Role of Unsaturated Zone on Aquifer Leakage–Assessed With Tidal Response

Abstract Tidal response analysis is widely used to evaluate aquifer systems, but traditional models that neglect the unsaturated zone often underestimate groundwater leakage. This study develops a new analytical model for tidal analysis that incorporates unsaturated zone effects and explained leakage patterns that traditional models could not resolve. We also found that capillary effects in the unsaturated zone cause aquifers to exhibit larger amplitude ratios and smaller phase shifts, particularly at greater thickness. This effect is like the sealing effect of aquitard, causing traditional models to misjudge leakage. Our results emphasize the need to consider the unsaturated zone in leakage assessment based on tidal methods. The present analytical model offers a novel and more precise approach for leak assessment.