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II I I I I I I I I I I I I I I I I I II -27- soil-cement as overtopping protection and the other project used roller com- pacted concrete (Ree). GEl has recently completed final designs for Ree over- topping protection for three U.S. Department of the Interior Dams. These concepts were reviewed and approved by several federal agencies, including the U.S. Bureau of Reclamation (USBR), the U.S. Fish and Wildlife Service (USFWS), and the National Park Service (NPS). The concept for providing soil-cement overtopping protection on Sheriff Dam, illustrated on Figures 9 and 10, is similar to the concepts that have been developed and approved on these other projects. Ree is generally the preferred material for use in overtopping pro- tection of earth dams, because of the lower cement contents that can be used with the controlled aggregate gradation used for Ree. However, soil-cement is proposed for this project because of the lack of a cost-effective local source of controlled-gradation aggregate for use in ReC construction. A properly designed soil-cement mixture should provide adequate durability for the pro- posed overtopping protection. The overtopping protection will be constructed over the central portion of the dam, as shown on Figure 9. A typical cross section of the overtopping protection is shown on Figure 10. The soil-cement is placed over a portion of the crest to prevent detrimental crest erosion and water pressure developing under the materials placed on the downstream face of the dam. The apron is constructed to provide erosion protection at the toe of the dam and prevent undermining of the facing material. The required length of the apron is esti- mated to be 50 feet in order to provide erosion protection over the toe area where energy dissipation will occur. Flow-training berms would be constructed along the sides of the overflow section and along the downstream edge of the sloping apron to contain the overflow. An underdrain system will be required to collect and discharge seepage beneath the soil-cement, and to minimize uplift pressures during overflow. Other provisions that may be indicated in final design evaluations would include additional riprap protection on the downstream edge of the overflow apron, and modification to the existing outlet works discharge. A typical detail illustrating the method of constructing the dam facing protection and the flow-train berm is shown on Figure 10. In addition to providing the overflow section, raising of the dam crest will be required. A typical crest-raising cross section is illustrated on Figure 10. Our feasibility level evaluations indicate that a crest raising of 3 to 6 feet will be required. In order to maintain a crest width in compliance with the rules and regulations of the SEO, precast concrete retaining walls would be placed on both the upstream and downstream edges of the existing dam crest and the area between the near-vertical retaining walls would be backfilled with compacted random backfill. We have assumed that a fence or safety chain will not be required along the top of the retaining walls due to the limited-access nature of the area and the need to preserve the natural appearance of the environment. Some minor modifications to the existing spillway will be required to accommodate the raising of the dam crest. These modifications may include extension and raising of the existing concrete retaining walls, construction of soil-cement training berms, or other methods as appropriate to provide increased hydraulic capacity of the existing spillway consistent with the new embankment crest elevation. Placing of riprap in the channel downstream of