An Analytical Method to Estimate Groundwater Depletion of an Aquitard Due To Variable Drawdowns in Adjacent Aquifers

Abstract

Groundwater is generally overexploited over the world due to the increasing demand for water resources, and it has brought a series of environmental problems, including the decline of groundwater levels, land subsidence (Li et al., 2021;Shi et al., 2007Shi et al., , 2008, and sea level rise (Konikow & Kendy, 2005). A multilayered aquifer system in the sedimentary plain area, such as the Dakota aquifer system in the United States and the Yangtze Delta in China (Guo & Li, 2015;Ye et al., 2016), usually consists of multiple aquifers with alternating aquitards in between (Zhuang et al., 2015). Water stored in aquitards is a significant source of water from pumped aquifers, and aquitards tend to have higher specific storage than confined aquifers (Liu et al., 2022;Zhang, He, et al., 2020). Meanwhile, aquitard storage is difficult to recover and could often be the primary source of groundwater released from the storage of aquifer systems (Shi et al., 2008). Consequently, the accurate calculation of groundwater depletion in aquitards is essential for the effective management of groundwater resources, and it would help to estimate the global transfer of groundwater to surface water (Konikow & Neuzil, 2007).Due to low hydraulic conductivity and nonnegligible specific storage, water release from aquitards and its deformation always lag behind the drawdown in adjacent confined aquifers (Bakr, 2015;Liu et al., 2022;Ye et al., 2016). Zhou et al. (2013) studied the groundwater dynamics and water balance of an aquitard, while the drawdown was a constant amount in an adjacent confined aquifer. The hydraulic head in aquifers lying above or under the aquitard usually decreased with increasing groundwater extraction (Custodio, 2002), Neuman and Gardner (1989) presented convolution integrals for calculating the drawdown in the aquitard under the condition of water table fluctuation. A widely applicable method was proposed to estimate the groundwater depletion of the aquitard in the entire or limited period of exploitation history, especially when the data on drawdown history is sufficient (Li & Zhou, 2015;Li et al., 2017). Konikow and Neuzil (2007) presented a simplified method to estimate the groundwater depletion from the confining layers in response to withdrawals from adjacent aquifers. Alternatively, given the same information, a well-calibrated, numerical simulation model (i.e., three-dimensional