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I I I ,I I II I I I I I I II I I I I I I I I -;,;- 28 Street is also Colorado Highway 263, the City should request the Colorado Department of Highways to place the structure in their improvement plan. Improvements also need to be made to the 6th Avenue crossing of the river. Three improvements were considered, namely (1) replacement of the bridge with a structure capable of passing the 100-year flood, (2) removal of the bridge, and (3) maintaining the existing bridge and providing an overflow roadway sec- tion. Either removal or replacement of the existing bridge will result in a better hydraulic section by eliminating the backwater condition created by flood overtopping of the existing bridge. Maintaining the existing bridge requires the use of flood control berms on the north and south side of the river. The total length of the berm is about 1,000 feet. This section bet- ween berms would be established as a floodway and no building improvements would be allowed. The floodway section includes property within the City on the south side of the river and property within Weld County on the north side of the river. This study investigated the flood control aspects of the bridges. Before any selection of bridge alternatives is made, additional analysis regarding transportation needs should be completed. The structural integrity of the bridges also should be investigated to determine the feasibility of enlarging the existing structures. Dredging to increase channel capacity will not solve flooding problems and will create additional flooding and sedimentation problems downstream of the City. All improvement alternatives (with the exception of maintaining the existing condition) require the replacement or enlargement of the 8th Street, 5th Street, and 6th Avenue bridges, and the relocation of the Great Western Sugar Company intake structure. Riprap protection is required at all outside channel bends. All alternatives, with the exception of the combination chan- nel, require the trapping of sediment upstream of Greeley using an existing gravel pit or continued dredging. The improvement alternatives require the use of berms at the upstream study limit to guide flood flow into the improved channel. The improvement alternatives are depicted schematically in Figure 7 through 18.