FLOOD09102

• County: Logan
• Community: Sterling
• Basin: South Patte
• Title: Sterling Flood Control Interceptor Channel Project
• Date: 4/1/2002
• Prepared For: Sterling
• Prepared By: URS
• Floodplain - Doc Type: Project

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SECTIIITWO

Alternatives Considered

Alternative 3 -Improve Routing of Pawnee Creek Flood Flows

This alternative was identified as Alternative 4 in the applicant's Flood Hazard Mitigation
Feasibility Study (ICON 1998). All components of the alternative would be sized to handle
5,000 cfs of flood flows (projected 100-year flood event). This alternative would have no effect
(adverse or beneficial) on flooding within Atwood and would provide quite limited flood control
within rural Logan County. Specific project features are shown in Exhibit 8 and are described
below.

. Construction of a 1,500-foot-long by 50-foot-wide by 5-foot-high berm to the north and east
ofthe Riverside Cemetery.

. Lowering a 300-foot section and raising an 800-foot section ofCR 24.

. Construction of a 500-foot-long by 75-foot-wide channel with a concrete floodwall north of
the cemetery; the floodwall would be sized to allow 3 feet of freeboard, which means the top
of the floodwall would be 3 feet higher than the elevation of the 100-year flood event.

. Building and installation of a closure structure for Highway 6 that is sized to accommodate
3 feet of freeboard. The closure structure would include manholes that, when opened, would
allow the installation of vertical I-beams which would serve as tracks for the placement of
wooden planks ("stop logs") to contain and transport the floodwater across Highway 6. This
structure would include a stop log structure upstream and downstream of the actual crossing
point. The temporary closure structure would be erected only when flooding in the vicinity
of Riverside Cemetery was predicted.

. Construction of eleven 20-foot by 4-foot box culverts under the UPRR embankment.

. Installation of a siphon under the new flood channel for the Sterling No. I Ditch.

. Construction of a 7,000-foot-long by 250-foot-wide flood channel from the UPRR
embankment to the South Platte River.

. Modification of two private drives and one minor county road by creating gradual depression
in road grade within the constructed channel, hardening the road surface within the
constructed channel, and installation of a low-flow culvert within each road grade to convey
low flows across the county road and two driveways,

. Construction of a riprap-protected drop structure where the constructed flood flow channel
discharges to the South Platte River. The discharge structure would affect approximately
450 linear feet of the South Platte River's stream bank.

Photographs of the proposed location of the flood channel and the UPRR embankment at the
Riverside Cemetery location are provided in Exhibits 9 and 10.

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