Second-order shallow flow equation for anisotropic aquifers

•We include anisotropy in the new development of the second-order theory.•The bank-storage problem is used as test case.•A new analytical solution to the second-order theory is presented. Transient unconfined ground-water flow is described using the well-known Boussinesq equation, in which the Dupuit assumptions are implicit. When these assumptions fail, one must recur to the next level of approximation, which is the second-order theory for shallow flow in porous media, developed by Dagan (1967) for isotropic aquifers. When the soil is highly anisotropic Dagan’s second-order theory can become invalid. Here we present the generalized second order theory that account for anisotropy. An analytical solution for the second-order theory with anisotropy is presented for the linearized equation that is used to illustrate this effect on the bank storage problem.