Technique for estimating the magnitude and frequency of floods in St. Louis County, Missouri

Equations and nomographs in.this report can be used to estimate peak flood-discharges having recurrence intervals up to 100 years in rural and urban areas of St. Louis County, Mo. The basin characteristics significant at the 5-percent probability level were drainage area and percentage imperviousness. Drainage area can be measured from maps, while percentage of imperviousness can either be measured from aerial photographs or estimated from land-use projections. These equations are based upon the analysis of hydrologic data collected at 30 continuous-recording gaging stations with drainage areas ranging from 0.8 to 39.0 square miles, and with impervious areas ranging from 1 to 32 percent.