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I I I I I I I I I I I I I I I I I I I Feasibility Report for Dam Safety Modifications to DeWeese Dam April 22, t997 9 3. DESCRIPTION AND EVALUATION OF ALTERNATIVES 3.1 GENERAL Three alternatives were developed to address the identified dam safety issues at DeWeese Darn. The first two alternatives involve physical rehabilitation of the darn structure, allowing continued, long-term use of the reservoir at its present storage capacity, The third alternative considers the impacts to the Company and shareholders ifno action is taken to resolve the dam safety issues, As discussed in Section 1,1, the dam safety deficiencies at DeWeese Darn can be summarized as: 1. Excessive weathering and deterioration of the concrete in the two crest raise sections; and 2. Inability of the l2-foot-high crest section to safely withstand all expected loading conditions in accordance with current dam design criteria, The approach taken in developing and evaluating the alternatives was to consider the top 12 feet of the darn, comprising the two crest raise sections, as a gravity darn, with the original darn acting as the foundation, 3.2 DESIGN CRITERIA Basic design criteria for concrete dams dictates that the structure must be stable and capable of withstanding the internal stresses developed by all externally-applied loads, including water, ice and seismic forces, and by the weight of the structure, with appropriate factors of safety, In general, loading conditions and stability and stress performance criteria for concrete gravity darns as developed by the U,S, Bureau ofReclarnation (USBR) [5] were used for this study, The use of USBR analysis and design principles is consistent with SEO design requirements, Specific loading conditions and performance'criteria are: %006\REPORTS\FEAS\TEXT.NEW ~ GEl Consultants, Inc,