An Examination of a Numerical Method for Variably Saturated flow Based on Recent Studies

Abstract

Prediction of ground water movement is very important and critical to forecasting slope failure because many slope failures are triggered by the surcharge of water weight and drop of suction when precipitation infiltrates into soils. It is necessary to consider both saturated and unsaturated flow phases, particularly for sequentially estimating ground water flow to specify the time and location of the failure.
Richards' equation has strong nonlinearity of coefficients. As a result, its numerical analysis tends to be much more difficult than that under moderate conditions, especially with very dry soils or a perched water table. Recently, new methods to solve Richards' equation that focused on diminishing water balance errors and less limitation of time step size were presented (Celia 1990, Pan 1995). In this paper, those new methods are first introduced with explanation of their algorithms specified for balance errors or time step size. Second, based on the fact that both steady and unsteady phases are combined in Richards' equation, the consequent oscillation problem is demonstrated and examined. The algorithm of the oscillation is explained with the analytic method presented in this paper.