Determination of Runoff Curve Numbers for the Growing Season Based on the Rainfall–Runoff Relationship from Small Watersheds in the Middle Mountainous Area of Romania

The NRCS-CN (Natural Resources Conservation Service curve number) method, developed by the USDA (U.S. Department of Agriculture) is among most widely used for estimation surface runoff from watersheds. Ever since its introduction in 1950s, although it has been to a great extent engineers and hydrologists, applicability original procedure determine main parameter, number (CN), various regions with diverse environmental conditions, still subject many uncertainties debates. This study presents comparative analysis different methods applied numbers local data four watersheds located central part Romania, within mountain region surrounding Brașov Depression. CN values were not only computed using rainfall–runoff records 1991 2020, but also determined standard NRCS tables documented National Engineering Handbook 630 (NEH-630), comparison purposes. Thus, total 187 five assess accuracy procedures determining values, namely: tabulated (CN selected tables, TAB), asymptotic fitting (AF) both natural ordered data, median (MD), geometric mean (GM) arithmetic (AM) methods. aforementioned was investigated fixed initial abstraction ratio λ = 0.2 adjustment 0.05. Relatively similar results found number-based estimates related field methods, yet slightly better when reduced A high overall performance estimating achieved CN-based exception latter yielding lowest area.