|
<br />miles of the Front Range and foothills from Boulder to Fort Collins, Unofficial reports indicated 6,3 inches of
<br />precipitation occurred near Lyons and more than 6 inches occurred southwest of Niwot A flood peak
<br />determination of 5,700 cfs on Dry Creek was obtained about 1,5 miles south of Niwot The crest of the flood
<br />occurred about 9:50 p,m, on 3 August The flood swept across l),S, Highway 287, 2 miles south of Longmont,
<br />at about 10:45 p,m, The flood on Dry Creek, which was 1/4 miles wide in places, swept away crops, buildings,
<br />and equipment and required the evacuation of about 50 people, Railroad and highway embankments and
<br />bridges were washed out
<br />
<br />Flood of Mav 1969, Heavy rainfall WITh a relatively long duration occurred from 4 May until 8 May, The storm
<br />covered an area along and near the eastern slopes of the Rocky Mountains and extended into portions of the
<br />high plains, The hea~est amounts were centered 25 miles southwest of Denver and extended in a band along
<br />the foothills of the Rocky Mountains northward of Estes Park, Rainfall amounts of 7,60 inches were reported
<br />at Boulder.
<br />
<br />Flood of May 1973, Rainfall generally ranging to as much as 6 inches fell on the plains east of the Rocky
<br />Mountains beginning on 5 May, The Dry Creek basin received amounts ranging from 2 to 4 inches, Runoff
<br />from this general storm contributed to considerable flooding on the South Platte River,
<br />
<br />4,1.11 ST. VRAIN CREEK
<br />
<br />Flood History, Early records of floods are fragmented ancllacking in detail. Flooding occurrErd on St Vrain
<br />Creek in 1864, 1876, t894, 1921, 1938, 1941, 1949, 1%1, 1957, and 1969,
<br />
<br />Flood of June 1864, A storm in June 1864 resulted in a flood, the effects of which reportedly "were felt
<br />severely" in the St Vrain valley,
<br />
<br />Flood of May 1876, The Golden, Colorado Tribune 01 May 31,1876 described a flood during that month
<br />as covering farmlands from "bluff to bluff" at the junction of St Vrain and Left Hand Creeks, at Longmont
<br />
<br />Flood of 31 May 1894, The flood of 31 May 1894 washed away 20 homes at Lyons, "A day or two before
<br />Memorial Day in 1894, a steady rain began to fall which soon reached flood proportions, and the entire lower
<br />part of the town was washed away, No lives were lost, , ," This flood had an estimated peak discharge of
<br />9,800 cubic feet per second (cis) at Lyons, a flood of SUCll magnitude as to have less than a 1 -in,(IO chance
<br />of occurrence in any year. South St Vrain Creek contributed the greater part of the flood,
<br />
<br />Flood 30-31 Julv 1919, In late July 1919, a series of severe thunderstorms caused flash flooding along St
<br />Vrain Creek, From the Lyons Recorder dated 2 August 19'19:
<br />"The heaviest and most destructive cloudburst. , ,in the memory of the oldest inhabitant visited Lyons on
<br />Wednesday (July 30) between 2:30 and 3:45 p.m, It took out all the bridges on the North St Vrain for about 5
<br />miles up and 5 miles downstream, The Longmont and Lyons water mains up the canyon were torn out in many
<br />places, , , miles of road were torn out along the narrow canyon, The people living along the banks of the river
<br />were flooded out, and many abandoned their homes for higher ground and safety, , . homes (in the lower part
<br />of town)", were in a roaring sea of water 2 and 3 feet deep,"
<br />Another crest on the following day again flooded houses in the lower areas of town and washed out :300 yards
<br />of railroad track east of Lyons, The peak discharge on 30 July was later computed to be 9,400 cis, The right
<br />bank of North St Vrain Creek was flooded to a width of 300 feet
<br />
<br />Colorado Flood
<br />Hydrology Manual
<br />
<br />4.13
<br />
<br />DRAFT
<br />
|