FLOOD00920

• County: Mesa
• Community: Collbran
• Stream Name: Plateau Creek
• Title: Plateau Creek Flood Analysis
• Date: 1/1/1984
• Prepared For: Mesa County
• Prepared By: Greenhorne & O'Mara, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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INTRODUCTION

The intended purpose of this study is to review the existing floodplain
informat ion for the Town of Co llbran and a long with supp lementa 1 informati on,
provide a means by which the Town can monitor and prepare for flood flows.
Using this report the Town should be able to identify those areas that would be
subject to innundation during a flooding situation and plan for protection of
those areas by temporary or permanent levees.

DATA

Existing Information

A Flood Insurance Study for the Town of Collbran was published by the
Federal Emergency Management Agency in October 1981 which defines the 100-year
floodplains for Plateau and Grove Creeks within the Town limits. Detailed
hydrologic and hydraulic analyses were carried out to determine the floodplains
for the streams. Also contained in the study is a delineation of the Buzzard
Creek 100-year floodplain which was developed by approximate methods.

Topograhic mapping prepared for the Collbran Sewer District in March 1982
was obtained and is used for the base map in this report. With the high flows
in June of 1983, some channel cutting occurred. The new channel alignment is
shown on the map and is based on aerial photographs taken soon after the peak
flows occurred and on field observations.

Hydrology

A detailed hydrologic analysis was completed as part of the Flood Insurance
Study which established frequency-discharge relationships for the 10-, 50-, 100,
and 500-year floods on Plateau Creek. The 5-year flood discharge was obtained
by extrapolation of the discharge-frequency curves plotted on log-probability
pap er .

A regional stream gage analysis was conducted which took into account the
historic records of several 5tream gaging stations in hydrologically simi lar
watersheds. Peak flows for both snowmelt and rainfall events were analyzed.

Although the intended purpose of Vega Reservoir is not flood control.
according to the Flood Insurance Study. the flows for the 100- and 500-year .
frequency events are estimated to be reduced by 12.5% and 6% at Collbran.

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