FLOOD09590

• County: Arapahoe
• Community: Aurora
• Stream Name: Cherry Creek Lake
• Basin: South Platte
• Title: Hydrologic Improvement Assessment Cherry Creek Lake
• Date: 9/1/1993
• Prepared For: State of Colorado
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Project

combination with the existing dam and spillway (without modification); with the
existing spillway blocked; and with a combination of dam raises along with the
existing spillway or with the existing spillway blocked.

ALTERNATIVE 2 - CHUTE SPILLWAY

A typical plan, section and profile of Alternative 2, is shown on plate 32.

This spillway alternative would be constructed through the dam and would consist

of a reinforced concrete approach slab, ogee weir, spillway chute, stilling

basin, and side walls. With a crest elevation of 5600 feet m.s.l., the spillway

would be founded essentially on compacted embankment materials and natural

foundation soils. The stilling basin and lower end of the chute would be in the

Denver Formation which consists of soft claystones, siltstones, and sandstones.

The concrete approach slab and chute would be 2 feet thick and the stilling basin

slab would be 4 feet thick, The chute and approach slab would be underlain by

2 feet of frost blanket. The slabs would be anchored to the foundation

materials with anchors which consist of "einforcing bar in grouted holes. 40 feet

deep and spaced at 8 feet between anchors. Walls would attain stem heights of

from 35 to 70 feet. A two-lane bridge would be required over the spillway for

traffic on the embankment crest. Because of the large walls, bridge piers and

relatively weak foundation, this alternative has been designed with steel piling

foundation under the higher walls. The piling would be driven into the Denver

Formation. Drainage behind the walls would consist of p.V.c. pipe surrounded by

filter materials. Slab drainage would consist of a similar pipe and gravel

system spaced at ISO-foot intervals.

The design weir coefficients ranged from C - 3.1 for low heads to C - 3.9

for the design head. The estimated effect of the bridge piers on the spillway

discharge was based on the effective crest length.

This alternative is located entirely on Government land. Additional lands

for construction, operation, maintenance, and flowage easements would not be

required for this alternative.

As shown in table 14, the least costly option for Alternative 2 would be 2a

at $38.8 million while the most costly option would be 2h at $62.3 million.

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