Abstract— Comparison of CN estimation approaches. The Curve Number (CN) method used for estimating direct runoff depths from rainstorms (developed by NRCS in 1954) is based on a CN parameter (representing the hydrological properties of a catchment) and a λ parameter (representing the initial abstraction ratio Ia/S). In this paper, the CN parameter is determined for 10 small Slovak basins using the original SCS-CN method (CNtabulated) and empirically from rainfall-runoff events for a 13-year period using four different approaches (asymptotic fitting, arithmetic, median, and a method used by Hawkins et al. ) for both natural and ordered P-Q pairs (CNempirical). The CNempirical numbers were evaluated and consequently used to determine the direct runoff for both λ equal to 0.2 and 0.05. The results show differences among the selected approaches that indicate variances in the direct runoff computed. The large range of the empirical CN numbers indicates uncertainty. However, the NRCS does not define the uncertainty of the tabulated curve numbers either, and the original data is not available. As a result, this paper will highlight the uncertainty of tabulated CN numbers.
Keywords— Curve Number method, Rainfall-runoff events, Asymptotic fitting.
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