Question

Why do composite CN’s need to be calculated in hydrology? What purpose do they serve?

Answer 1

The Curve number or simply CN is an empirical parameters used in hydrology for predicting direct runoff or you can say infiltration from rainfall excess.

In general composite CN value generally characterised the runoff properties for a particular soil and ground over. It used as a primary input parameters for run off equation (SCS runoff equation). A high values shows the most of the rainfall to be appears as runoff such as 98 as in the case of pavement. Lower value indicate the increased ability of the soil to retain rainfall and produced less runoff for example 58 value for certain wooded area soil.