Drawdown‐induced consolidation of aquifer systems considering water‐table decline

Abstract

Boundary condition is an important factor in estimating land subsidence induced by groundwater withdrawal. In previous analytical studies, the upper boundaries are commonly assumed to be constant‐head, which could fail to reflect the declines in groundwater table during groundwater pumping. A one‐dimensional (1‐D) consolidation model of aquifer systems due to groundwater drawdown is considered in this study, in which the water‐table decline is taken into account. A mathematical model, which incorporates Neuman's model of unconfined flow into Terzaghi's theory of consolidation, is first presented. The analytical solutions for both hydraulic head drawdown and subsidence are developed in the Laplace domain. A more explicit solution to the elastic, single‐layered model is also derived. The validation of the presented solutions is verified by comparing with existing solutions in degenerated cases. The results show that the presented hydraulic drawdown solutions can be used to describe the water table decline. Moreover, the subsidence solutions are notably different from solutions based on the commonly‐used constant‐head boundary, and these previous models could severely underestimate the subsidence. The influences of specific yield, compressibility of the pore water, hydraulic conductivity, and viscosity of soil skeleton on the water table decline and long‐term deformation are also investigated using the presented solutions.