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A Portable Rainfall Simulator for Plot–Scale Runoff Studies J University of Kentucky UKnowledge Biosystems and Agricultural Engineering Faculty Biosystems and Agricultural Engineering Publications 3-2002 A Portable Rainfall Simulator for Plot–Scale Runoff Studies J. Byron Humphry University of Arkansas Tommy C. Daniel University of Arkansas Dwayne R. Edwards University of Kentucky, [email protected] Andrew N. Sharpley USDA Agricultural Research Service Right click to open a feedback form in a new tab to let us know how this document benefits oy u. Follow this and additional works at: https://uknowledge.uky.edu/bae_facpub Part of the Agriculture Commons, Bioresource and Agricultural Engineering Commons, and the Soil Science Commons Repository Citation Humphry, J. Byron; Daniel, Tommy C.; Edwards, Dwayne R.; and Sharpley, Andrew N., "A Portable Rainfall Simulator for Plot–Scale Runoff tudS ies" (2002). Biosystems and Agricultural Engineering Faculty Publications. 53. https://uknowledge.uky.edu/bae_facpub/53 This Article is brought to you for free and open access by the Biosystems and Agricultural Engineering at UKnowledge. It has been accepted for inclusion in Biosystems and Agricultural Engineering Faculty Publications by an authorized administrator of UKnowledge. For more information, please contact [email protected]. A Portable Rainfall Simulator for Plot–Scale Runoff Studies Notes/Citation Information Published in Applied Engineering in Agriculture, v. 18, issue 2, p. 199-204. © 2002 American Society of Agricultural Engineers The opc yright holder has granted the permission for posting the article here. Digital Object Identifier (DOI) https://doi.org/10.13031/2013.7789 This article is available at UKnowledge: https://uknowledge.uky.edu/bae_facpub/53 A PORTABLE RAINFALL SIMULATOR FOR PLOT–SCALE RUNOFF STUDIES J. B. Humphry, T. C. Daniel, D. R. Edwards, A. N. Sharpley ABSTRACT. Rainfall simulators have a long history of successful use in both laboratory and field investigations. Many plot–scale simulators, however, have been difficult to operate and transport in the field, especially in remote locations where water or electricity is unavailable. This article describes a new rainfall simulator that is relatively easy to operate and transport to and from the field while maintaining critical intensity, distribution, and energy characteristics of natural rainfall. The simulator frame is constructed from lightweight aluminum pipe with a single 50 WSQ nozzle centered at a height of 3 m (9.8 ft). An operating nozzle pressure of 28 kPa (4.1 psi) yields continuous flow at an intensity of 70 mm h–1 (2.8 in. h–1) over a 1.5– Ü 2–m (4.9– Ü 6.6–ft) plot area with a coefficient of uniformity of 93%. Kinetic energy of the rainfall is about 25 J m–2 mm–1 (142.8 ft–lb ft–2 in.–1), approximately 87% of natural rainfall. The simulator can be easily transported by two field personnel and completely assembled or disassembled in approximately 10 min. Water usage is at a minimum as the simulator utilizes only one nozzle. Keywords. Rain simulator, Runoff, Water quality, Erosion. ainfall simulators have been used with much formers such as hanging yarn or tubing tips. Simulators using success throughout the last 75 years to conduct nozzles are generally preferred over drop–former simulators research on infiltration, surface water runoff, and because they have the capability of yielding greater intensi- soil erosion. Meyer (1965) and Young and Burwell ties, are more portable, and can effectively cover larger plot (1972)R pointed out the advantages of using simulated rain as areas. Also, spray–nozzle simulators produce a more ran- opposed to natural rainfall. While natural rainfall is domly distributed rainfall drop pattern compared to drop desirable, as it represents natural conditions at a given place, forming simulators, which tend to produce raindrops of equal data acquisition is very slow and the spatial and temporal size in the same location. distribution of rainfall intensity, duration, and kinetic energy Nozzles used on early rainfall simulators were very simple cannot be controlled (Moore et al., 1983). Rainfall simulators and limited in their applications. Duley and Hays (1932) used have the ability to create controlled and reproducible an ordinary sprinkler can, and Lowdermilk (1930) used two artificial rainfall, which in turn expedites data collection horizontal pipes each fitted with orifices and placed on either (Thomas and Swaify, 1989) and allows comparison of soils side of a plot. Advancements in nozzle design began in 1936 and management variables among locations (Sharpley et al., when the USDA–Soil Conservation Service took interest in 1999). rain simulation for erosion investigation (Mutchler and While rainfall simulators can be very useful