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

I
I
I
I
I
I

5. Cutoff trenches and toe drains are included to increase dam
embankment stability.
6. Faces of the dams are sodded to reduce rainfall erosion and to
improve their appearance.

I
I
I
I
I
I
I
I
I
I
I
I
I

Drop Structures and Energy Dissipators

Drop structures are used to reduce flow velocities in natural and

grass-lined channels. The drop structures lower the water surface

and dissipate its energy to reduce channel erosion that would other-

wise occur. Emergency spillways and the lower ends of culverts having

high exit velocities are provided with energy dissipating structures

and downstream channel riprap.

Bridges

Bridges are designed to pass the lOO-year flood flow with the six
flood detention dams in operation.

Culverts

Culverts are designed in accordance with U.S. Department of Commerce,

Bureau of Public Roads Hydraulic Engineering Circulars Nos. 5 and 10.

Corrugated steel pipe, reinforced concrete pipe, or reinforced con-

crete box culverts are used as shown on the preliminary plans, depend-

ing on local conditions. Energy dissipators are used at culvert out-

lets where exit flow velocities exceed allowable downstream channel

velocities in order to minimize erosion.

Highline Canal and City Ditch

The Highline Canal crosses Little Dry Creek, Greenwood Gulch, Black-

mer Gulch and Quincy Gulch as shown on Chart 2, page ll. The ex-

isting Highline Canal crossing of Little Dry Creek is adequate to pass

lOO-year flood flows. The City Ditch crossing of Little Dry Creek is also

adequate to pass lOO-year flood flows. It is proposed to carry City

Ditch across Greenwood Gulch when it is channelized in a new flume.

-53-