FLOOD00850

• Designation Number: 31
• County: Arapahoe
• Community: Unincorporated Arapahoe County
• Title: Major Drainageway Planning - Little Dry Creek, Report, Volume I
• Date: 2/1/1974
• Designation Date: 6/1/1974
• Floodplain - Doc Type: Floodplain Report/Masterplan

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would be controlled by detention dams. Their effectiveness in reducing

peak flood flows can be seen readily by comparing peak flood discharges

with and without the dams on Tables 5 and 6.

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The flood detention reservoir areas behind the dams will normally be dry

because large floods are infrequent. These lands, which would be zoned

for flood plain use or would be govenmentally owned, would have a positive

environmental impact since they would provide long term open space and

greenbelt benefits, They may justifiably be called detention parks.

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The proposed five additional detention dams are designed with outlets

of sufficient size to empty each of their full reservoir pools (from

a 100-year frequency flood) in three days, so that the detention capacity

would be available promptly for a possible following flood. The exist-

ing outlet from Englewood Dam would empty the reservoir after a 100-year

flood in 6 to 7 days, and the desirability of modifying its outlet works

to provide more rapid emptying will have to be re-assessed as a part

of the final design of improvements, The five proposed dams are all

earth dams having concrete lined spillways of sufficient size to pass

the probable maximum precipitation flood without endangering the dam.

Spillway crests are set high enough so that the lOO-year frequency flood

will be stored without spillway discharge. The spillway will not operate,

therefore, unless a flood greater than the 100-year frequency flood

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occurs.

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Extensive rehabilitation of Englewood Dam is required to bring it up

to current safety standards. Preliminary design studies indicate that the

dam should be raised, a larger spillway should be provided, and that the

adequacy of the outlet works should be reviewed. Preliminary design of

the rehabilitation of Englewood Dam is shown on Drawing 35.

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Holly Dam is located on Upper Little Dry Creek as shown on Drawing 34,

It is second in importance to Englewood Dam in effecting flood peak

reduction in the lower Little Dry Creek basin.

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