Synthesized flood frequency for small urban streams in Tennessee

Bridge, culvert, and highway design often require knowledge of the magnitude and frequency of flood discharge from small streams where the drainage basin is urbanized. The results of a 6-year study by the U.S. Geological Survey provide methods for estimating flood magnitudes for selected frequencies on small streams draining urban areas in Tennessee. A total of 22 rainfall-runoff sites located in basins with drainage areas of 0.21 to 24.3 square miles in size and in municipalities with populations between 5,000 and 100,000 were used to derive regionalized flood-frequency equations. Impervious area, measured from recent aerial photographs, ranged between 4.7 percent and 74.0 percent of the basin. The equations were derived by multiple regression analyses of snythetic flood-frequency estimates, derived from a rainfall-runoff modeling procedure, versus physical basin characteristics and a precipitation factor. These equations can be used to estimate the magnitude of future floods with recurrence intervals of 2 to 100 years on ungaged urbanized streams in Tennessee. One equation for each recurrence interval applies statewide. Flood-frequency estimates for stations used in the analyses and example computations demonstrating applications of the regression equations to urban streams in Tennessee are given in the report. (USGS)