A general approximate method for the groundwater response problem caused by water level variation

The Boussinesq equation (BEQ) can be used to describe groundwater flow through an unconfined aquifer. Based on 1D BEQ we present a general approximate method to predict the water table response in a semi-infinite aquifer system with a vertical or sloping boundary. A decomposition method is adopted by separating the original problem into a linear diffusion equation (DE) and two correction functions. The linear DE satisfies all the initial and boundary conditions, reflecting the basic characteristics of groundwater movement. The correction functions quantitatively measure the errors due to the degeneration from the original BEQ to a linear DE. As the correction functions must be linearized to obtain analytical solution forms, the proposed method is an approximate approach. In the case studies, we apply this method to four different situations of water level variation (i.e., constant, sudden, linear and periodic change) resting on vertical or sloping boundaries. The results are compared against numerical results, field data and other analytical solutions, which demonstrate that the proposed method has a good accuracy and versatility over a wide range of applications. (C) 2015 Elsevier B.V. All rights reserved.