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<br />The USGS has traditionally been involved in the <br />development of statistical methods for estimating the <br />magnitude and frequency of floods at ungaged sites; <br />specifically, methods that relate flood characteristics at <br />gaging stations to watershed and climatic characteris- <br />tics through the use of regression analysis. These meth- <br />ods enable the transfer of flood characteristics from <br />gaging stations to ungaged sites simply by determining <br />the needed watershed and climatic characteristics for <br />the ungaged site. Since 1973, regression equations for <br />estimating flood-peak dischaIges for rural, unregulated <br />watersheds have been published, at least once, for <br />every State and the Commonwealth of Puerto Rico. For <br />some areas ofthe Nation, however, data are still inade- <br />quate to define flood-frequency characteristics. Regres- <br />sion equations for estimating urban flood-peak <br />discharges for several metropolitan areas in at least 13 <br />States are also available. Typical flood hydro graphs <br />corresponding to a gi ven rural and ( or) urban peak dis- <br />charge can also be estimated by procedures described <br />in this report. The statewide flood-frequency reports <br />were prepared by the USGS, generally in cooperation <br />with a given State Department of Transportation, and <br />were published either by the USGS or the State Depart- <br />ment of Transportation. The USGS, in cooperation <br />with the Federal Highway Administration and the Fed- <br />eral Management Emergency Agency, has compiled all <br />the current (September 1993) statewide or metropolitan <br />area regression equations in the NFF Program. <br /> <br />Purpose <br /> <br />The purpose of this report is to document and <br />describe the f1ood.frequency regression equations and <br />procedures in the NFF computer program, a program <br />that provides engineers and hydrologists easy-to-use <br />methods for estimating flood-peak dischaIges and flood <br />hydrographs for planning and design applications. This <br />report summarizes the current statewide regression <br />equations that have been approved for publication as of <br />September 30, 1993. The compilation of all USGS- <br />developed regression equations into a single report and <br />computer program, and the compilation of figures and <br />other needed input allows the analyst to quickly and <br />easily estimate flood-frequency characteristics for <br />ungaged stream sites throughout the United States. It is <br />anticipated that this report and the NFF program will be <br />updated every couple of years as new statewide regres- <br />sion equations become available. <br /> <br />Report Format <br /> <br />This report is divided into two major parts. The <br />front sections give an overview of flood regionalization <br />methods, summarize the characteristics of the estimat- <br />ing techniques, and describe their applicability and lim- <br />itations. The latter sections summarize flood- <br />estimation methods in each State and provide refer- <br />ences to the applicable statewide or metropolitan area <br />flood-frequency reports, Many persons contributed to <br />the development of the computer program and this <br />associated documentation. Persons responsible for pre- <br />paring each section of this report are so noted. <br /> <br />Most maps or figures needed to make flood esti- <br />mates, such as maps delineating flood regions or maps <br />of climatic variables characteristics, are reproduced in <br />this report. However, the user will occasionally be <br />required to refer to the appropriate State reports to <br />obtain the input needed for the application of the <br />regression equations. Watershed characteristics needed <br />in application of the regression equations must be mea- <br />sured from the best-available topographic maps <br />obtained by the user. <br /> <br />Information on computer specifications and the <br />computer program are given in appendixes. Instruc- <br />tions for installing NFF on your own personal com- <br />puter are given in Appendix A. A description of the <br />NFF program and the associated data base of regres- <br />sion statistics is given in Appendix B. <br /> <br />ACKNOWLEDGMENTS <br /> <br />The authors would like to acknowledge the con. <br />tributions of Eugene Cookmeyer, a former employee of <br />the USGS, who wrote the original version of the NFF <br />program and compiled the initial state-by-state data <br />base of regression coefficients. We also wish to <br />acknowledge the contributions of Dr. William Rogers, <br />Assistant Professor, Department of Electrical and <br />Computer Engineering, University of Texas, Austin, <br />Texas, for making revisions and improvements in the <br />original program and for revising the state-by-state <br />data base of regression coefficients. Dr. Rogers also <br />revised the program so that it would run on a greater <br />variety of personal computers. <br /> <br />2 <br /> <br />Nationwide Summary 01 U.S. Geological Survey Reglona' Regression Equstionslor Estimating Magnltucle end Frequency 01 <br />Flood. for Ungased Site.. 1993 <br />