Model for unsaturated flow above a shallow water-table, applied to a regional sub-surface flow problem
1980
Laat, P.J.M. de (International Inst. for Hydraulic and Environmental Engineering, Delft (Netherlands))
A mathematical model is developed to simulate transient unsaturated flow above a shallow water-table. The unsaturated zone, here extending from just below the phreatic level to soil surface, is schematized into a root zone and a subsoil. In the root zone the gradient of the hydraulic potential is assumed equal to zero. Vertical flow in the subsoil is described by a combination of steady-state situations corresponding to the upper and lower boundary flux, respectively. Transient flow is solved by a sequence of steady-state situations, subject to boundary flux conditions at the soil surface and from below the water table. The solution uses time increments of the order of days and is efficient in terms of computer costs. To verify the model for an actual field situation, it is linked at the upper boundary to a model for evapotranspiration and at the lower boundary to a model for two-dimensional horizontal saturated flow. The resulting quasi three-dimensional model is applied to a field-size flow problem. Results agree closely with observed water-table elevations. The composite model is further used to predict consequences of groundwater extraction
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