Effect of the Capillary Fringe on Steady-State Water Tables in Drained Lands. II: Effect of an Underlying Impermeable Bed

Abstract

A tension-saturated capillary fringe above the water table in drained lands gives rise to lower water tables than would occur in its absence. Results of a conformal mapping solution for the flow from uniform steady rainfall rates on the soil surface to deep drains installed above an impermeable bed when the soil above the drains is wholly tension-saturated show that the effect on the water table is greater the nearer the drain is to the impermeable floor. The effect becomes less with increasing rainfall rate. For the very deep tension-saturated soils assumed in the analysis (that implies a very large negative value for the air-entry pressure for the soil), the results obtained give lower bounds for the water-table heights in real soils with finite air-entry values that lie between the calculated ones and those obtained by theory neglecting a capillary fringe.