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<br />03/27/1995 13:11 <br /> <br />7192753051 <br /> <br />HRM <br /> <br />PAGE 02 <br /> <br />Ms. Honey R. Moschetti <br /> <br />-2- <br /> <br />February 6, 1995 <br /> <br />outlined below should be acceptable to the SEO. However, some modification to the scope might <br />be required if the SEO in Denver has a different position regarding appropriate analysis methods <br />and procedures. <br /> <br />Task 1 - Data Review. GEl will review and collect available eXlstmg data, including <br />information presented in the 1980 Phase I Inspection Report for DeWeese Dam, soil classification <br />and land use data for the watershed above the dam, available USDA Natural Resources <br />Conservation Service (fonnerly SCS) or U.S. Forest Service aerial photographs of the <br />downstream floodplain. and USGS 7.5 minute quadrangle mapping. <br /> <br />Task 2 . 50 Percent PMF Development and Preliminary IDA. We will perform a preliminary <br />evaluation of the potential benefits of the IDA and identify critical downstream cross sections <br />where more detailed infonnation will be required.. The prelimin3l}' evaluation will include <br />development of the SO percent PMF (using 50 percent of the PMP) inflow flood based on <br />Hydrometeorological Report 5'SA (HMR55A). This inflow flood will.be used, to perform dam- <br />break analysis and downstream channel routing from the dam to a location inunediately <br />downstream from Canon City.. The dam-break analysis and channel routing will be perfonned <br />using the U..S.. Army Corps of Engineers' (COE) HEC-l computer program. Water surface <br />profiles wiIJ be developed with the COE HEC-2 program.. A minimal level of cross sectional <br />data will be obtained at representative locations from USGS 7.S minute quadrangle maps. <br /> <br />If our preliminary evaluation clearly indicates that the IDA will not result in a subslantia1 <br />reduction of the required inflow design flood, we will immediately advise the Reservoir Company <br />of our findings. If the Reservoir Company wishes to terminate the IDA analyses based on our <br />preliminary evaluation, we will prepare a brief letter report summarizing our preliminary <br />analyses, results, and recommendations. <br /> <br />If the preliminary analysis indicates that the IDF can be reduced below the 50 percent PMP level, <br />a more rigorous IDA analysis will be required for SEO approval. We will meet with Mr. Graber <br />and representatives of the SEO dam safety branch in Denver to review the preliminary results <br />and confirm analysis assumptions and requirements for SEO review and approval of the more <br />stringent analysis. <br /> <br />Task 3 · Incremental Damage Analysis. The IDA will be used to develop the inflow design <br />flood for DeWeese Dam.. The analysis will require development of appropriate stream geometry <br />in the study area, which will be an expansion and refinement of the cross section data developed <br />during Task 2.. Representative cross sections developed with USGS 7.5 minute quadrangle maps <br />should be acceptable to the SEO in the. Grape Creek Canyon area between the reservoir and <br />Canon City.. Mr. Graber has indicated that the IDA will probably require more detailed cross <br />section geometry at critical locations along the Arkansas River through Canon City, to provide <br />a better estimate of incremental dam failure depths and velocities in this area. Appropriate <br />detailed cross-sections through Canon City may be available from existing flood studies available <br />through the Federal Emergency Management Administration (FEMA). Surveyed cross-section <br />data will be required if the information is not available through FEMA or state agencies. We <br /> <br />~~ID.. <br />