MODELING WATER DISTRIBUTION FOR IRRIGATION MACHINE WITH SMALL SPRAY NOZZLES

A model and computer program were developed to calculate water application depth and uniformity coefficient for small spray nozzles mounted on a center-pivot irrigation system. The program requires two basic inputs. First, the experimental data for the static distribution pattern of the spray nozzle, including collection time, spacing between collection cups, cup opening radius, and volume of water collected in each cup at a specific pressure and height are required. Second, irrigation system inputs including spacing between spray nozzles, radius of distal end tower and moving velocity, distance of spray nozzle from the pivot, move stop cycle time, or cycle time, and percentage of moving time from the cycle time, or percentage of moving time are needed. The outputs are water application depth and uniformity coefficient. Experiments were conducted to validate the simulation for various moving velocities, spacing between spray nozzles, cycle times, and percentages of moving time. Results showed that the uniformity coefficient of water distribution was 98.4% of the predicted coefficient and that by changing cycle time, or percentage of moving time, the uniformity coefficient was improved by as much as 14.2%.