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February 16, 2012 <br />Project: Inundation Mapping for Farmers High Line Canal and Reservoir Company <br />Vendor: Farmers High Line Canal and Reservoir Company; 725 Malley Drive; Northglenn, CO 80233 <br />Phone: (303) 451-7604 <br />c/o Ms. Cynda Lower <br /> <br />Consultant: Deere & Ault Consulting, Inc.; 600 S. Airport Rd, Building A, Suite 205; Longmont, CO 80503 <br />Phone: (303) 651-1468 <br />c/o Mr. Mark Severin, P.E. <br /> <br />CWCB funding source: Severance Tax Trust Fund Operational Account <br /> <br />SCOPE OF WORK <br /> <br />Deere & Ault Consulting, Inc. (Consultant), at the direction of Farmers High Line Canal and Reservoir <br />Company (Vendor), will perform a dam breach modeling study and flood inundation mapping for the <br />dam at Hyatt Lake. The study shall be in accordance with the latest Breach Guidelines published by the <br />Colorado Dam Safety Branch. The level of analysis shall be “Simple,” as defined in Table 1 of the <br />Guidelines for both the breach modeling and flood inundation mapping. Flood routing models and <br />inundation mapping shall be based on USGS 10-meter Digital Elevation Model (DEM) or best available <br />topographic mapping. Field measurements of bridges and culverts at critical sections shall be <br />incorporated into the model as necessary. The limits of the dam breach flood mapping shall extend <br />from reservoir/dam, downstream to the location where breach flood impacts become negligible. <br /> <br />The downstream limit of the inundation mapping for the dam at Hyatt Lake is expected to extend down <br />an unnamed drainage to Van Bibber Creek and terminate at the confluence with Ralston Creek. <br />Preliminary results will determine if additional modeling is required. <br /> <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 /> <br />PROPOSED METHODOLOGY <br /> <br />The Consultant shall perform a clear day dam failure analysis 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 />for the floodplains shall be based on USGS 10-meter DEMs from the National Elevation Dataset (NED) <br />elevation data.