability of various geophysical techniques within these distinct settings. The specific objectives include 1) to identify and compare the most effective geophysical methods for recharge estimation in urban and rural environments; 2) to assess the influence of land use and subsurface heterogeneity on geophysical measurement accuracy; 3) to develop an empirical model correlating geophysical parameters with recharge rates; and 4) to recommend context-specific best practices for groundwater recharge assessment. The research adopts a cross-sectional, comparative research design grounded in the pragmatic paradigm, integrating qualitative and quantitative data. The study population comprises soil and subsurface samples from two representative locations—one urban and one rural area—each with a population of approximately 15,000 residents, selected based on hydrogeological homogeneity and accessibility. A stratified random sampling technique was employed to select 30 boreholes within each environment, from which data were obtained. Data collection instruments included electrical resistivity tomography (ERT), ground-penetrating radar (GPR), and vertical electrical sounding (VES) for geophysical measurements, complemented by soil moisture content and rainfall data obtained from installed sensors and meteorological stations. To ensure validity and reliability, calibration of geophysical instruments was performed prior to data collection, and measurements were cross-validated using groundwater level observations and isotope analyses. Data analysis involved descriptive statistics to characterize the subsurface features and recharge factors, and inferential statistics including regression analysis and two-way ANOVA to examine differences between urban and rural environments. A multivariate analytical framework was employed to develop a predictive model of recharge based on geophysical parameters. The research also incorporated the application of the geological theory of conductive heterogeneity and the hydrological theory of recharge processes to interpret the geophysical data within the respective contexts. Expected findings indicate significant differences in the accuracy and effectiveness of geophysical methods between urban and rural environments, with some techniques demonstrating higher reliability in rural settings due to less anthropogenic interference. The analysis is anticipated to reveal that land use patterns, subsurface heterogeneity, and human activities significantly affect geophysical measurement outcomes and recharge estimates. The empirical model developed is expected to demonstrate a high correlation (R² > 0.85) between geophysical parameters and recharge rates, providing a robust tool for practical application. This research contributes novel insights into the context-dependent applicability of geophysical methods in groundwater recharge estimation, filling a critical gap in comparative hydrogeological methodologies. It advances the field by providing a framework for selecting appropriate geophysical techniques based on environmental characteristics, thus aiding policymakers and water managers in making informed decisions. The study concludes with tailored recommendations for adopting specific geophysical approaches in urban versus rural contexts and suggests avenues for further research into integrating remote sensing data and hydrogeological modeling for enhanced recharge assessment accuracy. Overall, the findings underscore the importance of environmental context considerations in geophysical hydrogeology and offer practical pathways for improving groundwater management practices globally.