Horizontal soil-water intake through a thin zone of reduced permeability

One-dimensional, horizontal soil-water absorption through a thin zone of constant nonzero hydraulic resistance is examined theoretically and experimentally. Mathematically, this involves a numerical solution, as well as a similarity reduction of the problem for early to intermediate times. The flow equations are transformed by introducing a dimensionless parameter, which enables the solution for any value of thin-zone resistance to be obtained from the solution for a given known thin-zone resistance. At the inlet boundary between the thin zone and the soil column, the soil-water content increases with time to approach the saturated value. The cumulative absorption of water by the soil column increases more than proportionally with the square root of time for early and intermediate times, and approaches a square-root-of-time proportionality at large times. For both the soil-water content at the inlet boundary and the cumulative water absorption by the soil column, simple expressions arise from the similarity-reduction analysis, which is based on specific functional forms of the soil-water diffusivity and suction head. For early to intermediate times of flow, the similarity-reduction analysis describes adequately the calculated numerical-solution flow data for Yolo soil, as well as the measurements obtained experimentally on Salkum silty clay loam.