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.