Steady-state groundwater flow model with variable hydraulic conductivity

Classical aquifer test models assume an isotropic and homogenous medium with Darcian flow as an ideal case. Deviations from type curves indicate the heterogeneity of the aquifer. There are heterogeneities even at small scales. There are also systematic variations which are not considered by type curves. For instance, due to the groundwater movement during the well-development phase, the hydraulic conductivity tends to decrease with radial distance from the well. For practical representation of such a systematic variation, a linear hydraulic conductivity decrease is adopted and the relevant type curve expressions are derived. These expressions are checked against the classical constant hydraulic conductivity solutions in the literature. Derived type curves are employed for the identification of aquifer parameters, namely transmissivity and the radial hydraulic conductivity variation parameters. The type curve expression derived transforms into the classical Thiem expression when the aquifer hydraulic conductivity is considered as constant. It is observed that classical steady-state flow with constant hydraulic conductivity underestimates the transmissivity by 10%.