Enhancing groundwater recharge in Malta : proposing a ground permeability model for infiltration boreholes in Maltese limestone

Abstract

Malta faces ongoing challenges in securing potable water due to its geographical and climatic limitations. Historically, the Maltese relied on groundwater and rainwater storage, but modern reliance on aquifer pumping has led to over-extraction, particularly from the mean sea level aquifer. Despite the high risks observed on water resources in Malta, the rate of urban development has contributed to soil-sealing effects without the implementation of any mitigation measures, resulting in an increase in flash flooding and a decline in permeable areas for groundwater recharge. This dissertation examines past and present water conservation practices and proposes infiltration boreholes for managed aquifer recharge (MAR) in Malta’s limestone strata. By analysing local ground conditions, the study aims to estimate recharge rates through a simplified dry well model and evaluate the feasibility of MAR as part of a broader and more streamlined aquifer recharge strategy. A parametric model was developed to predict recharge rates, demonstrating that water head loss, flow velocity, and volumetric flowrate in emptying infiltration boreholes decrease over time. The model also highlights the significant impact of fissure concentration and infill material on flowrate estimations, as well as the differences between primary and secondary permeability. The model was created to map directly onto existing local drilling record data, in order to facilitate direct input of rock quality designation (RQD) values and borehole dimensions and to hasten the estimation and design process of local MAR projects. Further testing is required to refine the model and increase confidence in site-specific predictions, especially regarding flow resistance factors within fissures.