Development of a new method for determination of infiltration coefficients in furrow irrigation with natural non-uniformity of slope

In this study, a new method was developed to calculate the infiltration coefficients in furrow irrigation with natural non-uniformity of longitudinal slope. For this purpose, 12 usual tilled furrows with 42 m length and 60 cm width were selected. Then, five irrigation events were carried out and the advance-recession and inflow-outflow data were collected. The parameters of the infiltration equation in power-polynomial form (Kostiakov–Lewis) were calculated using the volume-balance (VB) method and based on a power model as advance equation. The non-uniform longitudinal slope in furrows was purposefully made, so that the advance function should not to follow a usual power function, and the power of function to be more than one in some cases. Besides, in some irrigation events, the negative infiltration equation was obtained. Accordingly, from analysis of VB equation components, several modifications were incorporated in procedure of parameter estimation. Some of these modifications include fitting a quadratic function for advance data and calculating the flow cross-sectional area from maximum surface storage value. Volume of infiltrated water was calculated using this method in each irrigation, and compared with the measured volume based on the inflow and outflow hydrographs as a control. The results showed that using the presented method, the average error in computed infiltrated volumes was reduced to about 4%, which validates the application of the new method.