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The Company's engineer, W. W. Wheeler and Associates, provided technical engineering <br />in cooperation with Riverside personnel and Kumar and Associates, geotechnical <br />engineers, in the evaluation of project issues and altematives. The critical design issues <br />include: <br />1. Safely route the inflow design flood through the reservoir; <br />2. Minimize the potential for differential settlement of the spillway foundation soils with <br />respect to the structure and the dam; <br />3. Provide a watertight connection between the spillway structure and the upstream <br />concrete facing on the dam; <br />4. Provide flexibility at jointing between the new structures and existing concrete <br />facing; <br />5. Prevent floatation of spillway structures; <br />6. Prevent damaging erosion and scour around the terminal structure and <br />downstream in the foundation sand materials; and <br />7. Control seepage to prevent destabilization of the spillway control section, chute, <br />and terminal structures, and downstream outfall channel. <br />8. Return spillway discharges to the natural drainage below the dam. <br />HYDROLOGIC AND HYDRAULIC DESIGN CONSIDERATIONS <br />A flood routing of the SEO-approved Inflow Design Flood through Riverside Reservoir <br />showed that required spillinray must pass a minimum of approximately 2,500 cfs in order <br />to safely route the flood without overtopping the dam. The dam provides approximately <br />7.0 feet of freeboard and 28,000 acre-feet above the proposed spillway level for flood <br />storage and routing. The spillway alternatives provided hereafter are sized to provide <br />that routing capacity. <br />ALTERNATIVES EVALUATED <br />Four construction alternatives were evaluated for the emergency spillway at Riverside <br />Reservoir, including the following: <br />ALT-1. Do not build the project. <br />ALT-2. Construct a spillway near the left dam abutment near Station 57+00 E, with <br />discharge channel constructed back to the natural drainage. <br />ALT-3. Construct a spillway through the embankment near Station 9+00 E, with <br />discharge channel constructed back to the natural drainage. <br />ALT-4. Construct a spillway through the embankment near Station 2+00 E, utilizing a <br />modified outlet works discharge channel for conveyance of the spillway <br />releases back to the natural drainage. <br />9 <br />