Computing aquitard depletion, which is often overlooked, is of great
significance for the assessment of groundwater resources and land
subsidence. The issue is viewed as troublesome because of the additional
computational burden, the poorly known hydrogeological parameters of the
aquitard, and the lack of drawdown history in pumped aquifers. In this
study, an analytical solution is derived to describe the drawdown
variation in a nonlinear-consolidated aquitard under the condition of
variable drawdowns in adjacent aquifers. Based on the analytical
solution, we study the characteristics of groundwater dynamics and water
balance under the conditions of linearly increasing drawdown of aquifers
in adjacent aquifers. In addition, we put forward a method to calculate
the depletion and hydrogeological parameters of an aquitard
corresponding to variable drawdowns in adjacent aquifers, applicable
even when historical drawdown data are lacking. The accuracy of the
method is generally very good, but results improve when the drawdown
history of pumped aquifers is divided into more periods for estimation.
Under the condition of linear drawdown in adjacent aquifers, groundwater
depletion and maximum water release rate of the aquitard increases with
increasing compression index, coefficient of consolidation, aquitard
thickness, rate of drawdown change in the adjacent aquifer, while
decreasing with initial void ratio, and initial effective stress. The
proposed approach is demonstrated at a field site in Shanghai City of
China, and it would help for the effective management of groundwater
resources and estimation of the global transfer from groundwater to
surface water.