AN INVESTIGATION OF THE RELATIONSHIP BETWEEN PONDED AND CONSTANT FLUX RAINFALL INFILTRATION

The physics of the rainfall infiltration under a constant rainfall flux greater than the hydraulic conductivity at saturation are investigated and compared with those pertaining to the infiltration process under flooding. From the arguments developed theoretically the following conclusions are reached: The moisture profile prevailing at the time the soil surface becomes saturated during the rainfall process (t = T) is identical with the profile which has been developed during flooding at an earlier time at which the infiltration rate is equal to the rainfall flux (t = t(c) < T). The rainfall profile development after T is the same as that of the profile under flooding after T(c), the two profiles having a constant time lag equal to (T - t(c)). The Green and Ampt analysis as has been applied to the constant flux rainfall infiltration presupposes the identity of the profiles mentioned above. In addition to the theoretical arguments, the flow equation was solved numerically for four different soils under the conditions that define the two infiltration processes. The numerical results obtained conform with the theory.