FLOOD04012

• Designation Number: 184
• County: Jefferson
• Community: Unincorporated Jefferson County
• Stream Name: Bear Cree, Mt. Vernon Creek, Sawmill Gulch, etc.
• Basin: South Platte
• Title: Flood Hazard Area Delineation - Southern Jefferson County
• Date: 12/1/1981
• Designation Date: 2/5/1982
• Floodplain - Doc Type: Floodplain Report/Masterplan

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slope of the streambed is 1 percent for the reach studied near Tiny

Town and 3 percent for the reach upstream of Bear Creek Reservoir;

therefore, supercritical velocities will occur on most of the reaches

studied. Development is still minimal along the reaches studied.

storms (cloudbursts). Many lives have been lost and excessive

property damage has occurred as a result of flooding along the more

developed reaches of Bear Creek and Mount Vernon Creek. Some of the

more destructive floods which have occurred along the various study

reaches are briefly described below, additional information can be

found in References I, 2, and 3:

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Parmalee Gulch, a left bank tributary of Turkey Creek, drains 6

square miles surrounding the Indian Hills residential area. Parmalee

Gulch originates in the vicinity of Bear Mountain and flows in an

easterly direction toward Turkey Creek. Elevations in the drainage

basin range from 6800 feet to over 8600 feet (MSL). The average slope

of the streambed is over 3 percent and supercritical velocities will

occur on the entire reach. The presence of residential development in

the floodplain and numerous undersized crossings creates flooding

hazards along the reach studied.

- Bear Creek

Flood of July 24, 1896: This flood was the result of a 24-hour

general rain which terminated in a cloudburst on Cub Creek, a

tributary of Bear Creek. The peak flow at the Morrison gaging

station above the mouth of Mt. Vernon Creek was computed to be

8,600 cfs, the highest flow recorded at this gage.

Flood of July 7,1933: This flood was the result of a cloudburst

in the vicinity of Idledale, The peak flow at the Morrison

gaging station was computed to be 8,110 cfs.

Flood of September 2, 1938: This flood was the result of a

cloudburst centered on the divide between Bear Creek and Mt.

Vernon Creek in the area of Genesee Mountain (also refer to

subsequent section on Mt. Vernon Creek). The precipitation from

this storm was estimated to be over 8 inches in two hours with 4

inches falling in the most intense half-hour. The peak flow

recorded at the Idledale gaging station was 4,620 cfs, and the

peak flow recorded at the Morrison gaging station was 6,200 cfs,

Other Floods: Other floods of lesser magnitude have occurred on

the study reaches of Bear Creek covered in this report in the

years 1876, 1894, 1934, 1941, and 1969,

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Deer Creek, a left bank tributary of the South Platte River, has

its headwaters east of Conifer in Jefferson County. Deer Creek flows

in an easterly direction to meet the South Platte River in Chatfield

Reservoir. Elevations in the drainage basin range from 5500 feet to

over 9000 feet (MSL). The basin has an area of 22 square miles at the

upstream end of the study reach and approximately 32 square miles

above Chatfield Reservoir, The average slope of the streambed is

approximately 3 percent but the downstream end of the reach has a

milder slope with a wide floodplain which is subject to shallow

flooding. Supercritical velocities occur mainly in the reach above

the hogback. Development in the floodplain is still limited,

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FLOOD HISTORY

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Floods along the Front Range of Colorado can be caused by general

rains, localized thunderstorms, snowmelt, rain on snow, or combina-

tions of these basic precipitation types, On the stream reaches

studied in this report, floods have been produced in all of these

ways. However, the majority of the recorded floods, and all of the

most severe floods, have been produced by localized, intense thunder-

- Mount Vernon Creek

Flood of September 2, 1938: This flood (also refer to preceding

section on Bear Creek) produced an estimated peak flow of 3,900

cfs two miles upstream of Morrison and a peak flow of 9,230 cfs

at half a mile above the mouth of Mt. Vernon Creek in Morrison.

The destruction caused by this flood was compounded since the

peak flows from Bear Creek and Mt. Vernon Creek arrived at their

confluence virtually simultaneously.

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