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<br />those used In producing PMF's for SEED studies and for other planning studies throughout the
<br />USSR and other USDI agencies,
<br />
<br />Data used to define the PMP (probable maximum precipitation) over the basins studied were
<br />computed uSing the techniques presented in the appropriate HMR (hydrometerological report) [2,
<br />3,4,5,6,7]. The report used is referenced In the discussion section for each flood, The remaining
<br />hydrologic parameters (basin area, stream length, slope, lag coefficient, computed lag time, loss
<br />rate, and selection of a dimensionless unit hydrograph) are also described in the flood discussions,
<br />The unit hydrograph procedure used in this study is discussed in other US8R publications [8, 91
<br />and is not repeated here,
<br />
<br />The term "observed" is used throughout this report in regard to historic flood peaks. In most
<br />cases, no one actually" observed" these floods but, rather, they were estimated on the basis of
<br />postflood measurements,
<br />
<br />SUMMARY
<br />
<br />This study compares estimated PMF peaks with peak floodflows recorded from selected extreme
<br />rainfloods in the 48 conterminous states, Records of peak floodflows from thousands of sites
<br />were available for the data collection phase of the study, Initial data collection efforts produced a
<br />list of approximately 600 of the extreme and more recent events not covered in previous studies
<br />of extreme United States flood peaks. Of these events, 61 were compared with estimated PMF
<br />peaks computed using current US8R data and methodology, All of the floods selected for com-
<br />parison had some field measurements of the flood event and supporting hydraulic computations
<br />to produce the recorded peak flow, A summary of the results is presented in table 1,
<br />
<br />The earliest event studied was the January 1862 flood on the Santa Ana River near Riverside,
<br />California, This flood had a peak flow estimated to be 317,000 hJ/s PMF calculations for this
<br />study produced a peak of 441,200 ftJ/s for a drainage area of 720 mi2 The historic event rep-
<br />resented 72 percent of the PMF peak,
<br />
<br />The most recent event studied was for the Middle Fork of the Little Red River near Shirley, Arkansas,
<br />On December 3, 1982, a flood peak of 241,000 ft3/s was measured for the 302 mi' basin This
<br />flood more than doubled the previous high recorded flood (from nearly 50 years of recordsl The
<br />PMF peak for this site was estimated to be 318,400 h3/s, making the 1982 event 76 percent of
<br />the PMF,
<br />
<br />One of the largest percentages of the PMF in this study was for the Little Nemaha River near
<br />Syracuse, Nebraska. The peak flow at this site occurred on May 9, 1950, It was recorded 3S
<br />225,000 ft3/S for a drainage area of 218 mi' This was over 1,000 ft3/s per ml' for a basin of
<br />over 200 ml' The PMF peak estimated for this site was 277,000 ftJ/s; therefore, the 1950 peaK
<br />represents 81 percent of the PMF,
<br />
<br />2
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