Controlling sprinkler rotation speed to optimize water distribution uniformity of travelling rain guns

Big travelling rain guns irrigate the field according to a typical bell-shaped pattern having a potentially negative effect on distribution uniformity, irrigation efficiency and working capacity. Field experiences demonstrate that old travelling sprinklers do not allow good distribution of water, unless large wetted areas overlap. Recent big sprinkler models take advantage of improved hydraulic and mechanical characteristics, and under normal field operations, overlapping of wetted areas is about 15% of sprinkler diameter (SD). Irrigation performance of big travelling rain guns can be improved by flattening the water distribution curve. This condition can be achieved through accelerating the sprinkler rotation speed while irrigating the central sector of the wetted area. A mechanical device, named Uniform, was designed and manufactured to this end. A big rain gun was equipped with the device, and compared to an identical rain gun (Explorer), according to the same nozzle/pressure setting resulting in 56 m sprinkler radius. A field test under no wind conditions was carried out in two experimental fields, bare and flat, arranged in parallel according to ISO 8224-1 n. 584, in order to assess the effectiveness of the device both in absolute and comparative terms, according to Christiansen's uniformity coefficient, CU, and low-quarter distribution uniformity coefficient, DUIq. Under test conditions, when adjacent travel lanes of the cart were spaced from about 75% to 90% of sprinkler diameter, average DUIq of Uniform ranged from 0.88 to 0.80, and CU varied from 92% to 88%. In the same spacing interval, DUIq of Explorer ranged from 0.86 to 0.70, and CU from 90% to 82%. The highest average DUIq and CU values for Uniform occurred when adjacent travel lanes were around 85% of SD, for Explorer when spacing was 80% of SD. Acceptable values of DUIq and CU over the irrigation strip were allowed by Uniform for travel lanes spacing about 90% and 95% of SD, respectively. The same values decrease to 88% and 92% of SD without the rotation speed controller. Compared to Explorer, we found that a 5% wider area can be irrigated by Uniform when given the same uniformity, and potential water saving due to uniformity is about 15%. It should be noted that quite a simple mechanical device enabled appreciable potential water saving, proving that irrigation performance can benefit from relatively small investments.