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<br />. <br /> <br />. <br /> <br />Task 4 - Proposed (Alternative) Solutions: <br />The, Contractor shall formulate and evaluate at least 3 alternative plans to address the flood <br />problem component of a Project for the Pawnee Creek Channel Conveyance and Pawnee Creek <br />Overflow, Generally, the area for flood analysis (for the purposes of this Scope of Work) <br />includes the stream reach which extends from County Road 25 to the junction of the Pioneer <br />Ditch and Highway 138, <br /> <br />Alternative 1 shall be the "no action" alternative, <br /> <br />Alternative 2 shall address the proposal as presented in the report entitled "City of Sterling <br />Drainage and Flood Control Implementation Plan" dated June 1997. <br /> <br />Alternate 3 shall be the upstream reservoir proposal as presented in the report entitled "Flood <br />Plain Management Study, Pawnee Creek and Logan Creek, Colorado" dated April 1992, and its <br />supplement. <br /> <br />Alternate 4 shall be the Pawnee Creek overflow side channel at the Riverside Cemetery as <br />proposed in the CWCB Conceptual Flood Hazard Mitigation Plan, dated September 1997, <br /> <br />Alternate 5 shall be the same as Alternate 4 with a 25 to 50-year flood control conveyance <br />channel on the mainstem of Pawnee Creek in the vicinity of the community of Atwood. <br /> <br />Alternate 6 shall be a non-structural proposal which will provide flood mitigation benefits <br />throughout the study reach. <br /> <br />Enl!ineerinl! Investil!ation for Task 4 <br /> <br />. Hydrology Analysis - The Contractor shall use the existing hydrology as approved and <br />designated by the CWCB and adopted by the local sponsors. <br /> <br />. Hydraulic Determinations - The Contractor shall perform hydraulic investigations to <br />determine water surface elevations for feasibility and preliminary design and study, The <br />water surface elevations shall use the existing base flood elevations (IOO-year). The analysis <br />shall be performed to a detail that will insure the feasibility of proposed project <br />implementation. If a project proposal is recommended on the Pawnee Creek mainstem in the <br />vicinity of Atwood, Colorado, a hydraulic analysis shall be performed in insure that the flood <br />hazard is not increased due to project implementation. <br /> <br />After the selection of a project alternative, the contractor shall make a hydraulic <br />determination which will demonstrate a correlation of the impact of the July 30-31, 1997 <br />flood event on the project features/elements. <br /> <br />. Floodplain Mapping - The Contractor shall present a pre-project (existing flood inundation <br />area) and post-project residual 1 DO-year floodplain map, The Contractor may present the <br />July 30-31,1997 flood mapping as prepared by the CWCB, <br /> <br />Task 5 - Description of Proposed Project: <br />The Contractor, Local Sponsors, and the CWCB shall mutually agree upon the local flood <br />protection alternative that will be recommended as part of the proposed project. The Contractor <br /> <br />4 <br />