Development of an Evaporative-Runoff Model for Cattle Feedlot Pens

Abstract

Proper feedlot planning entails design of adequate runoff storage for rainfall and snowmelt events. The general standard for this as been use of the SCS curve number (CN) of 90 for a one in 25 year-24 hr event (U.S.) Towards improvement of processes controlling feedlot runoff and design standards we have developed a daily runoff model that will predict the occurrence and amount of runoff from cattle earthen floor feedlots. Key components necessary for the model to properly represent cattle feedlots are: manure pack thickness, cattle stocking rate (rate of water and solid excretion), manure pack physical properties (e.g., water retention, drying rate, hydraulic conductivity), change in manure pack properties with moisture, and surface detention. Daily potential evaporation and precipitation are used with a soil-water drying function and the SCS runoff model. The model was developed with measured runoff data from one study and evaluated against a second study. The model was then run with 62 years of climate data to identify the likelihood of a storage pond in a sub humid climate or a semi arid climate being overfilled. Results from the model were compared against the standard using a CN of 90 and a variable CN using an antecedent precipitation index. The model adequately predicts the occurrence and amount of runoff from rain events, but further understanding of manure pack retention properties are needed.