FLOOD04288

• County: Boulder
• Community: Lyons
• Stream Name: St. Vrain and North St. Vrain
• Basin: South Platte
• Title: North St. Vrain and St. Vrain Floodplain Update
• Date: 6/1/1998
• Prepared For: Lyons
• Prepared By: BRW, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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North St. Vrain & St. Vrain Creeks
Floodplain Update

Town of Lyons

1949 FLOOD

Nearly 3 inches of rain which fill in the 51. Vrain valley on June 4, 1949 caused the 51. Vrain to
peak at 2,970 cfs at Lyons. Peak discharge reached approximately 6,700 cfs at Longmont. All
bridges between Longmont and Lyons were either impassable or under close watch by State4
Highway Department crews, while two bridges were destroyed entirely. Thirty-five people
were evacuated from the 51. Vrain floodplain. The road in the South 51. Vrain canyon was
closed as a precautionary measure. The Burlington Northern Railroad track to Lyons was also
rendered useless as floodwaters had destroyed the roadbed east of Lyons (References 1, 2, 3, 5,
6).

1951 FLOOD

Heavy rains occurred in the St. Vrain basin during the afternoon and night of August 3,1951.
Lyons received 6.3 inches from a cloudburst which began about 6 p.m. Flooding resulted along
the South 51. Vrain, and along the reach from Lyons to the mouth of the 51. Vrain. Floodwaters
destroyed several sections of road in the South 51. Vrain Canyon and inundated businesses in
Lyons.

Railroad and highway bridges near Longmont were also damaged. Farmers in the valley
between Lyons and the mouth of the 51. Vrain suffered crop losses as well (References 1,2, 3, 5,
6).

1957 FLOOD

Three to five inches of rain fell on the entire 51. Vrain basin during the night of May 8-9, 1957.
The 51. Vrain at Lyons peaked at 3,060 cfs about 1 pm on May 9, while the Str. Vrain at the
mouth peaked at 9,450 cfs at 12:15 am on May 10. Two bridges were destroyed, approaches to
several bridges were washed out, and several irrigation diversion structures were damaged or
destroyed (References 1,2, 3,4, 6).

1969 FLOOD

Heavy rainfall combined with snowmelt to cause prolonged high flows on the 51. Vrain. The
worst flooding occurred on May 7-8, and June 15-21, 1969. Roads and bridges along the stream
were extensively damaged, streambanks eroded, and farmlands flooded. The peak discharge at
Lyons was 2,900 cfs on May 7. Peak discharge at the4 mouth was 10,300 cfs on May 8
(References 1, 2, 3, 4, 6).

Following are selected newspaper headlines and articles dealing with several of the major
floods along the St, Vrain. These newspaper accounts were taken from the Camp, Dresser,
MeKee, Inc. report (Reference 5) and from the Water Resources Consultants, Inc. report
(Reference 4). The Colorado Water Conservation Board and Boulder County supplied the
historical photographs.

Floodplain Information Report 11
K:1356DOlOO4\FLOODPLAIN INFORMATION REPORT.doc

June 1998