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<br />North SI. Vrain & St. Vrain Creeks
<br />Floodplain Update
<br />
<br />North St. Vrain & St. Vrain Creeks
<br />Floodplain Update
<br />
<br />Town of Lyons
<br />
<br />Town of Lyons
<br />
<br />SECTION 3 - HISTORY OF FLOODING
<br />
<br />1919 FLOOD
<br />
<br />St. Vrain Creek is known to have a long history of floods. Large floods occurred in 1864, 1876,
<br />1894,1919,1941, 1949, 1951, 1957, and 1969. Peak flood discharges and corresponding stages at
<br />Lyons during the period of record are presented in Table 2.
<br />
<br />The July 30, 1919 flood at Lyons washed out all bridges along a five mile reach on the North St.
<br />Vrain immediately upstream of Lyons. All bridges were also destroyed along a five mile reach
<br />of St. Vrain Creek immediately downstream of Lyons. Water transmission mains serving the
<br />town of Lyons and Longmont were also severely damaged, leaving both towns without water.
<br />The roadway up the North St. Vrain was also rendered impassable. The cloudburst of July 30
<br />was followed by heavy rains on July 31, 1919 and again on August 3, 1919. Several houses and
<br />businesses were flooded more than once during the period of July 31 - August 3. The rains of
<br />July 31 washed many bridges out along the South St. Vrain. Heavy rains in the Big Thompson
<br />Canyon on July 31 had also washed out several bridges. Estes Park was completely isolated for
<br />a time due to the damaged roadways in the Big Thompson Canyon and the North and South St.
<br />Vrain Canyons (References 1, 2, 3,4,5).
<br />
<br />TABLE 2
<br />HISTORICAL FLOOD PEAK DISCHARGES AND STATES
<br />St. Vrain Creel< at Lyons Gage
<br />
<br />(Drainage Area = 212 square miles)
<br />
<br />Year
<br />1894
<br />1919
<br />1921
<br />1938
<br />1941
<br />1949
<br />1951
<br />1957
<br />1969
<br />1995
<br />
<br />Peak Discharge
<br />(cfs)
<br />9,800
<br />9,400
<br />2,050
<br />8,360
<br />10,500
<br />2,970
<br />3,920
<br />3,060
<br />2,900
<br />4,200
<br />
<br />1938 FLOOD
<br />
<br />Stage
<br />(ft.)
<br />8.13
<br />7.90
<br />
<br />1921 FLOOD
<br />
<br />Date
<br />May 31
<br />July 30
<br />June 7
<br />September 2
<br />June 22
<br />June 4
<br />August 3
<br />May 9
<br />May 7
<br />May 29
<br />
<br />Widespread rains of June 2-7, 1921 caused a flood on the St. Vrain Creek. Lyons experienced
<br />heavy rains during June 4-6, and both the North and South St. Vrain Creeks carried large
<br />volumes of water. However, little damage occurred near Lyons. Rainfall was particularly
<br />heavy east of the mountains; 5.87 inches of rainfall were recorded at Longmont for the period of
<br />June 2-7. No estimate of the discharge at Longmont is available, but news articles state that the
<br />Creek was at its highest level in 25 years. The articles also state that the Creek was higher in the
<br />Longmont area than during the flood of 1919. All bridges in Longmont were reported as
<br />d4stroyed or dangerously near collapse (References 1, 4, 6).
<br />
<br />.
<br />
<br />.
<br />
<br />8.06
<br />4.95
<br />5.37
<br />5.97
<br />6.80
<br />7.85
<br />
<br />. Information not available.
<br />
<br />Heavy rains fell east of the mountains within the St. Vrain Creek basin during the period of
<br />September 2-4, 1938. Longmont reported 4.54 inches of rainfall during this three day period.
<br />
<br />The peak discharge of the St. Vrain at Lyons was 1650 cfs at 1:00 AM on September 3, while the
<br />peak discharge at the mouth of the 51. Vrain was estimated as 8,360 cfs at 6:00 PM the same day.
<br />Newspaper reports indicated that "scores" of families along the St. Vrain in the Longmont area
<br />were forced from their homes along the Creek by the high water. Two bridges on State
<br />Highway 52 were also washed out and the bridge approaches damaged (Reference 4).
<br />
<br />Following is a compilation of the information available on major floods affecting the St. Vrain in
<br />the vicinity of the study reach. This information has been compiled from previous floodplain
<br />studies of the St. Vrain. The information from previous studies was based on newspaper
<br />accounts, interviews with longtime residents of the are, and flow data published in the u.s.
<br />Geological Survey Water Supply Papers and Surface Water Records.
<br />
<br />1894 FLOOD
<br />
<br />The floods of June 1864 and May 1976 inundated much valley farmland and caused severe
<br />damage (References 1, 2, 3, 4, 5).
<br />
<br />1941 FLOOD
<br />
<br />The flood of May 1894 washed away 20 homes in the lower part of Lyons. Peak discharge of the
<br />1894 event was later estimated to be 9,800 cubic feet per second, most of which originated in the
<br />South St. Vrain Creek watershed (References 1, 2, 3, 4, 5).
<br />
<br />Cloudbursts occurred over both North and South St. Vrain Creeks on June 22, 1941. Peak
<br />discharge at Lyons was estimated as 10,500 cfs. A resident of Longmont was killed at his cabin
<br />in South St. Vrain Canyon by the flood. Three homes in the canyon were destroyed, and several
<br />homes in Lyons were flooded. Damage was reported to the roads in both North and South St.
<br />Vrain Canyons. The road damage, in conjunction with a bridge washout, caused the road in the
<br />South St. Vrain Canyon to be closed for several days. The "swinging bridge" in Lyons was also
<br />destroyed by the floodwaters (References 1,2, 3, 4, 5, 6).
<br />
<br />Floodplain Infonna/ion Report 10
<br />K:\35600\004\FLOODPLAIN INFORMATION REPORT.doc
<br />
<br />Floodplain Information Report 9
<br />K:\356QO\004\R.OODPLAIN INFORMATION REPORT.doc
<br />
<br />June 1998
<br />
<br />June 1998
<br />
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