TRANSIENT INFILTRATION FROM CAVITIES .1. THEORY

A new method for describing infiltration during filling and draining o f cavities such as, for example, irrigation furrows is presented. The model development decomposes in a first step the two-dimensional (2D) infiltration phenomenon into a series of one-dimensional (1D) processe s, which are described by an extended analytical solution of the 1D Ri chards equation (which incorporates the varying effect of gravity). A special integration over the wetted perimeter of the cavity includes r igorous description of the filling and draining mechanism of the furro w, thus allowing for accurate modeling of infiltration opportunity tim es. Then, two higher levels of approximation are still considered. Mod el version 2 describes with a constant geometry parameter (derived fro m the curvature of the cavity) the impact of the furrow shape on infil tration; and version 3 finally takes into account that the increasing wetted area around the furrow also affects infiltration. All three mod el versions employ only physically based parameters. The method decomp oses the transient infiltration opportunity times; and the varying eff ect of gravity along the wetted perimeter are taken into account. The semianalytical character of the new approach avoids expensive and comp lex numerical solution procedures such as the finite-difference or fin ite-element methods. which recommends its use within a furrow-irrigati on simulation.