RUNOFF, EROSION, AND SIZE DISTRIBUTION OF SEDIMENT FROM BEEF CATTLE FEEDLOTS

The size distribution of sediment in runoff from feedlot surfaces influences erosion rates and settling velocity. The objectives of this study were to: (1) measure runoff erosion, and size distribution of sediment in runoff from feedlot surfaces containing varying amounts of unconsolidated surface material (USM), and (2) determine the effects of varying runoff rate on erosion and sediment size distribution. Simulated rainfall was applied to 0.75 m wide by 2 m long plots located within feedlot pens. Sieve and pipette analyses were used to measure the diameters of the eroded materials. No significant differences in runoff and erosion were found among the treatments with varying amounts of USM. Values for D-50, the size for which 50% of the sediment is smaller, were 36 mu m or less for each of the treatments containing varying amounts of USM. The surfaces containing 0 or 6.7 kg m(-2) of USM had D-50 values that were significantly greater than those with 13.5 or 26.9 kg m(-2) of USM. An increase in runoff rate resulted in significantly greater erosion. The proportion of sediment fractions 31 mu m and larger consistently increased as runoff rate became greater. No significant differences in D-50 values were found for runoff rates varying from 0.5 to 9.7 kg min(-1). The D-50 value of 310 mu m obtained at a flow rate of 15.3 kg min(-1) was significantly greater than measurements determined at the other runoff rates. Both erosion and size distribution of sediment in runoff from feedlot surfaces are significantly influenced by runoff rate.