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 storm sewers were generally placed with a minimum cover of 2-feet to

minimize the traffic loading impacts on the pipe, Storm sewer sizes and

locations were also determined, in part, to minimally impact existing utili-

ties and to utilize existing storm sewer facilities where practical,

), DENVER HIGHLINE CANAL SPILL STRUCTURE

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Capacity of inlets were determined from the Criteria Manual. Storm sewer

inlets were sized based upon the Colorado Department of Highways type-R curb

opening inlets with 6-inch throat and 5-, 10-, and 15-foot lengths, The capa-

city of the inlet depended upon whether the inlet was in a sump or on-grade

condition, For inlets on-grade, the design capacity was also based upon the

estimated street grade, Typical values of design capacity used for preliminary

design are listed in the following table:

The criteria for the design of this structure was based upon the Denver

Highline Canal Master Plan (Reference-8), The spillway was designed to dis-

charge 550 cis under 100-year flood conditions, The crest elevation has been set

I,I-feet above the water surface at the base flow discharge of 200 cfs, The

crest should be concrete and have cut-off walls for erosion protection, Addi-

tionally, the crest should be designed so as not to restrict access along the

canal road. Adequate protection upstream and downstream of the crest should

also be provided.

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4 , OPEN CHANNEL

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INLET SIZE CONDITION CAPACITY
5 L.F, Sump 4.0
10 L,F, Sump 8,0
15 L,F, Sump 12,0
5 L.F. On-Grade ),0
10 L.F, On-Grade 5.5
15 L,F. On-Grade 7.0
2, CALEY DETENTION FACILITY

Design of the channel in Reach-B was based upon conveying the upstream

storm sewer flow to the downstream storm sewer reach. Using a Manning "n" of

.028, the 100-year channel velocities were limited to 7.0-feet per second.

The concrete channel bottom should be a minimum of 5.0-feet wide and the grass-

lined channel side slopes should be 4: 1 maximum,

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C. Construction Sequence

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Caley detention was sized with a maximum embankment height less than 15-

feet and with the maximum depth at the emergency spillway less than 10-feet.

The final construction plans will therefore not require approval of the State

Engineer's Office (SED), However, due to the proximity to downstream residences,

the facility should be designed to meet SED criteria, The facility was planned

to take advantage of topographical conditions, land use, and multi-purpose

useage, The spillway width of 100-feet was sized for a storm intensity approx-

imately half way between a 100-year and PMP event, The design discharge is

2600 cfs compared to a peak 100-year inflow of 1010 cfs. The 4:1 embankment

slopes will improve the visual imapct and add to stability. The final design

should be coordinated with the South Suburban Metro Recreation and Park District

to assure the maximum recreational and flood protection benefits.

Improvements for Reaches-A, -B, and -C are somewhat dependent on the proposed

detention facility in Reach-D, Priority of construction can be related to the

damage frequency, net benefits, or other criteria established by the municipality,

Based upon these criteria and the fact that 80% of the total average annual damages

occur in Reach-A, the immediate priority should be construction of the proposed

storm sewer system in Reach-A, Without Caley detention. the proposed system would

be capable of handling a flood with a frequency of about 2-year, With construction

of the detention facility above Caley Avenue, the second priority, the capacity of

the storm sewer in a Reach-A will be increased to a 5-year frequency level, Con-

struction of Caley detention facility would also eliminate most of the flood damages

in Reach-C by intercepting all flooding from the drainage basin above, The outlet

pipe, beneath the dam would be constructed to discharge at street level, After the

storm sewer system 1S constructed along South Pennsylvania Avenue, the outlet works

can be modified to discharge directly into the storm sewer, thereby eliminating

discharges in the street.

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