Curve Number Approach for Estimating Runoff from Turf

The curve number equation is one of the simplest and most commonly used models for estimating surface runoff. However, its applicability to turfgrasses has not been previously demonstrated. This study evaluated the approach by comparing model estimates with measured runoff data from turf field plots in six different states, including three different soil hydrologic groups, four turfgrasses, and a range of antecedent moisture and turf conditions. A set of curve numbers were developed for short and long grasses with and without thatch, and curve number selection was based on linear functions of 5‐d antecedent precipitation. With the standard growing season antecedent moisture limits of 36 mm and 53 nun, the curve number model explained 78% of the observed variation in runoff and underpredicted the mean event runoff by 15%. With a downward adjustment of these limits to 22 nun and 53 mm in split‐sample calibration, the underprediction of means was reduced to less than 3%. More significantly, the model mean for the largest observed events was within 6% of the observed mean. Provided model results are interpreted in a statistical sense rather than as individual events, the curve number model, as modified in this study, is a relatively accurate means of estimating turf runoff.