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<br />-; <br /> <br />Ms. Honey R. Moschetti, President <br /> <br />-4- <br /> <br />December 19, 1994 <br /> <br />4. Results of concrete core tests performed in 1986. <br /> <br />5. A letter report prepared by GEl in 1987 presenting 100-year flood studies and <br />simplified stability analyses for the 100-year flood overtopping condition. <br /> <br />6. Limited design and construction drawings showing features of the original dam <br />construction and subsequent raises. <br /> <br />The dam is known to have withstood significant flood events. There is evidence of overtopping <br />depths of up to two feet, without any apparent adverse effects on the dam or foundation. <br />Additionally, there are undocumented reports of overtopping by as much as five feet. <br /> <br />General Performance Criteria <br /> <br />Concrete dams must be stable and capable of safely withstanding internal stresses developed by <br />all externally-applied loads, including water, ice and seismic forces, and by the weight of the <br />structure. In general, stability and stress performance criteria (e.g. sliding stability factors of <br />safety and allowable stresses) used in our evaluation of DeWeese Dam follow practices <br />recommended by the U.S. Bureau of Reclamation (USBR). <br /> <br />Hydrologic performance criteria for Colorado dams are established by the SEO. These criteria <br />dictate the flood event which a dam must be capable of withstanding with acceptable factors of <br />safety, according to the dam's hazard classification. The SEO has classified DeWeese Dam as <br />a "moderate" hazard dam. According to current SEO regulations, moderate hazard dams are <br />required to be capable of safely withstanding a runoff (flood) event equivalent to 50 percent of <br />the probable maximum flood (PMF). <br /> <br />Previous hydrologic studies performed for DeWeese Dam have indicated that the.2Q.lleI:c.en!J~Mt_, <br />e~?~~~ r~s_lllt in.~.g~* ~gute~.9U!fl5?~_!!0n.:!~e r~~~~voi~ ?! ~~ou~~J~,009~fs. This .<>~_t~~~ <br />would overtop the dam by as much as 23.8 feet. <br /> <br />STABILITY EV ALVA TION <br /> <br />Description of Analyses and Assumptions <br /> <br />Simplified stability and stress analyses were performed for the upper 12-foot section of the dam, <br />representing the two concrete raises constructed on the original dam. These two raises are <br />collectively referred to in the remainder of this report as the "raise section." The analyzed raise <br />section. is shown on Figure 1. The analyses were limited to this section of the dam for the <br />following reasons: <br /> <br /><J.4J II\DDREPORT L TR <br />