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<br />. <br />1.., <br /> <br />l <br /> <br />l <br /> <br />l <br /> <br />l <br /> <br />l <br /> <br />I <br /> <br />1 <br /> <br />t <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />Based on the HEC-2 model prepared by the SCS, the existing chal11lel through the bridges falls <br />approximately 1.9 feet from an elevation of 3980.0 upsll'eam of HW'f 6 to an elevation of 3978. I <br />downstream of the UPRR. In order to limit the extent of the bridge widening at HWY 6. the proposed <br />channel through the bridges will be lowered about 1.5 feet. The proposed channel lowering will <br />require a drop structure upstream ofHWY 6. <br /> <br />ldeally, the excess material generated from the major channel improvements in the vicinity ofHWY 6 <br />and the UPRR. in addition to the low flow channel further downstream. would be used to construct the <br />north and south levees. However, the material must be tested to determine if its physical properties <br />will achieve the goals of a flood control levee. <br /> <br />Two additional levees are required upstream of HWY 6 to eliminate the Pa\\nee Creek overflows. <br />Levee Number 2 will begin at HWY 6 and generally continue west to a point about 400 feet west of <br />CR. 35. From there the levee will turn north and tie into a natural high point approximately 1,000 feet <br />to the north. A gravel driveway along the 1,000 feet reach will need to be raise.:} about 3 feet to allow <br />access to a residence west of CR. 35. The overall length of Levee Number 2 ",'ill be about 3,760 feet <br />and it will range in heighr from 1 foot to 5 feet. <br /> <br />Levee Number 3 will begin at a natural high point 1,200 feet west of CR. 35 and continue for about <br />5.240 feet due west to a point about l,200 feet west of CR. 33. The levee will range in height from I <br />foot to 5.5 feet. According to the existing HEC-2 model, the 100-year warer surf,lce elevation <br />upstream of CR. 33 for both existing and proposed conditions is 4009. This water surface elevation is <br />equal to the elevation of CR. 33 at the intersection with the gravel driveway located 500 feet north of <br />Pawnee Creek. Therefore, CR. 33 will have to be raised 10 elevation 4012 1:0 provide .3 feet of <br />freeboard during the 100-year event. The road raise will begin about 100 feet north of the gravel <br />driveway and continue south for about 500 feet to a point where CR. 33 is at elevation 4012. Levee <br />Number 3 will be located on the north side of a residence near CR. 33 leaving several structures on the <br />channel side of the levee. However. based on spot elevations from the mapping, it does not appear <br />that the structures are within the 1 DO-year residual floodplain. <br /> <br />Finally, three ring levees will be required to protect individual residences \vhich are currently located <br />in the I DO-year floodplain. The ring levees will have milder slopes along the landward side so they <br />will be less noticeable to the homeowners. As an alternative to the full height ring levees. a <br />combination ring levee and floodwall could be used to minimize the height of the levees surrounding <br />the residential structures. The flood wall would be 3 feet tall itnd made of 6" X 6" tongue and groove <br />timbers. Typical cross-sections of both the standard levees and the ring levees are shown on Figures <br />12 and 13. <br /> <br />In the summer of 1996 the UPRR completed the improvements to their bridge to meet the proposed <br />I DO-year flow conditions. However, the UPRR constructed the bridge over the exis:ing chal11lel cross- <br />secrion so that the area under the new bridge is not increased until the channel improvements proposed <br />in this study are completed. Costs have been included in the estimate for the chatmel improvements <br />and for soil cement erosion protection under the new railroad bridge. <br /> <br />37 <br />