Simulating coefficient of soil moisture content uniformity of sprinkler irrigation systems using a COMSOL-3D model

Water distribution uniformity is important for assessing the hydraulic performance of sprinkler nozzles and designing sprinkler irrigation systems. However, current studies rarely consider the redistribution abilities of sprinkler water in the soil and judge whether a sprinkler system is qualified based only on the coefficient of uniformity on the ground (CU_g), which leads to a serious underestimation of the actual irrigation effect of sprinkler irrigation projects. Hence, this study establishes and validates a COMSOL-3D model to simulate the movement of soil water during sprinkler irrigation. Moreover, the effects of the soil hydraulic and irrigation parameters on the coefficient of soil moisture content uniformity (CU_s) were explored. The results showed that 1) the Nash-Sutcliffe efficiency coefficient (NSE) of the vertical wetting front (VWF) and soil moisture content (SMC) in the two sets of validation experiments was 0.965 and 0.862 and 0.867 and 0.900, respectively. 2) Owing to the differences in soil saturated hydraulic conductivity, after the end of irrigation, the VWF transport rates in vertical direction differed among the three textured soils, with loam exhibiting the highest rate, followed clay loam and silty clay. However, their CU_s increased with increasing water transport time, indicating that the water distribution within the sprinkler-wetted zone became increasingly homogeneous as the sprinkler irrigation water was transported and diffused from the top to bottom in the soil. 3) Dimensional analyses showed that CU_s were strongly influenced by the initial soil moisture content, irrigation time, and water transport time. 4) In Case 4, when CU_g was reduced from 81.9 % to 60 %, CU_s only decreased from 83.2 % to 81.4 % after 48 h of irrigation, indicating that the sprinkler irrigation water had good redistributive ability. This study provides a reference for rationally reducing the CU_s of sprinkler irrigation projects and maximising project investments and planting interest.