EVOLUTION OF METHODS FOR EVALUATING THE OCCURRENCE OF FLOODS by M.A. Benson Prepared by the U.S. Geological Survey Geological Survey Water-Supply Paper 1580-A TABLE OF CONTENTS Abstract Introduction Methods of analyzing flood events     Empirical formulas     Empirical formulas involving frequency     Formulas involving rainfall     Statistical methods Techniques of statistical flood-frequency analysis     Flood-frequency curves         Mathematically fitted curves         Graphical curves     Types of flood data analyzed     Plotting position     Plotting paper Regional flood-frequency analysis     Significance of a single station record     Synthetic 1,000-year flood study     Index-flood method         Base-frequency curves         Mean annual flood         Factors related to mean annual flood         Special treatment for large streams     Multiple-correlation methods     Evaluation of the index-flood method Design frequency relations at gaged sites Predictive value of the flood-frequency relation References ABSTRACT A brief summary is given of the history of methods of expressing flood potentialities, proceeding from simple flood formulas to statistical methods of flood-frequency analysis on a regional basis. Current techniques are described and evaluated. Long-term flood records in the United States show no jusitification for the adoption of a single type of theoretical distribution of floods. The significance and predictive value of flood-frequency relations are considered. Because of the length of flood records available and the interdepdendence of flood events within a region, the probable long-term average magnitudes of floods of a given recurrence interval are uncertain. However, if the magnitudes defined by the records available are accepted, the relative effects of drainage-basin characteristics and climatic variables can be determined with a reasonable degree of assurance. LizardTech's Djvu plug-in is needed to view these reports. CLICK HERE TO VIEW THE ENTIRE REPORT For questions or comments, contact K. Van Wilson.