Investigating the application of rainfall simulator for designing micro-catchment systems

Rain simulators are suitable tools for research related to the process of erosion and runoff. However, it is possible to use these simulators on other topics as well. For example, in designing the rainwater catchment systems such as micro-catchments for planting trees on slopes, curve pits in pastures, and determining the size of the water collection pond, knowledge of runoff coefficient and volume of collected water are essential. For this purpose, in a national study, several tons of soil from four selected rainfed lands including Faraghi (Golestan province), Sararoud (Kermanshah province), Kouheen (Qazvin province), and Sarab neniz (Kohgilouyeh and Boyer-Ahmad province) were transferred to the Rainfall Simulation and Erosion Laboratory of the Soil Conservation and Watershed Management Research Institute and after preparation by standard methods, the soils were subjected to a heavy rainfall of 64 mm per hour on three slopes of 6, 12 and 25% for 30 minutes. Such rainfall is unlikely to occur and can be used to design rainwater catchment systems. Outlet flow during the experiment was measured at intervals of 1 to 3 minutes (17 times in total) and the total runoff volume, and then the runoff coefficient and soil infiltration capacity were calculated according to the rainfall volume. In addition, soil infiltration capacity was calculated about 3 to 6 cm per hour. The runoff coefficient of these soils (except Sararoud soil with high infiltration) was calculated between 50 to 90%. According to the characteristics of the soil, soil structure, specific weight, and the amount of organic matter are the factors that determine the infiltration capacity. The volume of runoff (except Sararoud soil) in the most severe events was estimated between 15 to 30 liters per square meter, which is used in the design of the rainwater catchment systems. For soil with high infiltration, it is recommended to compact the soil or use other methods to reduce the infiltration and increase the runoff coefficient.