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Last modified
1/26/2010 10:12:05 AM
Creation date
10/5/2006 4:55:40 AM
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Title
Guidelines for Determining Flood Flow Frequency Bulletin 17A
Date
3/1/1977
Prepared By
USWRC
Floodplain - Doc Type
Educational/Technical/Reference Information
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<br />normally be neglected in flood flow frequency analysis. Peak flow <br />estimates of historic floods can be substantially in error because of the <br />uncertainty in both stage and stage-discharge relationships. <br />At times errors will be apparent or suspected. If substantial, the <br />errors should be brought to the attention of the data collecting agency <br />with supporting evidence and a request for a corrected value. A more <br />complete discussion of sources of error in streamflow measurement is <br />found in (7). <br /> <br />V. Determination of Frequency Curve <br /> <br />A. Series Selection <br />Flood events can be analyzed using either annual or partial-duration <br />series. The annual flood series is based on the maximum flood peak for <br />each year. A partial-duration series is obtained by taking all flood <br />peaks equal to or grea ter than a predefi ned base flood. <br /> <br />If more than one flood per year must be considered, a partial- <br />duration series may be appropriate. The base is selected to assure that <br />all events of interest are evaluated including at least one event per <br />time period. A major problem encountered when using a partial-duration <br />series is to define flood events to ensure that all events are independent. <br />It is common practice to establish an empirical basis for separating <br />flood events. The basis for separation will depend upon the investigator <br />and the intended use. No specific guidelines are recommended for defining <br />flood events to be included in a partial series. <br />A study (8) was made to determine if a consistent relationship <br />existed between the annual and partial series which could be used to <br />convert from the annual to the partial-duration series. Based on this <br />study as summarized in Appendix 14, the Work,Group recommends that the <br />partial-duration series be developed from Dbs~ved data. An alternative <br />but less desirable solution is to convert from the annual to the partial- <br />duration series. For this, the first choice is to use a conversion <br />factor specifically developed for the hydrologic region in which the <br /> <br />8 <br />
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