The average surface of head gradient in the irregular triangular prism element was proposed to develop a simplified numerical model of solute transport in the irregular groundwater system.The results of the solute mass balance in a triangular prism element were calculated using the hybrid finite element method and the finite difference method basing on the average surface of head gradient.The net lateral solute mass in the control volume to the node was computed by the finite element method and the vertical solute mass to the node by the finite difference method.With the proposed method, the 3-D numerical model was developed and applied to simulate the solute transport in different hypothetic examples.The simulation results of the proposed model agreed well with the analytic solutions.The solute transport model, which has the advantage of saving the computational cost and can be applied to irregular aquifer system,was established on the simplified 3-D groundwater model.Furthermore,upwind finite element scheme and upwind finite difference method were used respectively in the horizontal and vertical directions,which can minimize the numerical oscillation when relatively steep concentration fronts are simulated.
