Selecting sprinkler packages for center pivots

Center pivots are the primary method of irrigation across the U.S. Great Plains. Center-pivot irrigation is also the fastest growing method of irrigation in the U.S. and around the world. Pivots have the potential to be very efficient and uniform if sprinkler devices are properly selected for local field conditions. New water application devices provide for selection that minimizes runoff and controls droplet sizes to reduce evaporation and drift losses. We present updates to models for computing runoff potential based on characteristics of sprinkler devices and soil textural classes. A dimensionless solution to the Green-Ampt infiltration method for center pivots is presented to better understand factors that influence runoff. That analysis shows that two dimensionless factors are needed to assess the runoff potential. One scaling factor is based on system design, and the second factor is based on irrigation management. An evaporation routine has also been incorporated to estimate potential evaporation losses that may result from utilization of a specific sprinkler design. Modeling runoff and evaporative losses simultaneously allows for comparison of tradeoffs in sprinkler package selection.