Spatial and Temporal Variability of Manning's n in Irrigation Furrows

Abstract

Manning's roughness coefficient, n, as a property of space is found to be variable. But its variability is assumed as insignificant in the design of irrigation systems. However, the variability may affect the performance of irrigation, particularly the distribution efficiency. Therefore, an understanding of the statistical behaviour of the variability of n in space and over the crop season may help in improving the models of irrigation system design. In this study, the variability of Manning's roughness coefficient in time and space along the furrow under potato crops was studied. Roughness coefficient estimated along the furrow at different space and in different irrigation events were studied as regionalized variable.· The autocorrelogram did not show any clear trend. Autocorrelation coefficients were around zero for all the lags considered and within the band of significance level. The roughness coefficients estimated at an interval of 10m along the furrow were not serially correlated. The estimated roughness coefficients were normally distributed with mean and standard deviation of 0.0322 and 0.0133, respectively. Hence, roughness coefficient could be treated as stochastic parameter for hydraulic design of furrow irrigation.