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<br />E40 <br /> <br />FLOODS OF 19'65 IN THE UNITED STATES <br /> <br />S~Y OF FLOODS <br /> <br />E41 <br /> <br />caused sigr;ificant floods in the east-central and north-central parts of <br />the State m June. Floods that are considered noteworthy are de- <br />scribed in the order of their occurrence. The east-central floods of May <br />and June were also described by Rennick (1966), <br /> <br />MAY IN EAST-CENTRAL WYOMING <br /> <br />The storm in May in east-central Wyoming was the result of weather <br />patt~r~ that com~ined "0,( the right place at the right time" to produce <br />conditions conducive to heavy precipitation, Moisture-laden air mov- <br />ing into Wyoming from the southwest was raised over cold fronts from <br />the north on May 7 and 13. On May 7 this resuLted in a general storm <br />which started with rain and turned to snow that blanketed the Larami~ <br />Mountains with as much as 32 inches of snow by May 9. Much of the <br />snow ~t.lower e:evations meLted quickly; however, a general snow cover <br />contalllmg 4-6 mches of water equivalent remained at elevations ",bove <br />6,000 fe~t when rain began on May 13. The latter storm, when com- <br />bmed With the snow cover, resulted in an estimated maximum water <br />equi~a~ent of 10 inches in some areas when the flood runoff began. The <br />~reClplt~tl?n I?attern was influenced by orograp)llc factors; the heav- <br />Iest preCipitatIOn occurred on the north side of the Laramie Mountains, <br />and subsequently lighter precipitation fell on the south side. Up to 6 <br />inch~ of precipitation was reported from a "bucket survey" of the area, <br />An lsohyetal map of the storm rainfall for May 13-15 is shown in <br />figure 18. <br /> <br />Typical spring-rwlOff p",tterns were developing when the rains <br />sta,:ted on May 13. The snowfall during the period May 7-9 had <br />"pr1llled the pump," and the rains during May 13-15 produced spectac- <br />ular results. <br /> <br />;Highest runoff occurred on streams flowing from the Laramie Moun- <br />tams (fig, 18) nort~easterly from stations 2-10,12,17,18, and 20 and <br />southerly from statIOns 1 and 23 (table 14), resulting in heavy flood <br />damage on several of the streams, Flooding on Deer Creek inundated <br />many dwellings in the town of Glenrock and oil-well pumps on the <br />flood plain, High water on Box Elder, La Prele, Wagonhound, La <br />Bonte, and Horseshoe Creeks flooded range homes destroyed bridges <br />eroded or deposited sediment on farm lands, and da:naged or destroyed <br />headworks of irrigation ditches. <br /> <br />_ Recurrence intervals for peak discharges on many streams are much <br />ill excess of 50 years (table 14). The peak discharge on Deer Creek <br />(sta. 3), 12,800 cis, was 4_5 times the previous maximum recorded dis- <br />charge, which occul'Tedin 1924. The peak discharge on La Bonte Creek <br /> <br /> <br />105"00' <br /> <br />le MILES <br /> <br />I ~-~"- <br /> <br />EXPLANATION <br />5 <br />Flood-de~ination point <br />Num/Jer cwrespcyn.ds ro <br />t1w.tin to.6we u"and17 <br />-3- <br />Isobyet, showing precipitation <br />in inches, for May 13-15 ' <br /> <br />FIGURE I8.-Location of flood-determination points for May and June and <br />isohyets for May 13---15, floods of May and June in east-central Wyoming. <br /> <br />(sta. 10), 8,770 cis, was 3.2 times the previous maximum recorded dis- <br />charge, which occurred in 1923. The great magnitude of the May floods <br />is graphically represented by figure 19, which compares the discharges <br />at two selected stations w1th previous maximum discharges of record, <br />Three reservoirs on the North Platte River played a major role in <br />preventing flood damage_ Releases from Alcova Reservoir (upstream <br />from the area in fig, 18) and from Glendo Reservoir were decreased <br />sharply on May 14, reducing flood stages along the North Platre River <br />above Guernsey Reservoir, The peak discharge on North Platre River <br />above Glendo Reservoir (sta. 12) was 23,800 cis on May 15, whereas the <br />daily mean discharge below the reservoir was only 1,510 ds. Flood- <br />waters from La Prele Creek were stored in La Prele Reservoir until <br />spilling occul'Ted on May 17_ The peak discharge on La Prele Creek <br />below the reservoir (sta. 8) was only 573 ds on May 20, and above the <br />reservoir (sta. 7) on May 14 it was 7,300 cfs (3,5 times the theoretical <br />50-year flood and 6 times the previous maximum in a 4&-year period <br />ofrecord) , <br />