Investigation of the accuracy of some models to estimate of wind and evaporation losses in fixed head sprinkle irrigation system

Due to widely used sprinkle irrigation systems, it is necessary to prepare a develop model to estimate evaporation and wind Drift losses. Parameters and many factors are effective the amount of losses due to evaporation and wind in the sprinkle irrigation systems. These factors can generally be divided into two categories of climatic parameters and the system. The purpose of this study is the assessment of proposed equations by some former researchers (Montero et al., Trimmer, Frost and Schwalon, Keller and Bliesner) to estimate of evaporation and wind drift losses of sprinkle irrigation systems in the Sanandaj city. The standards ISO 7749-1 and ISIRI 8995-3 and single sprinkler method have been taken to determine evaporation and wind drift losses for 3 sprinklers (AMBO, ZM22 &.ZK30). The nozzle diameter of sprinklers were ZM22 (10, 3.5), AMBO (10, 7) and a sprinkler ZK30 (8, 3.5) mm. To supply sprinkler operating pressure was used of a device dry horizontal electro pump. The main pipe was of polyethylene with an outside diameter of 160 mm. The butterfly valve in the bypass pipe was used to adjust of the pressure of model. A Sub main polyethylene pipe was used with a diameter of 50 mm and a length of approximately 120 m to conveyance water to the sprinkler. In this study was considered riser height 165 cm. Sprinkler pressure was measured at the point of the riser. This point was lower than the point of changing of riser diameter. This distance must be at least 10 times the diameter of the riser. For measure discharge of sprinkler was used volumetric.Then the test zone was an area of 60 × 60 square meters networking. The test zone was networked by using plastic meter and wooden sticks (3m×3m), and water collecting buckets each with 90 mm height and 80 mm of internal diameter were installed. The minimum of test time was 1 hour. This investigation is performed to assess effect of different intensities of wind and pressure amount at 4 pressure of system (3, 3.5, 4 and 4.5 Bar), at 2 types of wind velocities (0-1.8 calm wind, 1.8-4.4 average wind) were applied.On-site testing wind speed with a handheld anemometer at a height of about 2 meters were measured and temperature and relative humidity by TESTO 615 device.
The results of linear regression showed that the results of methods of Montero et al.(2000) and Keller and Bliesner (1990) per 3 sprinklers ZM22, AMBO and ZK30 had significantly different from the actual amounts of losses due to evaporation and wind.Also computational results of Frost and Schwalon had significantly different in both sprinklers of Ambo and ZK30 at probability 5 and 1 percent respectively and has not significantly different in ZM 22.In both ZM22 and ZK30 sprinklers computational result of Trimmer(1990) method are not significantly different with actual result of losses due evaporation and wind but in Ambo sprinkler was significantly difference at probability level 1 percent. In three studied sprinkler Montero et al.(2000) equation showed amount of losses more than actual losses but Keller and Bliesner (1990) method was less than actual losses. Also result of Frost and schwalon (1955) in both of Ambo and ZK30 sprinkler and Trimmer method in the Ambo sprinkler are less than actual amounts. Also, based on NRMSE, the accuracy of all models is weak to estimate losses due to evaporation and wind in all three studied sprinkler. Accuracy of the results obtained from a trimmer (1987) for ZK30 sprinkler was at the border of moderate to weak.
The results of both methods to evaluate of the accuracy models have shown that the used models for estimation of losses due to evaporation and wind for studied sprinklers in the fixed head sprinkle irrigation systems failed and could not be verified in the city of Sanandaj. The lack of models comprehensive of climate variables, system and hydraulic is reason for their failure for estimation of losses due evaporation and wind for studied zone. Also to evaluate the accuracy of the equations of provided in this study was used NRMSE index. Amount of this index was in the range of 14 to 19 percent for these equations. The accuracy of these models will be assessed good according to the classification of this index.