FLOOD03629

• County: Boulder
• Community: Boulder County
• Stream Name: St. Vrain Canyon Upstream of Lyons
• Basin: South Platte
• Title: Floodplain Information Report
• Date: 10/1/1978
• Prepared For: Boulder County
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Therefore, upon official approval of this report by the Colorado Water

Conservation Board, the areas described as being inundated by the 100-

year flood (Intermediate Regional Flood)l can be designated as flood

hazard areas and their use regulated accordingly by the local agencies.

Aerial photography and contour mapping were provided by the Colorado

Water Conservation Board and prepared by Bell Mapping Company of Denver,

Colorado, October 1977. The contour interval on all mapping was two-

feet with a one-inch equal to 100-feet horizontal scale, llaps can be

obtained from Boulder County,

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Purpose and Scope

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Related Flood Studies

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This report was prepared to guide local officials in planning the use

and regulation of the floodplain areas such that flood hazards and fu-

ture damages are eliminated or minimized. It includes information on

historical floods, existing factors which influence the flood hazard,

and the nature and extent of probable future floods,

A floodplain information report that included 1.5 miles of South St,

Vrain Creek at Lyons was prepared by the Army Corps of Engineers in

1972 (Reference 4), In that report, the 100-year flood water surface

profile for the South St, Vrain Creek reach is one to three feet higher

than the 100-year flood profile developed in the present study. Dis-

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The report data includes flooded area maps delineating the 100-year

flood boundary, flood profiles and floodplain cross sections showing

the high water elevations for the 10-, 50-, 100- and sOO-year floods at

selected reference points. A supplement to this report in the form of

a technical addendum includes the supporting engineering and hydrologic

data which may further be used in engineering studies in the location

and design of roads, bridges and channel modifications,

cuss ions with the Corps of Engineers

surface profile was computed using a

estimated. In addition, the earlier

channel and floodplain conditions.

verified that the earlier water

higher discharge, which was over-

profile was based on 1971 stream

Since the water surface profile in

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the present study results from a more accurate discharge and reflects

existing field conditions (1977), it super cedes the water surface pro-

file in the previous Corps of Engineers' report.

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Acknowledgements

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The assistance and cooperation of the below listed agencies and organ-

izations in addition to numerous private citizens in suppling informa-

tion and data are appreciated and gratefully acknowledged.

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U.S, Department of the Interior, Geological Survey
U,S. Department of the Army, Omaha District, Corps of Engineers
Colorado Water Conservation Board
Colorado Division of Water Resources
Boulder County Public Works Department

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IThe terms "Intermediate Regional Flood", "lOO-year flood", and "one
percent flood" can be used interchangeably as they are all defined by
the same type of flood event (see Glossary), However, to avoid con-
fusion, the term "lOO-year flood" will be used exclusively throughout
this report.

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