Sprinkler Irrigation on Sloping Land: Distribution Characteristics of Droplet Impact Angle and Shear Stress

Abstract

Droplet impact angle and shear stress are important indicators of surface runoff under sprinkler irrigation, and determining the distribution characteristics of these two indicators on sloping land is of great significance for preventing soil surface erosion. Therefore, three slopes (0, 10%, and 20%) and two directions (uphill and downhill) under a Rainbird LF1200 rotary sprinkler were considered in this study. The distribution of droplet impact angles and shear stresses along the radial direction were investigated under various working conditions. The correlations among the droplet impact angle, shear stress, and distance from the sprinkler were also analyzed. These results indicated that the closer to the sprinkler, the larger the droplet impact angle and the smaller the shear stress, and the two indicators gradually decreased and increased with the increase of distance from the sprinkler, respectively. Accordingly, there was a very high potential for soil surface runoff at the spray jet end. It was also observed that the uphill direction generally had a greater impact angle and less shear stress than flat land, while the downhill direction had exactly the opposite result. However, regardless of the direction, an increase in the slope could intensify its effect on the droplet shear stress and impact angle. Therefore, there is an urgent need to focus on the occurrence of surface runoff in soils with larger slopes. In addition, two radial droplet shear stress distribution models were developed, and it was verified that Model 2 had higher accuracy (MAE = 176.6 N m−2, MBE = 32.8 N m−2, and NRMSE = 14.4%) and could be used to predict the average droplet shear stresses at different slopes, directions, and distances from the sprinkler. This study contributes to the soil erosion prevention and the sprinkler irrigation system optimization on sloping land.