Magnitude and frequency of floods from urban streams in Leon County, Florida

Techniques are provided for estimating flood magnitudes for urban-flow streams in Leon County, Florida, for recurrence intervals of 2, 5, 10, 25, 50, 100, and 500 years. Synthetic flood peaks 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-Collidge, Georgia, and Pensacola, Florida. The flood peaks were used in multiple linear regression analyses to derive regional equations relating flood magnitude to basin characteristics. Significant basin characteristics were drainage area and impervious area. The average standard error of prediction ranged from + or - 32 percent for the 5-year recurrence interval to + or - 47 percent for the 500-year recurrence interval flood. (USGS)