Impact of the Intermittency Movement of Center Pivots on Irrigation Uniformity

A computer model was developed to simulate the varying depths of water applied to the ground due to the intermittent movements of a typical center pivot. The stop-go model inputs include the sprinkler application depth, the sprinkler pattern, that pattern's wetted radius, the center pivot's % timer setting, the move cycle time, and the end tower maximum travel speed. The model outputs were the depth of application in the pivot's movement direction, the distribution uniformity (DU), and the coefficient of uniformity (CU). The results revealed that the pivot circular application uniformity is mostly a function of the move distance as a percent of the sprinklers' wetted radius. This, in turn, is a function of the percent timer setting, the cycle time, and the end tower travel speed. Due to this, the high-speed center pivots had corresponding lower application uniformities compared to low-speed machines, and sprinklers with larger wetted radii resulted in better uniformity. Shortening the cycle time also resulted in higher uniformity coefficients. Based on these results, it is recommended that the run time be set based on the pivot end-tower's travel speed and sprinkler wetted radius, such that the end tower move distance is equivalent to the sprinkler wetted radius. This will reduce wear to the tower motors due to the on-off cycling, especially for slow travel settings and for sprinklers with larger wetted radii. The ponding depths at different percent of the move distance, for the potential runoff, were estimated, which were set to be equivalent to the wetted radius.