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<br />SOUTh. rLAT'T'E RIVER BASIN, COLORADO, JUNE 1965
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<br />from Dem'er, to its mouth at North Platte, Nebr. The flood runoff from
<br />Pawnee Creek caused some flooding near Sterling on ~TuIle 15-16. The
<br />most damaging flooding was in the Denver metropolitan area the night
<br />of June 16. This flood was generally within banks downstream from
<br />the vicinity of Greeley. The Bijou Creek flood of June 18 entered the
<br />South Platte Riyer aud caused most of the damage at Fort :.\rorgan
<br />and do"rnstream. The crest frOI11 Plum Creek passed the rnouth of
<br />Bijou Creek about 35 hours later.
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<br />ACKXOWLEDG:\IEXTS
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<br />The data in this report were coilccted as part of the cooperative pro-
<br />grams established bet,yeen the u.S. Geological Sur\"{~y and other Fed-
<br />eral, State, county, and municipal ag-C'l1cies. The data were collected
<br />and compiled under the supel'Yision of J.'W. Odell, Colorado district
<br />engineer of the Surface 'Vater Branch, ""Vater Resources Division. The
<br />field snr'"eys and some computations ,yere coordinated DJ H. F.
<br />Matthai, regional hydraulic specialist. Office computations were di-
<br />rected by C. T. Jenkins and R. J. Snipes. Experienced Inea from two
<br />other districts assisted ,yj t h field sl.U"1;eY5.
<br />The U.S. '\Yeather Bureau, the 1~.8. _I.rmy Corps of Engineers, and
<br />the U.S. Bureau of Reclamation furnished meteorological information
<br />precipitation, flood damage, and flood inundation data, and isohyetal
<br />maps. Their cooperation is gratefully acknowledged.
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<br />RELATIVE MAGNITUDE OF THE FLOODS
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<br />Both lay people and hydrologists h,,,'e used one or more yardsticks
<br />or criteria to evaluate the relative 111agnitude of a flood. These range
<br />from the informal, but neyertheless \-alid, designation of "gully-
<br />washer" to "the maximum probable flood." Three criteria are used
<br />in this report: comparisons with maximum floods known and com-
<br />parisons by frequency relations and channel conditions.
<br />
<br />COMPARISON WITH MAXHIUM FLOODS KNOWX
<br />
<br />Hoyt and Langbein (1955) plotted maximum discharges kno\m in
<br />the L"nited States in 1890 and in WoO against drainage area. They
<br />pointed out that in the 60 years between 1890 and 1950, "the upper limit
<br />of our knowledge on floods has been pushed up abont ten fold for very
<br />small drainage basins, and abont >threefold for large streams." Though
<br />they cnlled their curve an enyelopin:r cun"c, it is only 1l00ninally so, as
<br />they chose to draw it below six discharges shown on their graph.
<br />The writer has found records of fiye more floods that plot above
<br />Tfoyt. nnd Langbein's ct!rn~" Three af them huye occurred since 1950.
<br />An averaj!ecurve (curve A, fig. 2) thl'OUgh the 11 high points is higher
<br />~21 0--00-2
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