Overview

Methods for estimating the magnitude of floods for selected percent chance exceedance probabilities are presented for ungaged streams in Florida that are not sub stantially affected by regulation, channelization, or urban development. Flood-frequency flows also are presented for 275 Florida streamgages used in the regional regression analy-sis. Regression relations used generalized least-squares regres-sion techniques to estimate flood magnitude and frequency on ungaged streams as a function of basin drainage area and a storage factor. These regression equations were developed for four different hydrologic regions in Florida. The flood regions were delineated based on plotted residuals, previous flood-frequency studies, and geologic, physiographic, and drainage-area maps. The methods used in this report are based on flood-frequency characteristics for 305 streamgages including 275 in Florida and 30 in the adjacent states of Georgia and Alabama, all having at least 10 years of record through September 2006. For the larger streams outside the limits of the regression equations-the Apalachicola River and Suwannee River at Ellaville and below-the report includes graphical relations of peak flow to drainage area.