Cylindrically Confined Flows of Water from a Point Source and to a Sink, above a Water Table

摘要

A quasi-linear form of Richards' equation, which assumes exponential dependence of the hydraulic conductivity on the pressure head and depth, was used to analyze the flows from a point source and to a point sink in a cylindrically confined soil domain overlying a shallow groundwater table (WT). The evaporation flux at the surface was taken to be proportional to the matric flux potential (MFP). Analytical solutions for the time-dependent and steady-state problems were obtained by using integral transforms. The general solution for a point source in a finite-length cylinder takes the form of double series, which contains the inverse of the finite Hankel transform in the radial direction coupled with the inverse of the generalized Fourier transform in the vertical direction. Numerical evaluation of this solution is straightforward but time consuming for both time-dependent and steadystate cases. An alternative solution for a steady point source that involves only the Hankel inverse transform was found to be more practicable. Steady flows from a surface point source toward a WT and from a WT toward a subsurface sink were analyzed by mapping the distributions of the pressure head and the MFP, together with the streamlines. The sink was simulated by a suction zone of prescribed radius whose strength was evaluated from the condition that MFP equals zero at a reference point at either the bottom or the top of the suction zone. Particular attention was paid to the choice of locations of the reference point for evaluating the sink strength, for which the solution for the sink remains physically relevant irrespective of whether or not the surface loses water by evaporation.