Rainfall simulator for laboratory studies

Numerous types of rainfall simulators have been used to stud the fundamenta l behavior of sediment transfer and chemical movement in soil from rainfall . For results of these studies to be representative, it is essential that t he artificial rainfall have characteristics similar to that of natural rain fall. In this study, a number of design modifications were made to a statio nary rainfall device in order to achieve rainfall simulation comparable to natural rainfall. A 1 m x 1 m laboratory-scale rainfall simulator was desig ned and constructed using the positive volume displacement principle to pro vide a precise and broad range of rainfall intensities from 0.025 to 16 cm/ h in increments of 0.025 cm/h. The drop-forming mechanism consisted of a te lescopic arrangement of 21 and 9 gauge stainless steel tubings, producing a mean droplet diameter of 4.5 mm. A drop-size distribution with characteris tics similar to natural rainfall was produced when droplets passed through a suspended drop redistribution screen. When the droplet size spectrum for different height of screen suspension was mapped with the spectrum produced by different intensities of natural rainfall, it was possible to estimate a height of suspension corresponding to a desired application rate with cha racteristics similar to natural rainfall at that given rate. The fully auto mated rainfall simulator was arranged in a closed loop using a feed tank an d automated solenoid valves. The entire rainfall simulation system was inst alled at a height of 14 m to allow droplets up to 4.3 mm diameter to reach 95% of their respective terminal velocities. Flow rate variation among the 216 individual drippers, used in the rainfall simulation design, was less t han 15% of the mean at system application rates less than 1.5 cm/h, and les s than 9% at rates greater than 8 cm/h. Reproducibility of system applicati on rate for a given air inlet tube position was within 1%. The best commerc ial unit available had an advertised +/- 20% variation in system applicatio n rate with only 50% of the range in rate of the unit developed here.