Water-Resources Investigations Report 02-4168
Compiled by K.G. Ries III and M.Y. Crouse
This report is available as a pdf.
For many years, the U.S. Geological Survey (USGS) has been developing regional regression equations for estimating flood magnitude and frequency at ungaged sites. These regression equations are used to transfer flood characteristics from gaged to ungaged sites through the use of watershed and climatic characteristics as explanatory or predictor variables. Generally, these equations have been developed on a Statewide or metropolitan-area basis as part of cooperative study programs with specific State Departments of Transportation.
In 1994, the USGS released a computer program titled the National Flood Frequency Program (NFF), which compiled all the USGS available regression equations for estimating the magnitude and frequency of floods in the United States and Puerto Rico. NFF was developed in cooperation with the Federal Highway Administration and the Federal Emergency Management Agency. Since the initial release of NFF, the USGS has produced new equations for many areas of the Nation. A new version of NFF has been developed that incorporates these new equations and provides additional functionality and ease of use.
NFF version 3 provides regression-equation estimates of flood-peak discharges for unregulated rural and urban watersheds, flood-frequency plots, and plots of typical flood hydrographs for selected recurrence intervals. The Program also provides weighting techniques to improve estimates of flood-peak discharges for gaging stations and ungaged sites. The information provided by NFF should be useful to engineers and hydrologists for planning and design applications.
This report describes the flood-regionalization techniques used in NFF and provides guidance on the applicability and limitations of the techniques. The NFF software and the documentation for the regression equations included in NFF are available at http://water.usgs.gov/software/nff.html.
Abstract
Purpose
Report Format
How to Obtain the NFF Software and Documentation
Acknowledgments
INTRODUCTION
INDEX-FLOOD PROCEDURES
ORDINARY-LEAST-SQUARES REGRESSION
WEIGHTED- AND GENERALIZED-LEAST-SQUARES REGRESSION
REGION-OF-INFLUENCE REGRESSION
INTRODUCTION
WATERSHED AND CLIMATIC CHARACTERISTICS
HYDROLOGIC FLOOD REGIONS
MEASURES OF ACCURACY
TECHNIQUES FOR WATERSHEDS THAT SPAN REGIONAL/STATE BOUNDARIES
WEIGHTING OF INDEPENDENT ESTIMATES OF RURAL FLOOD FREQUENCY
Weighting for Streamgaging Stations
Weighting for Ungaged Sites
INTRODUCTION
NATIONWIDE URBAN EQUATIONS
LOCAL URBAN EQUATIONS
MEASURES OF EXTREME FLOODS
EXTRAPOLATION FOR THE 500-YEAR FLOOD
REFERENCES
APPENDIX A—
DOWNLOADING AND INSTALLING THE PROGRAM
STARTING THE PROGRAM
MAIN WINDOW
Menu Items
File menu
Graph menu
Help menu
Manual
Web site
About
EDIT SCENARIO WINDOW
FREQUENCY WINDOW
HYDROGRAPH WINDOW
WEIGHT WINDOW
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