Flood-frequency analysis for small natural streams in Georgia

Abstract

Flood information from 104 project basins (0.1 to 20 square miles) and data available from 170 larger basins (20 to 1,500 square miles) are analyzed to provide planners and designers with relations for estimating the magnitude and frequency of flood-peak discharges on small natural streams in Georgia. In 1963 the U.S. Geological Survey, in cooperation with the Georgia Department of Transportation and the Federal Highway Administration,U.S. Department of Transportation, began this program to collect and analyze flood-peak data from small drainage basins. More than 90 percent of the project activity was directed toward the acquisition and processing of data for more than two thousand rainfall-runoff periods occurring during 1964-74 at the 104 project stations. Storm rainfall data were computed at 5-minute intervals from records of six long-term (about 75 years) National Weather Service stations. The U.S. Geological Survey mathematical rainfall-runoff model is used to synthesize long-term flood records for about 80 percent of the project stations. Station flood-frequency data are developed, using the log-Pearson Type III distribution with regionalized skew coefficients. Multiple regression analysis is used to define relations between flood-frequency station data for small and large streams and 10 physical and climatological basin characteristics. The analysis indicates the drainage-basin size is the most significant variable. Five regions having distinct flood-peak characteristics are delineated. One of these regions, known as the Sand Hills, has not been delineated previously as an area of "low" flood runoff. The developed relations, expressed as equations and nomographs, are considered usable for virtually any site in Georgia where ne drainage area is between 0.1 and 20 square miles, and the flow is natural.