بررسی دقت برخی از مدل‌های برآورد تلفات ناشی از تبخیر و باد در سیستم‌ آبیاری بارانی کلاسیک ثابت

Due to widely used sprinkle irrigation systems, it is necessary to develop a model for estimating evaporation and wind drift losses. Many factors are effective on 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 and the system parameters. 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) for estimating the 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 types of 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 a dry horizontal electro pump was used. The main pipe was of polyethylene with an outside diameter of 160 mm. The butterfly valve in the bypass pipe was used to adjust the pressure of the model. A sub main polyethylene pipe was used with a diameter of 50 mm and a length of approximately 120 m to convey water to the sprinkler. In this study a riser with 165 cm height was considered. 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 greater than the diameter of the riser. The discharge of sprinklers were measured by volumetric method. The studied zone was a gridded region with an area of 60 × 60 square meters. The studied zone was gridded by using plastic meter and wooden sticks (3m×3m), and water collecting buckets (with a height of 90 mm and internal diameter of 80 mm) were installed. The minimum test time was 1 hour. This investigation is performed to assess effect of different intensities of wind and pressure amount at 4 different system pressure (3, 3.5, 4 and 4.5 bar), at 2 types of wind speed (0-1.8 calm wind, 1.8-4.4 average wind) on water losses. On-site testing wind speed with a handheld anemometer at a height of about 2 meters were measured and temperature and relative humidity were measured 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) for 3 sprinklers ZM22, AMBO and ZK30 had significantly different from the measured losses due to evaporation and wind. Also, computational results of Frost and Schwalon were significantly different in both sprinklers of Ambo and ZK30 at 5 and 1% significant level, respectively and were not significantly different in ZM 22. In both ZM22 and ZK30 sprinklers, computed results by Trimmer (1990) method were not significantly different with measured losses due evaporation and wind, but in Ambo sprinkler was significantly different at 1% significance level. For all of three studied sprinkler, the Montero et al. (2000) equation overestimated the water losses due to evaporation and wind, but Keller and Bliesner (1990) method underestimated the losses. Also the results of Frost and Schwalon (1955) in both of Ambo and ZK30 sprinkler and Trimmer method in the Ambo sprinkler have underestimated the losses. Also, based on NRMSE, the accuracy of all models were weak to estimate losses due to evaporation and wind in all three studied sprinklers. Accuracy of the trimmer (1987) equation was at the border of moderate to weak for ZK30 sprinkler.
The results of evaluating the models’ accuracy have shown that the used models are not suitable for estimating the losses due to evaporation and wind for studying sprinklers in the fixed head sprinkle irrigation systems in the city of Sanandaj. The failure of studying models was because of lack of consideration of all effective climatic variables, system and hydraulic in estimating the losses due to evaporation and wind. Also an equation was proposed in this study for in estimating the losses due to evaporation and wind in Sanandaj city. The accuracy of the proposed equation was evaluated by NRMSE criterion. The NRMSE values for the proposed equation were in the range of 14 to 19 percent. Therefore, the accuracy of the proposed equation is good according to the classification of this index and it can be used for estimating the losses due to evaporation and wind in Sanandaj city.