Temporal variability of infiltration and roughness coefficients and furrow irrigation performance under different inflow rates

Abstract

Accurate determination of temporal variability in infiltration parameters and Manning’s roughness coefficient is essential for appropriate design of surface irrigation systems to improve irrigation performance and reduce water losses. The objective of this study was to evaluate the effects of temporal variability and different inflow rates on infiltration parameters, Manning’s roughness, and irrigation performance. The field experiments included three inflow rates (1, 1.5 and 2 L/s) and three irrigation events (3rd, 5th and 8th events from 14. Sep. 2016 to 5 Nov. 2016) arranged in three replications at Salman Farsi Agro-Industry Sugarcane fields, located in the southwest of Iran. Also, experimental treatments were conducted in nine furrows with a length of 250 m, the width of 1.83 m and closed-end boundary. The results indicated that there was no significant difference in the Manning’s roughness during the growing season. On the other hand, there were significant reductions of the Manning’s roughness for inflow rates of 1.5 and 2 L/s in comparison with that obtained in inflow rate of 1 L/s. Results also indicated that the cut-off time and infiltrated volume were significantly affected by the temporal variability of infiltration parameters and roughness coefficient. The values of infiltration parameters during the growing season were variable because of various field conditions and sugarcane growth. There were significant differences between the values of parameters of the Kostiakov-Lewis infiltration equation during the growing season. The results showed that changing the inflow rate from 1 to 1.5 and 2 L/sec increased the value of final infiltration rate (f0) in the 5th irrigation event by 6.2% and 39.7% in the 8th irrigation event. The advance and recession times increased during the growing season, in which there was an effective difference in the 8th irrigation event compared to that in the 5th irrigation event. The temporal variability during growing season resulted in a significant reduction in application efficiency (from 74 to 49%), distribution uniformity (from 91 to 80%), and a significant increase in deep percolation (from 25 to 51%). The results showed that when the inflow rate increased from 1 to 1.5 and 2 L/s, the mean values of application efficiency decreased by 3.43 and 24.55%, deep percolation decreased by 27.34 and 34.17% and finally, distribution uniformity increased significantly by 9.7 and 9.3%, respectively.