Inverse estimation of Manning roughness coefficient using WinSRFR model and investigating its variations in different irrigation events

Various methods have been developed to estimate the Manning roughness coefficient, of which the inverse method is widely used. This study aimed to estimate the inverse of Manning roughness coefficient using the WinSRFR model and estimating infiltration parameters of Kostiakov-Lewis equation in furrow irrigation and to investigate their variations in different irrigation events. For this purpose, two inflow discharges (average 0.27 and 0.53 liters per second), two irrigation cycles (5 and 10 days), two fields with different soil texture (E and F) in three irrigation events (first to third) were considered in three replications. Model error in estimating advance and recession time, and volume of infiltrated water was investigated using statistical indices including RE, RMSE and NRMSE. The values of these indices in estimating the advance time in the field E were 0.44%, 0.21 min and 1.11% in the total three irrigation events, respectively. Also, the values of these indices were 1.58%, 5.25 min and 2.78% in the recession time and 0.59%, 5.5 liters and 0.50% in the volume of infiltrated water, respectively. There was less error in estimating the advance and recession time in the field F which showed the excellent accuracy of the inverse estimation method using the WinSRFR model in determining the Manning roughness coefficient. The results also showed that in the field E, the minimum and maximum values of Manning roughness coefficient were estimated as 0.017 and 0.34 and on average 0.075 in the total three irrigation events, respectively. In the field F, the minimum, maximum and the average values of Manning roughness coefficient in three irrigation events were 0.015 and 0.09 and 0.041, respectively.