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information in published or unpublished form is available from other sources. A statistical analysis of these data is the primary basis for the determination of the flow frequency curve for each station. B. Historic Data At many locations, particularly where man has occupied the flood plain for an extended period, there is information about major floods which occurred either before or after the period of systematic data collection. This information can often be used to make estimates of peak discharge. It also often defines an extended period during which the largest floods, either recorded or historic, are known. The USGS includes some historic flood information in its published reports and computer files. Additional information can sometimes be obtained from the files of other agencies or extracted from newspaper files or by intensive inquiry and investigation near the site for which the flood frequency information is needed. Historic flood information should be obtained and documented whenever possible, particularly where the systematic record is relatively short. Use of historic data assures that estimates fit community experi- ence and improves the frequency determinations. C. Comparison With Similar Watersheds Comparisons between computed frequency curves and maximum flood data of the watershed being investigated and those in a hydrologically similar region are useful for identification of unusual events and for testing the reasonableness of flood flow frequency determinations. Studies have been made and published [e.g., (1), (2), (3), (4)]* which permit comparing flood frequency estimates at a site with generalized estimates for a homogeneous region. Comparisons with information at stations in the immediate region should be made, particularly at gaging stations upstream and downstream, to promote regional consistency and help prevent gross errors. *Numbers in parentheses refer to numbered references in Appendix 1. 5