Information compiled by Leandro Gonzalez
The Rangeland Hydrology and Erosion Model (RHEM) is a web based tool designed to model and predict runoff and erosion rates on rangelands. This model can also assist in assessing rangeland conservation practice effects. RHEM is a process-based erosion prediction tool specific for rangeland application, based on fundamentals of infiltration, hydrology, plant science, hydraulics and erosion mechanics. It is designed to use data that are routinely collected by rangeland managers and in national monitoring programs such as the Natural Resources Conservation Service (NRCS) National Resource Inventory (NRI). Using RHEM allows land managers to be proactive in preventing accelerated soil loss on rangelands by targeting areas for conservation management that are most vulnerable to soil erosion.
RHEM incorporates the interaction between hydrology and erosion processes, ground cover, plant abundance (canopy cover), and plant growth forms (i.e., sodgrass, bunchgrass, shrubs, and forbs). The flow chart depicted in Figure 1 illustrates the necessary inputs and model execution procedures for the model. Inputs provided by the user include storm characteristics, hillslope shape and slope, dominant plant type, soil cover characteristics (plant canopy, plant base at ground level, rock, litter, cryptogams/microbioitc crusts), and soil texture. Storm characteristics derived from hundreds of long-term climate stations distributed over the western United Sates for various return periods also are available on the web site.
RHEM model simulation inputs and outputs are displayed in tabular and graphical form and multiple runs can be compared to assess how changes in cover characteristics from management practices will influence runoff and sediment (although storm size is the primary determinate of overall erosion and sediment loss).
RHEM allows the user to estimate the vulnerability of a site to soil erosion based on the risk of experiencing a runoff event with a given magnitude (e.g., 10-, 25-, or 50-year return period storm events).
RHEM is currently a single storm runoff and erosion computer model. Parameter estimation equations have been developed based on the measured rangeland erosion plot data for the two primary erodibility and infiltration parameters (Kss and Ke). Parameter estimation for other input parameters, including concentrated flow detachment, are currently under development. The parameter estimation procedures for Kss and Ke are grouped according to dominant plant forms of sod-grass, bunch-grass, and shrubs, with a different set of estimation equations for each grouping. Hence currently, the model may be parameterized and executed for undisturbed rangeland conditions.
• Parameter estimation procedures for the remaining infiltration, runoff, and erosion parameters, which include concentrated flow erodibilities and hydraulic friction factors are underway. Once these procedures are in place, the model will be capable of representing infiltration, runoff, and erosion on both undisturbed and disturbed rangeland hillslopes.
• Procedures will be developed to specifically execute model predictions for NRI data, such that a user may estimate runoff and erosion rates for single storms at NRI sites.
• A risk assessment methodology will be developed that calculates the risk of various sized erosion events occurring at a site of interest in its current or assumed condition.
• The risk assessment methodology using return frequency storm values will be further refined to calculate the risk of various sized erosion events occurring at a site of interest in its current or assumed condition.
Access RHEM Model
RHEM model can be run be following the following link. http://apps.tucson.ars.ag.gov/rhem/register Users need to register to use the tool. The registration is free of cost.
Examples of Rangeland Uses
Nearing et al. 2011. Described the characteristics and advantages of RHEM for rangeland studies. Wei et al. 2008. Described how to use a Dual Monte Carlo approach for a RHEM.
Wei et al. 2007. Utilized a sensitivity analysis method to explore the parameter behavior globally. The method was applied to RHEM using soil responses as a case study.
Rangeland Studies References
Nearing M, Wei H, Stone J, Pierson F, Spaeth K, Weltz M, Flanagan D, and Hernandez M. 2011. A Rangeland Hydrology and Erosion Model. In Transactions of the Asabe. 54 (3): 901-908.
Wei H, Nearing M, Stone J, and Breshears D. 2008. A Dual Monte Carlo approach to estimate uncertainty and its applications to the Rangeland Hydrology and Erosion Model. In Transactions of the Asabe. 51(2): 515-520.
Wei h, Nearing M, and Stone J. 2007. A comprehensive sensitivity analysis framework for model evaluation and improvement using a case study of the Rangeland Hydrology and Erosion Model. In Transactions of the Asabe. 50(3): 945-953
Southwest Watershed Research Center. http://apps.tucson.ars.ag.gov/rhem/links