C153916 Contract - Laserfiche WebLink

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. . . Surveys - Additional ground surveys will be needed in the area of the U.S. Highway 85 bypass and along the East 8th Street overflow to supplement existing information. The City of Greeley has agreed to provide the necessary surveys. Hydrology - Thepeak discharges used in the FPMS study were from the 1988 revision to the Cache La Poudre River hydrology. This hydrology was accepted by the CWCB and was to be used in future studies on the Cache La Poudre River. Hydraulics - For the FPMS study, 10-, 50-, 100-, and 500-year existing conditions water surface profiles were developed. A one-foot rise floodway was also developed. The baseline hydraulics from the FPMS study will be revised using new surveys ofthe U.S. Highway 85 bypass north of East 8th Street in the split flow computations. The split flow computations in the FPMS study used elevation information from 2 foot contour mapping. The Cache La Poudre main channel flood boundaries and floodway will be revised, if necessary. The water surface profiles for the 8th Street split flows will be recomputed using the split flow discharges computed using the new baseline hydraulics. A revised floodway will be computed along East 8th Street. For the floodway analysis, the East 8th Street roadway and ditches will be considered as "the stream channel". The revised floodway alignment will be adjusted, where possible to try to meet the City's concerns. It is possible that the average depths of the 8th Street overflow for the 1 OO-year flood will average from 2 to 3 feet, which would meet the requirements for an AH shallow flooding zone designation. FEMA may not require a floodway in an AH Zone. Mapping - The mapping for this study will be prepared using the City of Greeley's GIS mapping system. The flood boundaries and floodway delineation from the Corps FPMS study were added to the GIS by the City to produce flood boundary and floodway maps. Some revisions to the flood boundaries and floodway delineation may be needed following the adjustments to the hydraulic analyses. Features specific to FEMA mapping such as Base Flood Elevations and Flood Insurance Zones will be annotated to hard copy maps and furnished to the City to revise the GIS mapping. Draft maps produced from the GIS will be reviewed and revised if necessary before the final hardcopy and electronic versions are submitted. Scales for hardcopy maps will follow those used on the existing Flood Insurance Rate Maps (FIRMs). The elevation datum for the revision will be ihe National Geodetic Vertical Datum of 1929, which was used for the City's GIS mapping Coordination - Significant coordination activities will be required with the City and County so ensure that the communities accept the study results. The draft study results will be furnished to the CWCB for review and comments. The Corps, as the study contractor, will attend and participate in intermediate and final meetings to present the preliminary and final FIRMs to the City and County. 2