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<br />Issue: What are the accepted methods and where do they applv? <br /> <br />5,7 Paleohydrology Concepts <br />Paleohydrology is the scientific study of past or ancient flood events which occurred prior to <br />established record keeping methods or documentation by other human records. Paleohydrologic <br />information enhances short-term streamflow. records by decreasing the uncertainty of f1ood- <br />frequency estimates and is particularly useful for providing information in ungaged drainage <br />basins, Paleoflood data indicate the probable upper limits of the largest floods that hav€: occurred <br />in river basins. the occurrence and non-occurrence of paleohydrologic evidence of floods, such <br />as flood bars, alluvial fans, and tree scars, provide valuable hydrologic information about the <br />number, magnitude, age, frequency and spatial occulTence of floods, <br /> <br />The method employs the evaluation of geological, biological, and physical evidence within a <br />stream basin to determine the flood history of the basin. The limitations with this method <br />include changes in the dimensions and depth of the paleochannel over time, any man-made <br />alterations to the basin which alter morphological characteristics, inferences made in the field can <br />result in excessive margins of error, It is difficult to use paleohydrology principles for the <br />establishment of flood frequency values; however, paleohydrology has a practical application for <br />the--determination of the ranges for large design discharges, <br />Policy statement: Paleohydrology is not to be used as a sole source of hydrologic <br />information in flood frequency analysis for the lO-year to tOO-year flood discharges. <br />Paleohydrolgy should ouly be used as a confirmation of large historic flood events. <br /> <br />\chp5jan,mtg <br /> <br />.. <br /> <br />8 <br />