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<br />. The most critical data sets are the systematic discharge record at Fair Oaks <br />and the associated set of annual maximum three-day rain-flood discharge (corrected <br />for upstream reservoirs). Based on several analyses, including one that relied on a <br />series of three-day estimates of basin-average precipitation, the latter data set appears <br />to be reasonably homogeneous and the apparent increase in the frequency of large <br />flows that it exhibits since 1950 is real. <br />. The three-day mean of the 1862 flood (estimated to be 265,000 cfs) is <br />likely the largest peak discharge on the American River since 1848 (and perhaps <br />since the beginning of the 19th century). This historical information should be used <br />in American River frequency analysis, although there are questions about its <br />accuracy and about its relevance given the potential hydrologic impacts of hydraulic <br />gold mining. <br />. Although the quality of the paleoflood information developed by the U.S. <br />Bureau of Reclamation is excellent, it has two problems. First, explicit use of this <br />information in flood frequency requires the assumption that floods are independent <br />and identically distributed in time or the use of a particular non-independent and <br />identically distributed model. Existing paleoclimatic data call into question the <br />assumption, but are not yet of sufficient quality to allow development of such <br />models. Second, the USBR paleoflood information does not include any information <br />about paleofloods of the magnitudes of greatest interest---discharges with <br />exceedance probabilities from 0.5 up to and beyond 0.002. For these reasons, the use <br />of the USBR paleoflood information was approached with caution. <br />. Meyer's envelope curve of maximum flood discharges is not especially <br />useful to American River frequency analysis. <br />. The two most recent PMF estimates for the American River at Folsom <br />Dam represent reasonable upper bounds on the three-day flood quantile associated <br />with a probability of at most I x 10-3. <br /> <br />- <br /> <br />38 <br /> <br />Improving American River Flood Frequency Analyses <br /> <br />