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A model was developed to predict daily runoff from agricultural watersheds with areas up to 2,590 km². The model is based on the SCS runoff curve number procedure and a soil moisture index. It was designed to have general applicability, computational efficiency, simple inputs, and good prediction accuracy. The model has one parameter, uses a 1-day time interval, and only outputs runoff volume. Inputs are an estimate of the II-condition SCS runoff curve number, measured monthly runoff, daily rainfall, and average monthly lake evaporation. The model is calibrated on a gaged watershed and can be used to extend short periods of record for the calibrated watershed or to predict water yield for nearby ungaged watersheds. In tests with data from 47 watersheds in Texas, the model simulated runoff fairly accurately. Applications include reservoir design, water quality modeling, and flood-control evaluation.
Williams et al. (1976) studied this question.