Laserfiche WebLink
<br />The guide is divided into six broad sections which are summarized <br />below: <br /> <br />A. Information to be Evaluated <br />The following four categories of flood data are recognized: <br />systematic records, historic data, comparison with similar watersheds, <br />and flood estimates from precipitation. How each can be used to define <br />the flood potential is briefly described. <br /> <br />B. Data Assumptions <br />A brief discussion of basic data assumptions is presented as a <br />reminder to those developing flood flow frequency curves to be aware of <br />potential data errors. Natural trends, randomness of events, watershed <br />changes, mixed populations, and reliability of flow estimates are briefly <br />discussed. <br /> <br />C. Determination of the Frequency Curve <br />This section provides the basic guide for determination of the <br />frequency curve. The main thrust is determination of the annual flood <br />series. Procedures are also recommended to convert an annual to partial- <br />duration flood series. <br />The Pearson Type III distribution with log transformation of the <br />flood data (log-Pearson Type III) is recommended as the basic distribution <br />for defining the annual flood series. The method of moments is used to <br />determine the statistical parameters of the distribution from station <br />data. Generalized relationships are used to define the skew coefficient <br />for short-record stations. Methods are proposed for treatment of most <br />flood record problems encountered. Procedures are described for refining <br />the basic curve determined from statistical analysis of the systematic <br />record to incorporate historic flood data, information gained from <br />comparisons with similar watersheds, and flood estimates from precipita- <br />tion. <br /> <br />3 <br />