FLOOD02374

• Designation Number: 343
• County: Gunnison
• Community: Crested Butte
• Stream Name: Coal Creek
• Basin: Gunnison
• Title: Floodplain Information Report - Report for Coal Creek: Crested Butte, Colorado
• Date: 9/1/1992
• Designation Date: 3/1/1993
• Floodplain - Doc Type: Floodplain Report/Masterplan

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II. COAL CREEK BASIN DESCRIPTION

Coal Creek through Crested Butte, Colorado is located approximately 30 miles
north of Gunnison, Colorado in Gunnison County. Sheet 1 of 10 (following the text
of this report) delineates the Coal Creek drainage basin boundary. Coal Creek
headwaters originate in the Elk Mountains, approximately 10 miles west of Crested
Butte. The Coal Creek basin study area contains approximately 21 square miles
of mountainous terrain ranging in elevation from 8,880 to 12,207 feet above mean
sea level. Major tributaries of Coal Creek include Elk Creek, Splains Gulch, and
Wildcat Creek.

Coal Creek flows easterly through a canyon composed mainly of shale material.
Native vegetation consists of willow and box elder along the canyon. Coal Creek
enters Crested Butte from the southwest and angles through the western portion
of Town in a north-easterly direction as shown on sheet 2 of 10. At its confluence
lies the Slate River. Copies of the Federal Emergency Management Agency "Flood
Insurance Rate Map", for the Slate River floodplain delineation, have been included
in the rear of this report. Within the Town limits of Crested Butte, Coal Creek is
bridged by five roads, six pedestrian bridges, and one building deck.

III. HYDROLOGIC ANALYSIS

Flood flows on Coal Creek are caused primarily by rapid melting of the snowpack
during the months of May and June of each year. The high water problems that
the Town experienced in 1978 and 1979 were the result of snow melt from a heavy
snowpack according to Mr. Larry Lang. During May and June of each year,
precipitation is generally observed to be low at most stations within the Gunnison
River Basin. Convective type thunderstorms occur extensively over the Gunnison
River Basin during the summer months. The extent of these thunderstorms is
small and they do not cause peak flows in Coal Creek at Crested Butte.

The hydrology developed for the 1976 study was based on two recognized
methods. The first method was a regression equation developed by the U.S.G.S.,
and the second method was a U.S. Soil Conservation Service curve number
method. Stream flow records available at the time for Coal Creek included the
period 1943-1946, as measured at a location upstream of the Town of Crested
Butte.

Three hydrologic methods were utilized in this study to develop the proper
hydrology for Coal Creek. Each of the three hydrologic methods studied is
explained below, along with the results of each hydrologic analysis. Included in
the Technical Appendix, under separate cover, are the detailed computations of
the three hydrologic methods.

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