FLOOD02223

• County: Arapahoe
• Community: Littleton
• Stream Name: Upper Slaughterhouse Gulch
• Basin: South Platte
• Title: Major Drainageway Planning
• Date: 3/1/1983
• Prepared For: Littleton, Arapahoe County
• Prepared By: UDFCD
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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The recommended plan in the Phase-A report consisted of S-year storm sewer,

along the drainageway alignment, Due to the erratic alignment of the drainage-

way in this reach, the selected alignment is more cost effective and will im-

prove the collection of the local runoff in the street, A majority of the

flood damage reduction for this reach, however, is due to the proposed Caley

detention pond site (Reach-D), One of the main purposes for the sewer in this

reach is to provide for the outfall from Caley detention site.

controlled spill area for the Denver Highline Canal thereby improving the

canal storm carrying capacity downstream and reducing the flood damages,

Construction of this facility should not be undertaken until the Caley deten-

tion facility has been completed,

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As part of the selected drainage improvements for this reach, the consul-

tant was directed to prepare Phase-B design drawings for a collector system

from Clarkson Street to Pennsylvania Street to connect to the sewer in Reach-C.

The collector system addresses the drainage problems located in the sump area

along Clarkson Street near Oakwood Avenue.

S, REACH-E (Denver Highline Canal to Euclid Avenue)

The selected alternative in this reach is construction of a S-year storm

sewer system. Problems along this reach are caused by an inadequate existing

storm sewer, The existing IS-inch pipe in Downing Street is fed by a 24-inch

and 48-inch pipe in East Arapahoe Road. Damage in the reach is the inundation

of the residences lining the floodplain. Damages are mainly comprised of

structure and content damage and interrupted traffic,

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4, REACH-D (Caley Avenue to the Denver Highline Canal)

The selected alternative for Reach-D is construction of a lOa-year detention

facility, Problems in this area are caused by a poorly defined channel across

an improved open area (Southwood Park) and the unimproved area occupied by the

KBRQ radio station transmitter, The potential flood damages in this reach are

erosion, debris removal, structure and content damage to the radio station

transmitter building, and possible revenue loss caused by lost radio air time,

B, Design Criteria

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The criteria used for the preliminary design of the improvements was obtained

from the Urban Storm Drainage Criteria Manual (Reference-S), and the requirements

of the City of Littleton and Arapahoe County, Specifically, criteria used for

preliminary design for this Phase-B study is as follows:

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}, STORM SEWERS

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Construction of this alternative would require relocation of the radio

station transmitter, but would allow for recreational use within the reservoir

area. As previously mentioned, the majority of benefits due to this alternative

will be derived in the lower reaches of the study, The damages for all frequency

storms are substantially reduced in Reach-C, The damages in Reach-A with

Caley detention will be essentially eliminated for the S-year flood. The Reach-

A IOO-year with Caley detention will be approximately equal to the present

damages for a S-year flood. Peak lOa-year inflows into Powers Park are reduced

such that overtopping of the embankment will not occur,

The design of the storm sewer system was based upon the entire flows in the
reach of the drainageway for the selected design frequency, In some areas, 1n
order to intercept the design flows, local collector systems outside of the

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major drainageway were required. These local systems were also sized and costed

utilizing the same criteria as for the main system, Details of the required

local collector systems are also shown on the drawings,

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Also as part of the selected alternative in Reach-D, is construction of a

side channel spill structure on the Denver Highline Canal. This structure has

been designed in accordance with the criteria and concepts set forth in the

Denver Highline Canal Master Plan (Reference-8). The structure will provide a

For Phase-B preliminary design, all storm sewers were sized using precast

reinforced concrete pipe (RCP) flow hydrualics, with a Mannings coefficient

value (n) of 0.012, Where practical, the elevation of the crown of the pipe

was set to match the hydraulic grade line. In some areas, the pipe will operate

under pressure for the design flows. Manholes were included in the system at

alignment, grade, and size changes in pipe, Special manhole shaping should be

utilized at the changes in alignment of the storm sewer to reduce junction losses,

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