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<br />40
<br />
<br />FLOODS IN COLORADO
<br />
<br />As these were cloudburst floods, the peak discharges were of short
<br />duration.
<br />The widespread rains of June 2-7,1921, caused a flood on St. Vrain
<br />Creek, reported as follows in the Lyons Recorder, of June 9, 1921:
<br />
<br />While Lyons experienced an extraordinary heavy rain during June 4-6, and
<br />both St. Vrain Creeks {North and South] carried large volumes of water, very
<br />little damage was done. We were very fortunate that very little water fell up
<br />either canyon, the rise coming from rains in the Longs Peak region and the natural
<br />melting of mountain snow.
<br />
<br />The peak discharge recorded at Lyons was 2,020 second-feet,
<br />June 7, The rainfall was particularly heavy east of the monntains,
<br />as shown by the 5.87 inches recorded ot l.ongmont, June 2-7. ~o
<br />estimate of the discharge at Longmont is available, but a dispatch to
<br />the Boulder Camera, June 7,1921, stated:
<br />
<br />The St. Vrain Creek here is way out of its banks and is said by people who
<br />should know to be the highest in 25 years [evidently referring to the flood of 1894].
<br />The Creek is carrying more water a.nd is higher in this region than during the
<br />cloudbursts at l.yons 2 years ago. The Creek at this point is three-quarters of a
<br />mile wide. Water is up to the Farmers' Mill and the depot. All bridges in the
<br />oity are Qut or dangerous.
<br />The storm of September 2-4, 1938, was fclt in the St. Vrnin
<br />Creek Basin chiefly east of the mountains, as the peak discharge at
<br />the Lyons gaging station, which occurred at 1 n. m., September 3,
<br />was only 1,650 second-feet. At LOnl,'rrlOnt the precipitation for the
<br />3-day period was 4.54 inches, and at Fort Lupton 3.99 inches. J3clow
<br />Lyons the discharge increased rapidly, owing to run-off from tributary
<br />streams, some of which are ordinarily dry gulches. Boulder Creck
<br />enters St. Vrain Creek 6 miles east of Longmont, and at that point
<br />the flood was increased by th~ peak discharge of 4,410 second-feet
<br />from Boulder Creek. The peak at the mouth of Boulder Creek
<br />occurred at noon September 3. Ten miles farther downstream, as
<br />measured along the valley, the peak discharge at the gnging station
<br />near the mouth of St. Vrain Creek was 8,360 second-feet at 6 p. m.,
<br />September 3, as shown by a slope-area measurcment made by L. T.
<br />Burgess, chief hydrographer of the State of Colorado. Lefthand
<br />Creek enters St. Vrain Creek three-quarOOrs of 11 mile below Longmant;
<br />its peak discharge was 812 second-feet at 11 p. m., September 2, and
<br />at the time of the peak on St. Vrain Creek the flow from Lefthand
<br />Creek was about 400 second-feet. To show the comparative discharges
<br />during the flood, the mean daily discharge, in second-feet, at the
<br />various gaging stations is presented in the following table.
<br />
<br />.
<br />
<br />MAJOR FLOODS-SOUTH PLATTE RIVER
<br />
<br />41
<br />
<br />Daily di8charge, in second-feet, in St. Vrain Creek Basin, Sept. 2-9, 1938
<br />
<br /> September
<br />Gaging station
<br /> 2 2 , 5 6 7 8 .
<br /> - -
<br />St. Vrl\in Creek at LYODS___._.____n "" 1,370 818 872 451 362 331 27.
<br />Leflhaud Creek at mouth, at Long. "'2
<br />monL________________.____________ 148 188 123 81 83 56 "
<br />DGulder Crook at mouth, near Long-
<br />mont____________.____________.____ 160 ~300 1,630 1,020 '" '" 331l 366
<br />St, Vra.ln Creek at mouth, near
<br />PllltteviUc___._____..___......_____, 374 3,200 5,300 2,t110 2,340 1,600 1,100 '"
<br />
<br />Below the mouth of Boulder Creek the bottomlands along St. Vrain
<br />Creek were overflowed to a considerable extent.
<br />
<br />LEFTHARD OREEK
<br />
<br />Lcfthand Creek enters St. V rain Creek a short distanee below
<br />Longmont. The only flood of definite record is that caused by the
<br />heavy mins of May 29-June 1, 1894, when 6.80 inches was reported
<br />at Ward, located on the headwaters at an elevation of 9,200 fret.
<br />Heferring to this flood, the Boulder Camera, June 2, 1894, staOOs:
<br />
<br />From Boston Mill to Ward tha.t little strea.m is a howling river. The railroad
<br />bridges and all wagon .bridges over Lefthand Creek were washed OUt4 Lefthand
<br />Creek hi 300 yards wide a mile from Niwot [on the plains}. Old timers stated
<br />that this is the worst flood since 1864. '
<br />
<br />BOULDER CREEK
<br />
<br />Boulder Creek drains the Front Ran~e, nnd its fan for a distnnee
<br />of 10 miles upstream from Boulder is 229 fect per mile. Between
<br />Boulder and the mouth of the creek the drainage area is a part. of the
<br />ph,ins, where the fall in the 22 miles from the edge of the plains to
<br />the mouth is 26 feet per mile.
<br />
<br />Gaging stations on Boulder Creek
<br />
<br />Station
<br />
<br />Drainago
<br />aroa. ~squllrc
<br />mlies)
<br />
<br />Period of record
<br />
<br />NCl1r OrodeIL_________.____._____
<br />Ncar noulder___n_h_'-_______"'_
<br />At mouth, near LongmonL._u___
<br />
<br />105 Aup;ust 1887 to October 1888; March 1007 to Novemoor
<br />1u14; February 1916 to date.
<br />134 April 1888 to October 1892; May 1895 to Decemb~r
<br />1001; July 1904 to December 1908.
<br />512 March 1927 to date.
<br />
<br />D \lJ'ing the periods of known floods on Boulder Creek no gagin!1:
<br />station was in operation, and the information available consists chiefly
<br />of extracts from the press, with no estimate of discharge except for
<br />the flood of May 31, 1894, a study of which was made some years
<br />later by a firm of consulting engineers.
<br />
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