A mathematic time dependent boundary model for flow to a well in an unconfined aquifer

In this paper, hydrodynamic lag in ground water is studied on the basis of achievements of principles and technical knowledge relating to flow in porous medium. Due to hydro dynamic lag character in phreatic aquifer, the ground water flow field can be divided into perturbation part and no perturbation part, that illustrates the boundary of phreatic aquifer is changeable. The degrees that the change of impervious boundary exerts influence over calculation of isolated well model in phreatic aquifer is analyzed. Thus, a physical model with time-dependent boundary in phreatic aquifer is established. The model with time dependent boundary can be superposition of a series of isolated well model with variable impervious boundary. Applied superposition principle, analytical solution of the model is derived.