EVALUATING SAMPLING STRATEGIES FOR RAINFALL SIMULATION STUDIES

Abstract

Rainfall simulation experiments were carried out on an outdoor experimental plot in the Department of Hydrology at IIT Roorkee, India using a rainfall simulator fabricated with four fixed stand pipes on which a header with 11 nozzles attached to it. The height of the header of the rain simulator can be adjusted up to 3.35m. Six types of full cone nozzle with different orifice diameter were used. Studies were carried out on 3m x 1.5m plot for different pressure and different heights. In order to determine the rainfall intensity and uniformity coefficient, several tests were carried using six sets of nozzles (B1/8GG-SS4.3W, B1/4GG-SS10W, B1/4GG-SS14W, B3/8GG-SS17W, B1/2G-SS30W and B1/2GG-SS40W) with four different header heights (2m, 2.5m, 3m & 3.35m) and three different operating pressure heads (0.4kg/cm2, 0.8kg/cm2 and 1.6kg/cm2). Three replications of same nozzle at same height and same pressure head were carried out. Taguchi method was used with objective to identify the key factor that contributed most to the rainfall intensity. It was found that percentage contribution of key factor nozzle size was 62.41% which means nozzle size is a sensitive key factor that influence more on the rainfall intensity optimum condition is observed at pressure of 1.6 kg/cm 2, a height of 2m and nozzle orifice dia. of 3.6 mm. A multiple linear equation (R2 = 0.941) was developed to calculate rainfall intensity as a function of operating pressure head, height of nozzle header and orifice diameter of nozzle. Developed equation can be used to know rainfall intensity based on operating parameters of the rainfall simulator. The measured rainfall intensity ranged from 55mm/hr to 780mm/hr and uniformity coefficient ranged from 84.49% to 92%.