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III I , III 111I I -22- III III III III III III III I III III I III III III III III 8,500 cfs. As indicated in the table above, the corresponding spillway width requirements are 120 feet for both schemes in order to provide the required discharge capacity. A crest raise of 3 to 5 feet and a discharge elevation range of 3 feet were estimated for schemes 2 and 4. The design discharge is slightly lower than for scheme 1 and includes consideration of attenuation of inflows due to increased reservoir storage created by the crest raise and routing effects resulting from combined spillway and overflow discharge. An optimization study should be completed as part of the final design work to select the least expensive combination of overflow elevation, width, and height of crest raise. The minimum overflow elevation should be selected to provide routing of at least a 100-year storm without discharge through the overtopping section. The discharge elevation for scheme 1 is 9725, which is 5 feet below the existing spillway crest discharge elevation. Hence, adoption of scheme 1 would result in a loss of up to 5 feet of reservoir storage. Losses less than 5 feet may be possible by the use of f1ashboards, provided final design eleva- tions indicate the required total discharge capacity. On the other hand, the discharge elevation for scheme 3 is 9730, which is the same as the existing spillway discharge elevation. Hence, adoption of scheme 3 would not result in the loss of any existing reservoir storage capacity. Likewise, the discharge elevations for schemes 2 and 4 are above the level of the existing spillway and no loss of existing reservoir storage would occur. Our hydraulic routing analyses indicated that an early warning system could provide from 1 to 1.5 hours of response time for evacuation of downstream residents. As previously mentioned, the minimum response time recommended by the USBR is 1.5 hours. Therefore, an early warning system at Sheriff Reservoir would provide marginal response time. The estimated cost of an early warning system by Synergetics International in Boulder, Colorado ranged from $30,000 to $50,000. In addition, our conceptual designs for sche- mes 1 and 3 indicated similar excavation and concrete construction require- ments. Although the design discharge is lower for scheme 3, the total volume of concrete required for the ogee overflow section, stilling basin, and retaining walls are similar to scheme 1. Similarly, because the spillway widths are equal and the stilling basin elevations were maintained at elevations con- sistent with the existing downstream spillway channel, excavation requirements in the upper portion of the spillway are similar. With respect to scheme 1, some reduction in spillway excavation requirement was determined for the lower portion of the channel for scheme 3, due to reduced spillway discharge capa- city. However, when the cost of the early warning system is added to scheme 3, our preliminary estimates indicate the total construction costs to be simi- lar (i.e., within $30,000 of one another). Therefore, because 1) response time of an early warning system would be marginal, 2) there are significant operational and long-term maintenance considerations for an early warning system in rugged terrain such as the Flat Tops, and 3) the costs are similar for schemes 1 and 3, we believe that scheme 1 is clearly preferable to scheme 3. Scheme 1 provides the full level of flood routing protection preferred by the SEO and requires minimal operation and maintenance. Therefore, scheme 1