Measuring and calibrating of rainfall characteristics in tow nozzles rainfall simulator

Small and portable rainfall simulators are essential tools in study of soil erosion and surface hydrology and it provide to repeat natural rainfall characteristics. In addition to the introduction of this device, calibration tests were performed including nozzles discharge evaluation, uniformity test over the plots and raindrop size distribution. The results of nozzles discharge calibration showed that two nozzles discharge at 20, 40, 60 and 80 KPa pressure are similar and there isnt any significant difference between them. To achieve the optimum uniformity of simulated rainfall over the plot uniformity test was performed with changing nozzle distance (50, 60 and 70 cm) and oscillation of nozzles (30, 45 and 60 degrees) at constant operational pressure of 60 KPa. The results showed that the uniformity coefficient at 2m2 plot obtained from 57% to 61% and rainfall intensity changes from 48 to 101 mm/hr. The results of high velocity photography revealed median diameter of raindrop as 2.4 to 2.6 mm.