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February 16, 2012 <br /> Project: Inundation Mapping for the Colorado River District <br /> Vendor: Colorado River District.; P.O. Box 1120, Glenwood Springs, CO 81602 <br /> Phone: (970) 945-8522 <br /> c/o Mr. Ray Tenney, P.E. <br /> Consultant: W. W.Wheeler and Associates, Inc.; 3700 South Inca Street; Englewood, CO 80110 <br /> Phone: (303) 761-4130 <br /> c/o Mr.Stephen Jamieson, P.E. <br /> CWCB funding source: Severance Tax Trust Fund Operational Account <br /> SCOPE OF WORK <br /> W. W.Wheeler and Associates, Inc. (Consultant), at the direction of the Colorado Water District <br /> (Vendor), will perform a dam breach modeling study and flood inundation mapping for Ritschard Dam. <br /> The study shall be in accordance with the latest Breach Guidelines published by the Colorado Dam <br /> Safety Branch. The level of analysis shall be "Simple," as defined in Table 1 of the Guidelines for both <br /> the breach modeling and flood inundation mapping. Flood routing models and inundation mapping <br /> shall be based on USGS 10-meter Digital Elevation Model (DEM) or best available topographic mapping. <br /> Field measurements of bridges and culverts at critical sections shall be incorporated into the model as <br /> necessary. The limits of the dam breach flood mapping shall extend from reservoir/dam, downstream <br /> to the location where breach flood impacts become negligible. <br /> The downstream limit of the inundation mapping for Ritschard Dam is expected to extend downstream <br /> to a point along the Colorado River. The location of that point will be determined in the preliminary <br /> analysis. <br /> The inundation limits shall be prepared in UTM coordinates(NAD 83, Zone 13—meters)which shall be <br /> overlaid on base mapping that includes color aerial imagery(2009 or newer). The inundation map shall <br /> be printed in color on a minimum sheet size of 11"x 17". The inundation extents shall be clearly <br /> illustrated and include peak discharge estimates, peak flood wave arrival times and peak flood wave <br /> depths at critical locations. Roads, highways and critical infrastructure (schools, hospitals,fire stations, <br /> etc.) shall be annotated and any roads expected to be overtopped by the flood wave shall be identified. <br /> The map shall include a legend noting the dam, DAMID, north arrow and a graphic scale. <br /> PROPOSED METHODOLOGY <br /> The Consultant shall perform a dam failure analysis based on a maximum reservoir water surface <br /> associated with a Probable Maximum Flood (PMF) of the dam and route the resulting outflow <br /> hydrographs downstream using HEC-HMS. Breach parameters shall be estimated in accordance with <br /> methodologies recommended by the Office of the State Engineer, Dam Safety Branch. Hydraulic <br /> parameters, including width of flow, depth of flow and velocity at critical locations shall be estimated <br /> using the Corps of Engineer's HEC-RAS computer modeling software. A steady-state water surface <br /> profile resulting from peak flow rates at various locations shall be generated. Topographic information <br />