Infiltration and Roughness Equations for Surface Irrigation: How Form Influences Estimation

Abstract

Some two-dozen methods have been proposed in the literature for estimating aninfiltration function from field measurements. These methods vary in their data requirements andanalytical rigor, however most assume some functional form of the infiltration equations. Also,the Manning n has also been shown to vary with time during an irrigation as the soil is smoothedby the flowing water. Thus estimates of Manning n based on the advance curve may varysubstantially from those based on measured water depths. Inappropriate selection of equationsor parameter values for one (infiltration or roughness) can lead to unrealistic parameter valuesfor the other. This leads to a great deal of uncertainty when such parameters are then used insimulation and design software in order to deduce system behavior with the intent ofimprovement. In this paper, we provide examples that demonstrate the difficulty in theestimation of parameters.