Investigation of Curve Number Procedure

The curve number procedure of the Soil Conservation Service is investigated to establish a logically consistent, experimentally verifiable system. Several traditional aspects of the system are explored. These include conflicting definitions of the AMC‐II condition, physical significance of the maximum potential retention, and the use of the runoff equation to estimate infiltration rate. To develop a consistent system, the runoff equation is taken to be a transform between a rainfall frequency distribution and a runoff frequency distribution. The curve numbers are treated as random variables with the curve numbers associated with antecedent moisture condition II (AMC‐II) representing the central tendency. Those associated with AMC‐I and AMC‐III are shown to be representative of extremes of the distribution.