EFFECT OF WIND SPEED AND PRESSURE ON LINEAR MOVE IRRIGATION SYSTEM UNIFORMITY

Abstract

Use of center pivot and linear move sprinkler irrigation systems is becoming popular in the Southeastern United States. As these systems are used to irrigate increasing acreage, quantitative data are needed on sprinkler performance under local conditions. Two types of low pressure sprinkler nozzles were tested under field conditions, stationary grooved plate (LDN) and off-center wobbling diffuser sprinklers (IWOB). Replicated uniformity measurements were conducted along the axis of a linear move irrigation system at low (<1.7 m/s), medium (3.3-3.9 m/s), and high (5.0-6.6 m/s) wind speeds and at two pressure levels of at least 200 kPa, which was in excess of the pressure regulator discharge pressure and less than 97 kPa, a pressure below nominal regulator discharge pressure. Also, the normal probability distribution was investigated to determine how well it represented the sprinkler field data. The IWOB sprinklers coefficient of uniformity (CU) was consistently 10% to 16% higher than the LDN sprinklers over all conditions and ranged from 87% to 93% and 70% to 85%, respectively. The coefficient of uniformity of the LDN sprinklers was significantly improved at higher wind speeds (5.0-6.6 m/s) under low pressure (<97 kPa) operation from 70% to 85%, while other sprinkler/pressure combinations were not affected by wind speed. It was hypothesized that this improvement was due to the formation of larger drops falling in a more random pattern due to inadequate pressure. Finally, the IWOB sprinklers produced a more uniform application of water compared to the LDN sprinklers under all of the testing conditions in this project and the normal distribution adequately represented the field data except for LDN sprinklers at <97 kPa.