tools, there Hermsmeier, 1965). These early nozzles were limited in their are performance limitations (Mech, 1965) due to their ability to simulate the physical characteristics of natural inability to simulate all aspects of natural storms. Limitations rainfall such as kinetic energy and drop–size distribution. in the design tend to be study–specific and usually involve Another major advancement came with the development of plot size, simulated rainfall intensity, and the definitions of the rainulator by Meyer and McCune (1958), which used the terms portable and inexpensive. Several different simula- Veejet 80100 nozzles to produce median drop diameters tors have evolved, differing primarily in method of drop yielding a kinetic energy approximately 80% of natural formation and intensity control (Shelton, 1985). Mutchler rainfall. The rainulator had many desirable characteristics of and Hermsmeier (1965) and Bubenzer (1979) describe natural rainfall not previously found in a single rainfall simulators as being one of two types: 1) simulators that simulator, however, it was complex to operate requiring produce rainfall from nozzles, and 2) simulators using drop much labor and time. Swanson (1965) improved upon Meyer and McCune’s design by developing a simulator that utilized rotating booms that carried continuously spraying Veejet Article was submitted for review in June 2001; approved for 80100 nozzles. The rotating boom simulator was mounted on publication by the Soil & Water Division of ASAE in January 2002. a trailer to help improve mobility, but still required 2 hours The authors are J. Byron Humphry, Graduate Student, Tommy C. for three or four people to disassemble and load the simulator Daniel, Professor, University of Arkansas, Fayetteville, Arkansas; for transport. Using the same nozzle, Foster et al. (1982) Dwayne R. Edwards, ASAE Member Engineer, Professor, University of Kentucky, Lexington, Kentucky; and Andrew N. Sharpley, Soil Scientist, developed a more portable simulator (plot to plot within USDA–ARS, University Park, Pennsylvania. Corresponding author: 30 min) that produced a wide range of intensities up to Tommy C. Daniel, University of Arkansas, PTSC 009, Fayetteville AR 130 mm h–1 (5.1 in. h–1). 72701; phone: 501–575–5720; fax: 501–575–7465; e–mail: tdaniel@ Moore et al. (1983) designed a simulator similar to that uark.edu. described by Foster et al. (1982) using Veejet 80150 nozzles, Applied Engineering in Agriculture Vol. 18(2): 199–204 E 2002 American Society of Agricultural Engineers ISSN 0883–8542 199 achieving a wide range of intensities, acceptable uniformity, USDA–ARS, and USEPA. Currently, there are over 20 scien- and portability. Shelton et al. (1985) improved on the tific collaborators across the United States conducting complex operating mechanisms of the Veejet nozzles by research under the auspices of the Project and rainfall using continuous–application, wide–angle, square–spray simulation techniques serve as the centerpiece for develop- nozzles (Spraying Systems Fulljet 30WSQ and 50WSQ). ing threshold P levels across diverse soil and geographic These investigators were able to utilize continuous–applica- locations, i.e., the relationship between the level of P in the tion without excessive intensities by injecting air into the soil and that contained in the runoff. For the results to be water stream, obtaining acceptable median drop diameters, comparable from a national standpoint, our goal is to have all and finding that drop velocities after 3.0 m (9.8 ft) of fall were investigators use the same simulator and conduct investiga- within 2% of terminal velocities. tions using a common protocol (http://www.soil.ncsu.edu/ Miller (1987) made the simulator described by Shelton sera17). For example, a common rainfall intensity, runoff et al. (1985) more versatile by regulating the water flow sampling, and parameter analysis will be used. Obviously, through the 30WSQ nozzles with the use of a solenoid–oper- new demands and expectations are being focused on the ated valve. Variable intensities were produced by adjusting rainfall simulator. the output of the nozzles using a variable–speed cam–switch Our purpose for designing a new rainfall simulator was to assembly to control the opening and closing of the valves. improve upon the designs of Shelton et al. (1985) and Miller Miller (1987) also found that the kinetic energy distribution (1987) that would allow us to conduct runoff studies in over a 1–m2 (10.8–ft2) plot, produced by the 30WSQ nozzle, remote areas with minimum difficulty and manpower. was within the limits reported for natural rainfall. Miller’s Runoff studies (using rainfall simulators; Edwards et al., simulator sacrificed the continuous flow of Shelton et al. 1992) to relate extractable soil P–to–P
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