A Hand-Portable Single Nozzle Rainfall Simulator Designed for Use on Steep Slopes

Abstract

The objective of this study was to develop a smaii plot (1 m*) rainfall simulator operational on steep terrain in the Guadalupe Mountains of New Mexico. The simuiator developed is bandportable and consists of a spray head assembly mounted on 3 adjustable legs. A 946-liter tank equipped with a gasoline powered pump was connected to the spray head assembly via rubber garden hoses. On steep slopes gravity provided sufficient pressure to operate the simulator. Site selection was limited to areas where the water tank could be located in a suitable upsiope position. The simuiator has been used for 2 years on 170 plots and has proved durable. Advantages of this device are the low cost of construction and operation, and the flexibility in plot-site selection it provides. The principal disadvantages are associated with the single stationary nozzle, such as uneven application of water at small drop sizes and low kinetic energies. An ideal rainfall simulator has yet to be developed. Those that most closely reproduce rainfall patterns and intensity are expensive and require large expenditures of manpower for setup and operation (Foster et al. 1979). However, rainfall simulators, even though imperfect, are essential tools for investigating hydrologic processes on arid and semiarid rangeland where rainfall events are sporadic. Simulator experiments can be used to estimate infiltration, interrili erosion runoff rates, and chemical water quality for given storm events. Impacts of range management practices (grazing strategy, brush control, reseeding) on the watershed can also be evaluated using rainfall simulators. Rainfall simulators can be used to collect data in a relatively short period, rather than the 10 to 20 years needed to collect sufficient information from natural rainfall events. Rainfall simulators also provide maximum control over plot conditions and rainfall characteristics. Rainfall simulators in common use by range watershed scientists are the mobile drop-forming (Blackburn et al. 1974), Rocky Mountain infiltrometer (Dortignac 1951) and versions of the Purdue type (Bertrand and Parr 1961). Ail the above provide mobility, but use of each is restricted to relatively flat terrain. Hand-portable infiltrometers have been developed (Adams et al. 1957, McQueen 1963, Seiby 1970, Munn and Huntington 1976, Malekuti and Gifford 1978) and are more suitable for rugged terrain. Munn and Huntington (1976) report the Tahoe Basin infiltrometer to be functional on slopes to 60%. Hand-portable infiltrometers, however, have not been widely used, perhaps because many are bulky, heavy, require pumps or motors, or have a limited water supply. This paper presents the construction, operation, rainfall characteristics, and limitations of a hand-portable small rainfall simulator developed for use on steep slopes in the Guadalupe Mountains of New Mexico.