Hydrodynamic evaluation of irrigation efficiency through raingun sprinkling

High pressure sprinkling in overlapping wetting circle geometry was attempted with rain-gun sprinklers. Discharges and radii of throw in tandem with frictional head losses along the pressurized flow grid were calibrated for different operating pressure heads. For a square grid overlapping of four wetting circles, the total depth of water received in the overlapped zone was mathematically modeled. The deviations of on-field observations using catch cans with a grid square of 5 x 5 m were analyzed and the water distribution uniformity was computed. For this impulse of water distribution uniformity, the responses in terms of the sub-soil moisture storage, application and distribution efficiencies were determined. Rain-gun sprinkling has been found to be relatively more efficient (CU >72%) than the conventional sprinkling for given soil, crop and field conditions. The performance evaluation of rain-gun system showed that the water was applied with moderate uniformity with a low pressure (1.5 kg cm²) pump. The results showed that the uniformity of application was increased by around 7.3% and 6.87% by giving 50% overlapping by another full-circle and half-circle raingun sprinkler, respectively. The soil moisture distribution efficiency was found to be around 81% within the effective root zone after irrigation. The study also suggested that in case the rain-gun irrigation system was operated with low HP pumping system, efficient water application and uniformity could be achieved only with sufficient overlapping network.