A Runoff and Sediment Routing Model for Open Lot Beef Feeding Facilities

Feedlot runoff is a potential environmental contaminant and requires proper management to minimize impact on water quality. In designing runoff management systems, accurately assessing the amount of runoff that will be generated is of foremost importance. Along with overall quantity of runoff, the temporal pattern, both throughout the year and within an individual storm event, can have important implications for sizing control system components, in determining the performance the control system achieves, and in the overall pollution potential of the feedlot. This review summarizes the hydraulic properties of the feedlot surface, specifically focusing on variables that impact the total volume of effluent generated and the resulting amount of sediment transported. The work cumulates in development of a feedlot runoff routing model, presented as a series of equations that are implemented within the updated Iowa State University-Vegetative Treatment Area model, with a sediment transport/erosion component. Overall, the results indicated that a curve number of 91 was best for estimating runoff volumes, but substantial variation about this value could occur. The calibrated model was able to accurately estimate average total solids concentrations of lots of different size, shape, and surface condition under different hydraulic situations (R2 = 0.92 for calibration and the slope of the measured vs. modeled data was not different than one during model validation). Most calibration and validation feedlots were earthen, had the majority of runoff from rainfall events, had mounds within the pen, and were scraped only once or twice per production cycle; thus model performance may be limited for other situations. The feedlot runoff and sediment routing components were used to assess the impact of various feedlot design characteristics, including feedlot area, aspect ratio, and slope, on solids transport from the feedlot surface. This model can be used to evaluate the risk that feedlot runoff poses to water quality for prioritizing feedlots that are in need of enhanced runoff control systems, and to evaluate the hydraulic and sediment loadings that a runoff control system is required to handle