Fact Sheet 2009–3085
For more than 50 years, the U.S. Geological Survey (USGS) has been developing regional regression equations that can be used to estimate flood magnitude and frequency at ungaged sites. Flood magnitude relates to the volume of flow that occurs over some period of time and usually is presented in cubic feet per second. Flood frequency relates to the probability of occurrence of a flood; that is, on average, what is the likelihood that a flood with a specified magnitude will occur in any given year (1 percent chance, 10 percent chance, 50 percent chance, and so on). Such flood estimates are needed for the efficient design of bridges, highway embankments, levees, and other structures near streams. In addition, these estimates are needed for the effective planning and management of land and water resources, to protect lives and property in flood-prone areas, and to determine flood-insurance rates.
First posted September 11, 2009
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Feaster, T.D., Gotvald, A.J., and Weaver, J.C., 2009, Methods for estimating magnitude and frequency of floods in rural basins in the Southeastern United States—South Carolina: U.S. Geological Survey Fact Sheet 2009–3085, 2 p.