A CONSERVATIVE 2D SUBSURFACE FLOW MODEL FOR CURVILINEAR COORDINATE SYSTEMS

A mass conservative finite difference scheme to describe 2D unsaturate d/saturated subsurface flow is developed. The development takes into a ccount important findings of Celia et al. (Water Resour. Res., 26(7) ( 1990) 1483-96) and extends their mass conservative 1D approach to two space dimensions. Moreover, using the theory of metric coefficients, t he numerical model is not restricted to cartesian coordinates but is g enerally formulated for arbitrary orthogonal coordinate systems, thus accounting for curved boundaries of a computational domain. For flux b oundary conditions convenient formulae avoid the cumbersome use of ima ginary points outside the computational domain without reducing the or der of magnitude of the approximation error. A flexible iteration stra tegy caters, on the one hand, for accuracy and stability when simulati ng sharp wet fronts and, on the other hand, for an economical calculat ion. The model was compared with the outcome of a laboratory experimen t which investigated the transient development of the infiltration pat tern in initially dry sand as a result of filling a circular cavity.