Quantifying Excess Stormwater Using SCS-CN-Based Rainfall Runoff Models and Different Curve Number Determination Methods

Estimation of excess storm water is among the most basic hydrological challenges for hydrologists and engineers. The initial abstraction ratio lambda (= 0.2) assumed in the original U.S. Soil Conservation Service curve number (SCS-CN) is ambiguous and must be calibrated from rainfall-runoff measurements for better runoff estimation. Eight different models including the original SCS-CN model, modified models in spired by it, and three newly proposed models were investigated to assess the accuracy of runoff estimation using rainfall-runoff measurements from 15 watersheds in South Korea. Different methods for CN determination were evaluated to see the effect of CN and lambda on runoff estimation. The optimized lambda and CN exhibited better results than fixed values as in the original SCS-CN model. Using three different goodness-of-fit statistics to assess the accuracy of the estimates, our proposed models outperformed in all watersheds in the study area when compared with the original SCS-CN model and some of its modified models. (C) 2014 American Society of Civil Engineers.