Tripathi, M.P.Sahu, R.K.Mukherjee, A.P.Pandey, V.K.Verma, A.K.Sarkar, Samiran2017-02-132017-02-132003http://krishikosh.egranth.ac.in/handle/1/5810000668Rainfall is the important factor in the process of runoff and soil erosion. Since, its intensity, duration, timing and distribution are beyond our control, the alternative available could be to fabricate a unit of rainfall simulator which can reproduce desirable range of natural rainfall factors. In this study mainly two important criterion has been considered, the mobility and the simulation of erosive rainfall compareable to that of the natural rainfall for the region. A simple rainfall simulator was designed and developed using a commonly avaiable rotary lawn sprinkler. Several hole spacings in the sprinkler arms and reduction in the size of the arms were tested to evaluate the average rainfall intensities and uniformity coefficients. The arrangement of holes and their placement was found considerable for the rainfall having the intensity in the range of 25 to 75 mm/h and the uniformity coefficient was calculated to be 85 per cent and above. Rainfall simulator when operated at 1.25 m height was able to produce acceptable values of average rainfall intensities of 48.5 mm/h and 48.3 mm/h uniformily over the test plot (7.84 m2) at operating pressures of 0.50 kg/cm2 and 0.60 kg/cm2, respectively. Similarly, at 1.5 m height it produces rainfall intensities of 43.1 mm/h and 36.8 mm/h, respectively when operated at pressure haed of 0.60 kg/cm and 0.70 kg/cm , respectively. The cumulative percentage volume of simulated raindrops matched closely with the cumulative percentage volume of natural raindrops. The median drop diameters of simulated rainfall were found to be 2.78 mm, 2.67 mm for 1.25 m height at the pressure heads of 0.50 and 0.60 kg/cm2, respectively whereas for 1.5 m height at 0.60 and 0.70 kg/cm2 pressures median drop diameter was observed to be 2.61 mm and 2.54 mm, respectively. High value of coefficient of determination (0.98) and low value of per cent deviation (9.25 %) revealed that there were a close agreement between median drop diameters of simulated and natural rainfall. The terminal velocity of simulated rain drops were determined and compared with the terminal velocity of natural rain drops. Results reaveled that the terminal velocity produced by simulated rainfall resembles with the natural rainfall for the same fall height and intensities. The designed and developed rainfall simulator was found to be cheaper (Rs.1500.00), portable (15.6 kg), simple in constrcution and easy to operate for simulating the desired range of rainfall characteristics in laboratory condition.enThesis