Recharge from an ephemeral stream following wetting front arrival to water table

Abstract

After the infiltration wetting front from a river bed of an ephemeral stream in flood reaches the shallow water table, the rate of recharge, which is also that of infiltration, is affected by the development of a groundwater mound. The effect is practically immediate if the water content behind the wetting front is close to saturation. An approximate analytical solution is developed in that case, which predicts the time dependence of the recharge rate. Comparison with experimental results in the laboratory shows that the solution is excellent in spite of the assumptions necessary in the derivations. As long as the ratio of river width over depth to water table exceeds 2 and as long as the ratio of initial saturated thickness over depth to the water table exceeds 2.5, the analytical solution is essentially exact. Under most field conditions these ratios are largely exceeded. Consequently, the predictive equation for the time dependence of the recharge is both quite simple to use and adequately accurate for field applications.