FLOOD00372

• Designation Number: 294
• County: Boulder
• Community: Unincorporated Boulder County
• Stream Name: North St. Vrain and St. Vrain Creeks
• Title: Floodplain Information Report - North St. Vrain and St. Vrain Creeks
• Date: 12/1/1987
• Designation Date: 1/1/1989
• Floodplain - Doc Type: Floodplain Report/Masterplan

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SECTION 3 - HISTORY OF FLOODING

The flood of May 1894 washed away 20 homes in the lower part of
Lyons. Peak discharge of the 1894 event was later estimated to
be 9,800 cubic feet per second, most of which originated in the
South St. Vrain Creek watershed (References 1,2,3,4,5).

St. Vrain Creek is known to have a long history of floods. Large
floods occurred in 1864, 1876, 1894, 1919, 1941, 1949, 1951,
1957, and 1969. Peak flood discharges and corresponding stages
at Lyons during the period of record are presented in Table 1.

1919 FLOOD

TABLE 1
HISTORICAL FLOOD PEAK DISCHARGES AND STAGES
St. Vrain Creek at Lyons Gage

The July 30, 1919 flood at Lyons washed out all bridges along a
five mile reach on the North St. Vrain immediately upstream of
Lyons. All bridges were also destroyed along a five mile reach
of St. Vrain Creek immediately downtream of Lyons. Water
tranmission mains serving the town of Lyons and Longmont were
also severely damaged, leaving both towns without water. The
roadway up the North St. Vrain was also rendered impassable. The
cloudburst of July 30 was followed by heavy rains on July 31,
1919 and again on August 3, 1919. Several houses and businesses
were flooded more than once during the period of July 31 - August
3. The rains of July 31 washed many bridges out along the South
St. Vrain. Heavy rains in the Big Thompson Canyon on July 31 had
also washed out several bridges. Estes Park was completely
isolated for a time due to the damaged roadways in the Big
Thompson Canyon and the North and South St. Vrain Canyons
(References 1, 2, 3, 4, 5).

(Drainage Area = 212 square miles)

Year

Date

Peak Discharge
(cfs)

Stage
(ft. )

1894 May 31 9,800 8.13
1919 July 30 9,400 7.90
1921 June 2 * *
1938 September 2 8,360 *
1941 June 22 10,500 8.06
1949 June 4 2,970 4.95
1951 August 3 3,920 5.37
1957 May 9 3,060 5.97
1969 May 7 2,900 6.80
* Information not available.

1921 FLOOD

Widespread rains of June 2-7, 1921 caused a flood on the St.
Vrain Creek. Lyons experienced heavy rains during June 4-6, and
both the North and South St. Vrain Creeks carried large volumes
of water. However, little damage occurred near Lyons. Rainfall
was particularly heavy east of the mountains; 5.87 inches of
rainfall were recorded at Longmont for the period of June 2-7.
No estimate of the discharge at Longmont is available, but news
articles state that the Creek was at its highest level in 25
years. The articles also state that the Creek was higher in the
Longmont area than during the flood of 1919. All bridges in
Longmont were reported as destroyed or dangerously near collapse
(References 1, 4, 6).

Following is a compilation of the information available on major
floods affecting the St. Vrain in the vicinity of the study
reach. This information has been compiled from previous
floodplain studies of the St. Vrain. The information from
previous studies was based on newspaper accounts, interviews with
longtime residents of the area, and flow data published in the
U.S. Geological Survey Water Supply Papers and Surface Water
Records.

1938 FLOOD

1894 FLOOD

The floods of June 1864 and May 1976 inundated much valley
farmland and caused severe damage (References 1, 2, 3, 4, 5).

Heavy rains fell east of the mountains within the St. Vrain Creek
basin during the period of September 2-4, 1938. Longmont
reported 4.54 inches of rainfall during this three day period.

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