Project Overview

Full Title
Flood Frequency

Location
 Statewide

Cooperating Agencies
North Carolina Department of Transportation

Project Chief
D. G. Smith
dgsmith@usgs.gov

Period of Project
Ongoing

USGS IN YOUR STATE

USGS Water Science Centers are located in each state.

Flood Frequency

Project Summary

Contentnea Creek at Hookerton during extreme flooding caused by Hurricane Floyd in 1999.

Background

Reliable estimates of the magnitude and frequency of floods are needed for numerous design and management functions throughout North Carolina. For U.S. Geological Survey (USGS) streamgage sites, where 10 or more years of annual peak-flow data have been recorded, estimates of flood frequency can be computed using statistical analysis. Flood-frequency estimates at gaged sites can be regionalized, or extended in space, to develop estimates of flood-frequency at ungaged sites.

Objectives

The flood-frequency project was developed in cooperation with the North Carolina Department of Transportation (NCDOT) to provide information about location, basin boundaries, attributes, and flood frequency for specific stream sites using a map-based interface. Using peak-flow data compiled through 1996, computed flood-frequency estimates are presented on the Web page North Carolina Flood-Frequency Statistics for gaged sites with 10 or more years of annual peak-flow record. For ungaged sites, the site information and predictive equations that can be used to calculate flood-frequency estimates also will be presented.

Approach

Flood-frequency estimates for gaged stream sites with more than 10 years of annual peak-flow record are presented through a series of interactive maps on the USGS North Carolina Web page. The USGS has compiled information that can be used to calculate flood-frequency estimates for approximately 15,000 ungaged stream sites in North Carolina. Information for these ungaged sites will be added systematically to the USGS Web page with the appropriate predictive equations. Site information and predictive equations will be presented together for each individual stream site in order to provide the user with a convenient means of calculating flood-frequency estimates. It is anticipated that information for ungaged sites will be added to the Web page periodically and completed by September 30, 2005. Further details and computational methods can be found in Bulletin 17B (Hydrology Subcommittee on the Interagency Advisory Committee on Water Data, 1981), Robbins and Pope (1996), and Pope and others (2001).

References

• Hydrology Subcommittee of the Interagency Advisory Committee on Water Data, 1981, Guidelines for determining flood frequency: Reston, VA., U.S. Geological Survey Bulletin 17B, Office of Water Data Collection, 183 p. (corrected editorially in March 1982).
   
• Pope, B.F., Tasker, G.D., and Robbins, J.C., 2001, Estimating the magnitude and frequency of floods in rural basins of North Carolina - Revised: U.S. Geological Survey Water-Resources Investigations Report 01-4207, 42 p. + app.
  Abstract · Full Text
• Robbins, J.C., and Pope, B.F., 1996, Estimation of flood-frequency characteristics of small urban streams in North Carolina: U.S. Geological Survey Water-Resources Investigations Report 96-4084, 19 p. + app.
  Abstract