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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The designs that have been developed for Little Dry Creek drainageway

improvements are preliminary. They are considered adequate for esti-

mating overall costs, but they. are not adequate for construction. Cost

estimates herein include allowance for estimated administrative and en-

gineering costs.

Overall Criteria

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The overall design objective is to obtain the most effective flood drain-

age at the least cost while best meeting the flood drainage needs of the

Little Dry Creek basin. This leads to making use of drainage channel types

in the following order of preference: (l) natural channels, (2) grass-

lined channels, (3) concrete-lined channels, and (4) closed concrete con-

duits, Drainage channel size is determined by comparing channel cost with

the cost of upstream flood reducing detention storage, and selecting the

most economical combination. It was found that reducing flood flow peaks

in the lower Little Dry Creek Basin area by providing upstream flood deten-

tion storage is more economical than providing the greater channel capa-

cities required if flood detention storage is not provided. Englewood Dam

and the five proposed flood detention dams are, therefore, essential fea-

tures of the proposed drainageway improvements.

Specific Design Criteria

Specific design criteria adopted for the Little Dry Creek drainage study
are as follows:

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Natural Channels

1. Use natural channels where possible

2. Channel and overbank capacities must be adequate for 100-year

flood with six detention dams.

3. Channel erosion must be minimized.

4. Hydraulic roughness coefficient is that for a reasonably main-

tained presently existing channel.

5. Natural channel area must be in public ownership or designated

as a flood plain area under an enforceable zoning ordinance to

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