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August 5, 2013 <br /> Project: Inundation Mapping for Platte River Power Authority <br /> Vendor: Platte River Power Authority; 2000 East Horsetooth Road; Fort Collins, CO 80525 <br /> Phone: (970) 229-1756 <br /> c/o Mr. Rocklyn Knutson <br /> Consultant: Smith Geotechnical, Inc.; 1225 Red Cedar Circle, Suite H; Fort Collins,CO 80524 <br /> Phone: (970)490-2620 <br /> c/o Mr. Duane Smith, P.E. <br /> CWCB funding source: Severance Tax Trust Fund Operational Account <br /> SCOPE OF WORK <br /> Smith Geotechnical, Inc. (Consultant), at the direction of the Platte River Power Authority(Vendor),will <br /> perform a dam breach modeling study and flood inundation mapping for a dam within the Vendor's <br /> system.The study shall be in accordance with the latest Breach Guidelines published by the Colorado <br /> Dam Safety Branch.The dam breach level of analysis shall be the "Advanced" method as defined in <br /> Table 1 of the Guidelines for both the breach modeling and flood inundation mapping. Flood routing <br /> models and inundation mapping shall be based on USGS 10-meter Digital Elevation Model (DEM) or best <br /> available topographic mapping. <br /> The dam to be modeled is the Rawhide Dam located at Hamilton Reservoir.The inundation mapping for <br /> Rawhide dam will extend from the dam,down the outlet channel, Coal Creek, Box Elder Creek, Cache la <br /> Poudre River, and to the confluence with the South Platte River.The mapping will then follow the South <br /> Platte downstream to a point where the flood impacts are negligible. Mapping will terminate at or <br /> before the Colorado-Nebraska state line. <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(2011 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 clear day dam failure analysis of the dam and route the resulting outflow <br /> hydrographs downstream using HEC-RAS (or DAMBRK). Breach parameters shall be determined using <br /> empirical equations in accordance with methodologies recommended by the Office of the State <br /> Engineer, Dam Safety Branch. Hydraulic parameters, including width of flow,depth of flow and velocity <br /> at critical locations shall be estimated using the Corps of Engineer's HEC-RAS computer modeling <br /> software. An unsteady-state water surface profile resulting from peak flow rates at various locations <br /> shall be generated.Topographic information for the floodplains shall be based on USGS 10-meter DEMs <br /> from the National Elevation Dataset (NED) elevation data. <br />