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<br />I. Introduction <br /> <br />In December 1967, Bulletin No. 15, "A Uniform Technique for Determining <br />Flood Flow Frequencies," was issued by the Hydrology Committee of the <br />Water Resources Council. The report recommended use of the Pearson Type <br />III distribution with log transformation of the data (log-Pearson Type <br />III distribution) as a base method for flood flow frequency studies. As <br />pointed out in that report, further studies were needed covering various <br />aspects of flow. frequency determinations. <br />This guide is an extension and update of Bulletin No. 15. It <br />provides a more complete guide for flood flow frequency analysis incorpo- <br />rating currently accepted technical methods with sufficient detail to <br />promote uniform application. This guide is limited to defining flood <br />potentials in terms of peak discharge and exceedance probability at <br />locations where a systematic record of peak flood flows is available. <br />The recommended set of procedures was selected from those currently <br />used or described in the literature. Selection was based on studies <br />conducted for this purpose at the Center for Research in Water Resources <br />of the University of Texas at Austin (summarized in Appendix 14) and on <br />studies by the Work Group on Flood Flow Frequency. <br />Major problems are encountered when developing guides for flood <br />flow frequency determinations. There is no procedure or set of procedures <br />that can be adopted which, when rigidly applied to the available data, <br />will accurately define the flood potential of any given watershed. <br />Statistical analysis alone will not resolve all flood frequency problems. <br />As discussed in subsequent sections of this guide, elements of risk and <br />uncertainty are inherent in any flood frequency analysis. User decisions <br />must be based on properly applied procedures and proper interpretation <br />of results considering risk and uncertainty. Therefore, the judgement <br />of a professional experienced in hydrologic analysis will enhance the <br />usefulness of a flood frequency analysis and promote appropriate applica- <br />tion. <br /> <br />1 <br />