An analytical solution for infiltration in soils with a shallow water table: application to gravity irrigation

Abstract

An analytical solution of the Richards equation is deduced using Green and Ampt hypotheses to describe the infiltration in soils with a shallow water table. A linear initial moisture profile is assumed, so that the minimum value is at the soil surface and the maximum value at the water table level. A linear variation of the driver pressure is accepted, it is maximum at the soil surface and zero at the water table level. The Green and Ampt equation is deduced from the solution when the water table depth tends to infinite. The solution is compared with a numerical solution for linear initial moisture profile and for an initial hydrostatic pressure distribution, with good results in both cases. In the Lewis and Milne model, the infiltration solution is introduced to describe three tests of advance phase in border irrigation of the rice culture at La Chontalpa, Tabasco, Mexico, to different water table depths. In the first one the parameters regarding the infiltration and the flow resistance law at the soil surface are calibrated and in the other two tests, the prediction of the advance front evolution is carried out; in the three tests, the advance theoretical curves are very near to the experimental curves. The established infiltration solution can be used designing border irrigation in soils with shallow water table like agricultural zones under irrigation or with slow drainage.