THE QUASI-LINEAR APPROXIMATION FOR UNSATURATED POROUS-MEDIA FLOW

This paper gives a review of the quasilinear approximation, an exponential relationship between hydraulic conductivity and moisture potential, and the uses this has been put to since the time of its creation. One of the major attractions of this approximation is that under steady regimes the highly nonlinear Richards equation governing unsaturated flow can be linearized. This simplification has enabled analytic and semianalytic solutions to be found for many unsaturated flow problems. These are reviewed, and the current research areas, in which the quasilinear approximation is being used, are discussed. Copyright 1990 by the American Geophysical Union.