Subsurface drainage in a soil overlying an impermeable layer

Abstract

Subsurface drainage in a homogeneous saturated soil has been thoroughly studied and has been analyzed by numerical techniques or by the use of the mean soil water diffusivity (Gardner 1962). When permeable layers overlie an impermeable layer, subsurface drainage in the upper layers after saturation is far different from the drainage in homogeneous soils. In such a case, the pressure head in the upper layers becomes close to the hydrostatic pressure, because the lower impermeable layer impedes the drainage of the upper layers. Measurements of pressure head and hydraulic conductivity in the lower deep layers, however are not easy in comparison with those in the shallow layers. Under these conditions, it is convenient to analyze the subsurface drainage in the upper layers using models. In this paper, we present simple drainage models which are based on data of the curve of the soil water characteristics and the changes in the depth of the water table with time. These models described adequately subsurface drainage in the absence of determination of the hydraulic properties of the lower impermeable layer. © Taylor & Francis Group, LLC.