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I I I I I I I I I I I I I I I I I I I 6 PLANS OF IMPROVEMENT Three fl God control alternatives were developed as follows: 1. Alternative 1 would eliminate overflows into the South Fork from floods of the magnitude experienced in 1989. All bridges would be replaced with modern structures of adequate capacity and channel improvements made between (a) County Road 19 and the U.S. Hi9hway 6 Bridge and (b) between the Burlington Northern Bridge and County Road 21. County Road 21 would be raised and the east-west county road just north of the railroad would be raised to contain flood flows between County Roads 21 and 23. Soil excavated from the channel reach above County Road 21 would be used for road improvements. Fi9ure 2 shows the proposed improved channel cross-section just upstream from Highway 6. Figure 3 shows the improved channel cross- section between the railroad bridge and County Road 21. Table 1 summarize<s hydraulic design features of roads, bridges, and channels under Alternative 1. Fi9ure 4 shows the proposed new elevation of County Road 21 across the North Fork floodplain north of the Burlington Northern Railroad. Figure 5 shows the improved flow line profile of the North Fork in the reach between County Roads 19 and 21. Flood Flows would be contained by the east-west county road between Roads 21 and 23. A dike approximately 2 feet high around the farmstead at the north end of cross-section 7 would prevent expected sheet slow from entering this area. 2. Alternative 2 would include the channel and road improvements of Alternative 1. Rather than rep1acin9 the U.S. Highway 6 and Burlington Northern bridges, the discharge capacity of these structures would be increased from approximated1y 3,500 c.f.s. to perhaps 7,QOO c.f.s. (including overflows) by enlarging the waterway areas between the existing abutments and improving the flowline profile as shown in fi9ure 6. County Road 21 south of U.S. 6 would also be improved by filling in the existing overflow channels and providing a spillway to route overflows around the south edge of the town; An outflow channel approximately 1,200 feet long would be constructed below the spillway. A levee would also be constructed on the north side of the channel and extended a sufficient distance beyond the channel to prevent backwater from entering the town. Fi9ure 6 shows a cross section of the existin9 road and proposed improvements. The , , ~ , r>" r> ..... _ ., , _., _ I. _., _, _ .1