Prediction of Flood Volume from Small Humid Region Watersheds

The Soil Conservation Service approach of soil-cover complex concept was modified and refined for predicting runoff volumes from individual storms. Two definitions of runoff volume were examined. For each definition two approaches were investigated: (1)Predicting runoff volume with soil-cover information and the SCS rainfall-runoff model; and (2) correlating runoff volumes with climatic and watershed parameters. The first approach requires calibration of watershed wetness while the second use a direct correlation. Prediction equations were developed with 210 events from 15 Pennsylvania and Ohio watersheds less than 20 sq miles. Both approaches were tested on the five reserved watersheds with satisfactory results. The first approach was found superior to the second. The frequency distribution of watershed wetness associated with flood events is also presented.