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<br />~'..'" <br /> <br />Ex. h,'bir II <br /> <br />Scope of Work <br />Additional Hydraulic Analysis and Section 22 Feasibility Study <br />Cache La Poudre River At Greeley, Colorado <br />November 2002 <br /> <br />Floodplain Manat!ement Services <br /> <br />As part of an effort to develop new flood plain and floodway delineations along the Cache La <br />Poudre River through the City of Greeley and Weld County, the City of Greeley provided the <br />Omaha District with an existing HEC-2 hydraulic model for the river reach between Ash Avenue <br />and 2Sth Avenue. A consulting firm working for the City developed the existing hydraulic <br />model. The Omaha District modified the existing hydraulic model and extended it downstream <br />to the South Platte River and upstream to the vicinity of Windsor. While some modifications <br />were made to the original hydraulic model between Ash Avenue and 2Sth A venue, the original <br />cross section and bridge geometry was mostly unchanged. <br /> <br />During the course of the hydraulic study, the City compared some of the bridge and flood plain <br />geometry between Ash Avenue and 2Sth Avenue with field surveys. Based on a number of <br />discrepancies between the surveys and the hydraulic model geometry, the City decided to obtain <br />new flood plain and bridge cross sections in the Ash Avenue to 2Sth Avenue reach. <br /> <br />Additional cross sections were also to be taken along the East 8th Street overflow area, where <br />cross sections were originally derived from topographic mapping. The Omaha District for the <br />new flood plain cross sections delineated locations. There were approximately 43 new cross <br />sections along the river between Ash Avenue and 2Sth Avenue and six new sections along East <br />8th Street. The new cross sections were obtained using photogrammetric methods. '\ The City <br />obtained new field surveys for seven bridges in the reach. The City also provided surveys for <br />the new foot/horse bridge in Island Grove Park. <br /> <br />Because additional hydraulic modeling using the new surveys was beyond the scope of work in <br />the agreement for the original Cache the Poudre flood plain study between the Corps and the <br />Colorado Water Conservation Board, the following additional work is to be done for the City of <br />Greeley: <br /> <br />The original flood plain cross sections in the reach between Ash Ave and North 2Sth Avenue will <br />be removed and the new cross sections will be added. The bridge data in the hydraulic models <br />will be updated based on the new surveys. The new bridge in Island Grove Park will be added to <br />the hydraulic models. <br /> <br />The Cache La Poudre River channel baseline for the new cross sections resulted in slightly <br />difference cross section stations for the existing cross sections upstream from 2Sth Avenue. The <br />stationing of these cross sections will be adjusted to be consistent with the revised channel <br />baseline. <br /> <br />Revised 10-, SO-, 100-, and SOO-year Cache La Poudre flood water surface profiles will be <br />computed and plotted. For the overflow reach along East 8th Avenue, profiles will be computed <br />for flood events that result in significant overflows into the area. The 100-year and SOO-year <br />flood boundaries previously delineated will be adjusted as necessary. <br /> <br />1 <br /> <br />