Hydraulic Characteristics of Unconsolidated Surface Materials Located Within Feedlots

Abstract

Beef cattle feedlots contain unconsolidated surface material that accumulates within feedlot pens during a feeding cycle. Runoff from feedlot surfaces is diverted into settling basins. The storage capacity of settling basins will be substantially reduced if large quantities of solid material are transported in runoff from feedlot surfaces. The objective of this study was to identify the hydraulic conditions that will not move unconsolidated surface materials located within feedlots in order to minimize sediment transport. Selected sizes and a composite sample of unconsolidated surface material were placed within 0.75 m wide by 4.0 m long metal frames and flow was then introduced at the top of the frames in successive increments. The discharge rate and flow velocity necessary to cause movement of unconsolidated surface material was measured. Hydraulic measurements were used to calculate the ratio of critical flow depth to particle diameter, critical shear velocity, critical Reynolds number, critical shear stress, critical dimensionless shear stress, and critical boundary Reynolds number which for the composite material were 0.667, 0.0737 m s-1, 678, 3.77 Pacal, 0.0504 and 553, respectively. Regression equations were derived which related selected hydraulic parameters to particle diameter. Roughness coefficients are used to calculate time of concentration, determine flow velocity, and simulate runoff hydrographs. Darcy-Weisbach roughness coefficients were calculated for each particle size class and the composite sample at varying flow rates. The information presented in this study can be used to identify the hydraulic conditions required to move unconsolidated surface material located within feedlots.