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<br />North Improvement Area: This alternative will collect the Pawnee Creek overflow and divert these <br />flows directly to the South Platte River in the general vicinity of the Cemetery just south of Sterling. <br />This alternative consists of construction of a benn having an approximate height of 5- feet to the north <br />and west of the Riverside Cemetery. This berm would collect and prevent flows from the Pawnee <br />overflow from entering the City along the HWY 6fRailroad embankments. Included in the alternative <br />is lowering of CR. 24, construction of a channel ",ith a. concrete floodwall, a closure structure for <br />HWY 6, construction of box culverts under the railroad, a siphon for the Sterling No. I Ditch, and <br />construction of a trapezoidal channel to the South Platte River. All :improvements will be sized to <br />handle 5,000 cfs. Flows will overtop the highway, and flow under the railroad in the nl~w culvert. The <br />railroad culverts have been sized such that no increase in the highway depth of flooding will result. <br />Construction of the improvements will include installation of a small storm sewer which will allow <br />draining of a significant ponding area located to the west of the highway and north of the cemetery. <br />The road depression in this area is to allow flows that go around the cemetery to the W(:st to drain back <br />into the proposed improvements. The flood wall and road closure willlbe sized to accommodate three <br />feet of freeboard. <br /> <br />Construction of the channel east of 1he railroad will requin: putting the Sterling No. I Irrigation Canal <br />into a siphon under the channel. This will have the added benefit of limiting flows down the irrigation <br />canal, which currently serves as a conveyance channel for floodwalls into the City of Sterling. Having <br />the siphon will also help prevent canal spillage and bn~ak outs at uncontrolled locations. <br /> <br />The channel will require modifications to two private driveways, and one minor cOlmty road. The <br />modifications will include gradual depressions in the road grades with low flow culvert.~. Road <br />surfaces in the channel bottom will be hardened. This road and driveways will not be accessible during <br />flood events. <br /> <br />At the South Platte River, the channel will drop into the river at a riprap controlled confluence. <br />Detailed mapping of this area is not currently available, bu.t it is anticipated that the bottom of the new <br />channel will be above the IO-year flood stage in the South Platte River. <br /> <br />IlI-24 <br />