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Aquifer storage and abstraction impacts
Published in Ian Acworth, Investigating Groundwater, 2019
Acworth et al. (2016a) demonstrated that it was possible to calculate the BE in the frequency domain where the impact of the atmospheric tide as 2 cpd (S2) was very constant. A simple ratio of the amplitude of the groundwater response at 2 cpd to the atmospheric pressure response, expressed in the same units and at the same frequency, is an approximation to BE (Acworth and Brain, 2008). Further work (Acworth et al., 2015a) demonstrated that the BE values were a slight underestimate of BE because there was another factor involved. The groundwater level response to atmospheric pressure at 2 cpd is contaminated by a response to earth tides at the same frequency. The earth tide acts to diminish the response to atmospheric pressure and requires backing out before the ratio is calculated to estimate BE.
Determining the hydraulic properties of coastal aquifer systems using groundwater response to tidal fluctuations: applicability and limitations
Published in Coastal Engineering Journal, 2020
Ling Yang, Ming Zhang, Yonghong Hao, Tongke Wang, Zhixue Zhao
We developed an analytical solution for a coastal aquifer system that consists of a leaky confined aquifer on an impermeable ocean-bed overlapped with a semi-impermeable aquitard, and then an unconfined aquifer on the top, imposed by dual-frequency tidal fluctuations. The solutions for a perfectly confined aquifer and single-frequency tidal fluctuations can be considered as special cases of the newly developed, generalized solution. The transport of ocean tides through a leaky confined aquifer depends on both the hydraulic diffusivity of the aquifer and leakage of semi-impermeable aquitard overlapped on it. Ocean tides could only transport to a limited distance toward inland if the hydraulic diffusivity is low and/or the leakage is large. Cautions should be excised that both earth tides and changes in local atmospheric pressure may induce similar tidal fluctuations in the hydraulic head within an inland monitoring well. Both the hydraulic diffusivity and leakage can be identified from the monitored, time-depended fluctuations of hydraulic head detected with reliable accuracies. By incorporating the use of aquifer thickness that can be determined independently from observation of core materials during drilling of a monitoring well, both the transmissivity and storage coefficient of a perfectly confined aquifer or a confined aquifer with small leakage can be simultaneously estimated. The findings obtained from this study may provide a better understanding of using ocean tides for determining the hydraulic properties of coastal aquifer systems and a practical example for examining the applicability and/or limitations of the tidal method.