Systematic drainage of irrigated soils underlain by an impermeable layer

Abstract

Problems of flow through porous media in which irrigation and drainage are simultaneously taken into account are very often encountered in connection with reclamation projects in arid zones. This article investigates the percolating flow in a soil of finite thickness under conditions of seepage and horizontal closed drainage. The soil is drained by a system of horizontal parallel equidistant circular pipes buried at the same depth. It is assumed that the drains are completely full of water; the pressure head in the soil along the line of contact with the drain is equal to the elevation of its upper point, at which there is no excess pressure. At the surface of the soil the moisture content is constant. This may be the result of a nonuniform irrigation rate distribution. If the irrigation is uniform, the surface layer of soil is nonuniformly moistened: maximum saturation, often supersaturation, occurs midway between the drains, while over the drains the soil is practically dry. The corresponding problem of steady state percolating flow reduces to a boundary-value problem of the theory of analytic functions, by solving which it is possible to determine the irrigation rate distribution needed to ensure uniform humidity of the soil surface.