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The tables provide estimates of the curve number (CN) as a function of hydrologic soil group (HSG), cover type, treatment, hydrologic condition, antecedent runoff condition (ARC), and...
For a more detailed and complete description of land use curve numbers, refer to Chapter Two (2) of the Soil Conservation Service’s Technical Release No. 55 (210-VI-TR-55, Second Ed., June 1986). [1] Composite CNs may be computed for other combinations of open space cover type.
The SCS Runoff Curve Number • The RCN (Runoff Curve Number) method was originally established by the SCS in 1954. • It was originally designed to be an “Inter-Agency” tool for the estimation of runoff. • It was therefore never subjected to peer or journal review by anyone outside the SCS.
HydroCAD ® Stormwater Modeling - Since 1986. What is the Curve Number? Each subcatchment uses a Curve Number (CN) to characterize the runoff properties for a particular soil and ground cover. The CN value is a primary input parameter for the SCS runoff equation, as used by HydroCAD.
The model was developed to provide a consistent basis for estimating the amounts of runoff under varying land use and soil types (Rallison and Miller, 1981). The SCS curve number equation is (SCS, 1972): Qsurf=(Rday−Ia)2(Rday−Ia+S)Q_{surf}=\frac{(R_{day}-I_a)^2}{(R_{day}-I_a+S)}Qsurf =(Rday −Ia +S)(Rday −Ia )2 2:1.1.1.
The Curve Number is a dimensionless parameter indicating the runoff response characteristic of a drainage basin. In the Curve Number Method, the CN is related to land use, land treatment, hydrological condition, hydrological soil group, and antecedent soil moisture condition in the drainage basin. (a) Land Use or Cover.
The runoff curve number was developed from an empirical analysis of runoff from small catchments and hillslope plots monitored by the USDA. It is widely used and is an efficient method for determining the approximate amount of direct runoff from a rainfall event in a particular area.
