Magnitude and frequency of flood volumes for urban watersheds in Leon County, Florida

Techniques are provided for estimating runoff magnitudes for urban-flow streams in Leon County, Florida, for recurrence intervals of 2, 5, 10, 25, 50, 100, and 500 years. Synthetic runoff volumes were generated by using a calibrated lumped-parameter rainfall-runoff model, pan evaporation data from Milton, Florida, and long-term unit rainfall records from Thomasville-Coolidge, Georgia, and Pensacola, Florida. The synthetic runoff volumes were used to develop station runoff-frequency relations which were used in multiple linear regression analyses to derive regional equations relating runoff to basin characteristics. The significant basin characteristic was impervious area. The average standard error of regression was + or - 16 percent for all recurrence intervals except the 2-year, + or - 18 percent and the 500-year + or - 17 percent. (USGS)