Magnitude and frequency of floods

Abstract

Estimation of the 100-year flood at hundreds of thousands of sites will be required for implementation of the Federal Flood Insurance Act. Other aspects of planning and drainage design require innumerable calculations of floods and their frequency. Modern advances in statistical theory have recently been applied to various aspects of these problems. This review summarizes the major works that have contributed to the state of the art. The discussion is presented in a pragmatic form ratner than in historical sequence. Text is aimed at engineers and planners who have not had the benefit of time to study the parlance of mathematical probability. Sufficient statistical theory is explained to give an appreciation of its limitations. Thus, the output from computer programs, which are disseminated so readily by big brother and other experts, can be viewed in better perspective by the user. The latest status of the log-Pearson Type III distribution, recomended by the Water Resources Council, is presented. Vital importance of graphical examination of data is stressed. Mathematical analysis to supplement this is explained, and examples show how the five most useful probability distributions can be fitted by a hand calculator. /Author/