The Soil Conservation Service (SCS) curve number (CN) method is one of the most popular methods
for computing the runoff volume from a rainstorm. It is popular because it is simple easy to
understand and apply and stable and accounts for most of the runoff producing watershed
characteristics such as soil type land use hydrologic condition and antecedent moisture
condition. The SCS-CN method was originally developed for its use on small agricultural
watersheds and has since been extended and applied to rural forest and urban watersheds. Since
the inception of the method it has been applied to a wide range of environments. In recent
years the method has received much attention in the hydrologic literature. The SCS-CN method
was first published in 1956 in Section-4 of the National Engineering Handbook of Soil
Conservation Service (now called the Natural Resources Conservation Service) U. S. Department
of Agriculture. The publication has since been revised several times. However the contents of
the methodology have been nonetheless more or less the same. Being an agency methodology the
method has not passed through the process of a peer review and is in general accepted in the
form it exists. Despite several limitations of the method and even questionable credibility at
times it has been in continuous use for the simple reason that it works fairly well at the
field level.
