Abstract
Numerous types of rainfall simulators have been used to study the fundamental behavior of sediment transferand chemical movement in soil from rainfall. For results of these studies to be representative, it is essential that theartificial rainfall have characteristics similar to that of natural rainfall. In this study, a number of design modificationswere made to a stationary rainfall device in order to achieve rainfall simulation comparable to natural rainfall. A 1 m 1 m laboratory-scale rainfall simulator was designed and constructed using the positive volume displacement principle toprovide a precise and broad range of rainfall intensities from 0.025 to 16 cm/h in increments of 0.025 cm/h. The drop-formingmechanism consisted of a telescopic arrangement of 21 and 9 gauge stainless steel tubings, producing a meandroplet diameter of 4.5 mm. A drop-size distribution with characteristics similar to natural rainfall was produced whendroplets passed through a suspended drop redistribution screen. When the droplet size spectrum for different height ofscreen suspension was mapped with the spectrum produced by different intensities of natural rainfall, it was possible toestimate a height of suspension corresponding to a desired application rate with characteristics similar to natural rainfallat that given rate. The fully automated rainfall simulator was arranged in a closed loop using a feed tank and automatedsolenoid valves. The entire rainfall simulation system was installed at a height of 14 m to allow droplets up to 4.3 mmdiameter to reach 95% of their respective terminal velocities. Flow rate variation among the 216 individual drippers,used in the rainfall simulation design, was less than 15% of the mean at system application rates less than 1.5 cm/h, andless than 9% at rates greater than 8 cm/h. Reproducibility of system application rate for a given air inlet tube positionwas within 1%. The best commercial unit available had an advertised 20% variation in system application rate withonly 50% of the range in rate of the unit developed here.
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