The Saint-Venant and Richards equation system in surface irrigation: 3. Numerical verification of contact time hypothesis in border irrigation.

The contact time hypothesis is widely used in the simulation of water flow in border irrigation. It implies that water has a predominantly vertical movement in the soil, i.e. the infiltration law is unique along the border In this work contact time hypothesis is verified as a very good approximation to describe water transfer in border irrigation. The verification is done by the internal coupling of Saint-Venant and Richards equations. when the coupling is done by the unidimensional Richards equation, the contact time hypothesis is implicit, but when the bidimensional form of Richards equation is used, the contact time hypothesis is not considered. The assumption of the contact time hypothesis implies the existence of wave fronts that advance slower than those obtained when the hypothesis is not considered. It is verified that the border slope has no effect in the contact time hypothesis for typical slopes used in border irrigation.