22-A State-of-the-Art of the SCS-CN Methodology.

Abstract

Any new development of an alternative (or innovation) to extend, generalize, or to improve a methodology requires an understanding of its state-of-the-art. This understanding entails a critical review of historical development,limitations, advantageS, applications, implications, and original intent of the methodology. There exists a significant body of literature published on the Soil Conservation Service-Curve Number (SCS-CN) (presently also known as Natural Resource Conservation Service (NRCS-CN)) model and several recent articles have reviewed the model at length. This paper is an attempt to explore the model further for some of its major discrepancies, such as: (1) implementation of antecedent moisture condition procedure; (2) consideration of 'mean' or 'median' Curve Number (CN) as a representative (quite sensitive) CN for a watershed; (3) initial abstraction (la) and potential maximum retention (S) relationship; (4) use of the potential maximum retention (S) parameter in the model; and (5) effect of storm intensity or duration in runoff estimation. Focusing on these issues, this study finally emphasizes the refinement of the methodology by improving its hydrologic algorithms so that its formulation is more realistic and logical in structure.