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Stagecoach Road Reconstruction <br /> May 19, 2017 <br /> lying south of Stagecoach Road. However, there is no mapped floodplain associated with the <br /> culvert at Sta. 51+13. <br /> The culvert at Sta. 23+75 will be upsized from a 36 in. dia. CMP to a 49 in. X 33 in. arch CMP, and <br /> will be buried 4 inches beneath the existing flowline. Similar to the Black Earth Creek crossing, <br /> the proposed overtopping elevation of the roadway will not be increased in this location. In order <br /> to ensure that the proposed culvert is at least hydraulically equivalent to the existing culvert, <br /> MSA compared the hydraulic conveyance capacities of the existing and proposed culverts over a <br /> wide range of flow conditions,the results of which are summarized below. <br /> Table 1—Flood Elevation Comparison <br /> Existing Culvert Proposed Culvert <br /> Size: 36 in. dia. CMP Size: 49 in. X 33 in. Arch-CMP (4 in. bury) <br /> Cross Sectional Area: 7.07 SQ FT Cross Sectional Area (with bury): 8.04 SQ FT <br /> Length: 50 FT Length: 59 FT <br /> Upstream Invert: 894.95 Upstream Invert: 894.62 <br /> Downstream Invert: 894.34 Downstream Invert: 894.10 <br /> Roadway Overtop Elevation: 898.50 Roadway Overtop Elevation: 898.50 <br /> Flow Rate (CFS) Stage Flbw Rate (CFS) Stage <br /> 10 896.38 10 895.90 <br /> 20 897.08 20 896.48 <br /> 30 897.70 30 897.04 <br /> 40 898.38 40 897.67 <br /> 45 898.58* 45 898.30 <br /> 50 898.65* 50 898.55* <br /> 60 898.75* 60 898.68* <br /> Note: *indicates roadway overtopping <br /> As summarized above,for all conditions the proposed culvert replacement results in a reduction <br /> in the upstream flood elevation,thus satisfying the requirement for"no rise". <br /> In addition to the floodplain zoning permit, the project requires the following permits: <br /> • WDNR NOI permit for construction site disturbance over one acre. <br /> • WDNR and USACE permits for wetland disturbance. <br /> • WDNR permit for municipal culvert replacement on a navigable waterway. <br /> • Dane County shoreland erosion control and stormwater management permits. <br /> All of the above permits are currently in the review process with the exception of USACE review, <br /> which is complete. A copy of the USACE's confirmation letter is attached. <br /> Page 2 of 2 8913001_floodplain_permit_memo <br />