Water Flow Through Layered Anisotropic Bedded Soil with Subsurface Drains

Results for steady‐state water flow in layered bedded soils with subsurface drains are presented. The soil was assumed to consist of one or more layers bounded below by an impervious barrier and above by a soil surface of uniform slope. Each soil layer was considered water‐saturated and uniformly isotropic or anisotropic within the layer. Anisotropy was defined such that ζ ≠ κ where ζ and κ are the horizontal and vertical hydraulic conductivities, respectively. The finite element method was used in the numerical solution for steady and saturated flow. Although the numerical techniques presented can handle any number of layers, results are only presented for one‐ and two‐layered profiles. The effect of the degree of anisotropy ( R ) and equivalent hydraulic conductivity ( K ) for individual layers (where R = [ζ/κ] 1/2 and K = [ζ κ] 1/2 ) on drain outflow, water seepage along the soil surface, and the relative flow within each layer was investigated. The presence of subsurface drains increased the total flow into the bedded soil surface and decreased (often eliminated) water seepage outflow along the sloping soil surface. The influence of the depth of subsurface drains below the ground surface was dependent upon both K and R of the soil layers. In general, higher K and higher R in the layer containing the subsurface drain resulted in higher drain flows.