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3.20 The tunnel under the left abutment of the dam would be excavated in sandstone of the Middle Haystack Mountain Formation probably by conventional drill-and-blast methods. The rock would be supported temporarily by rock bolts and protected with shotcrete as necessary. The tunnel would slope 0.833 percent and would be excavated to approximately 13 feet in diameter to achieve an 11-foot final diameter with a 1-foot-thick lining. The 11-foot inside diameter with concrete lining would be able to pass the 10-year flood of 1945 cfs during construction. The other Long-term functions of water supply, possible emergency drawdown, and possible future hydropower would be facilitated by a 66-inch-diameter pressurized steel pipeline inside the tunnel.. 3.21 There would be two valves in the outlet valve house: a 42-inch-diameter valve and an 18-inch-diameter valve. These two valves would have the combined range of capacity to handle discharges ranging from flow releases of 24 cfs to maximum operation needs of 200 cfs. 3.22 The stilling basin is designed to handle- the dispersion plume from the 42-inch-diameter valve so as to preclude damage to the surrounding terrain. The discharge channel from the stilling basin to Savery Creek would be approximately 500 feet long. Its design flow is the maximum operating demand of 200 cfs. The channel would be riprapped along its entire length. 3.23 The spillway structure would be located on the left abutment of the dam. The approach channel would be unlined and slightly curved from the reservoir to the control ogee. .The ogee would be a 90-foot-long mass concrete structure with the crest set at 6,932 feet msl for storage requirements. Excavat-ion for the overflow chute sections would be made deep enough that these concrete sections could be founded on the underlying sandstone. • 3-8