to place concrete in the gate chamber.

Provision was therefore made to install the gates in "second-stage" concrete. However, the gates were available and were installed in the first-stage construction.

21. Hydraulic Design of Outlet Works. Several schemes, trials, and computations were made to arrive at the outlet works layout finally adopted. Based on an outlet requirement of 600 cubic feet per second with reservoir water surface at elevation 9963.0, the principal head losses were computed as follows:

This loss checks closely the total 70-foot head available between reservoir elevation 9963.0 and the centerline of the outlet valve, elevation 9893.0. The ratio

was used to determine water surface elevations for various discharges. For very low heads the control is at the throat of the trashrack structure.

22. Structural Design of Outlet. The trashrack structure (fig. 8) was designed for a 40-foot hydrostatic head and checked against a 24-inch ice slab loading. Working stresses for concrete were based on a 28-day strength of 3,000 pounds per square inch. The allowable steel stress for the conduit and upstream tunnel was 12, 000 pounds per square inch; and for all other structures it was 20,000 pounds per square inch. The conduit just downstream from the trashrack was designed for an external load equal to the full reservoir head of 140 feet. The 6.5-foot-diameter pressure tunnel was designed for an internal load equal to the full head (140 feet) at the gate chamber and decreasing uniformly to 40 feet at the inlet portal, and for an external load decreasing from 140 feet at the inlet portal to zero at the gate chamber. Some elliptical hoop reinforcement was specified to utilize the steel to the best advantage. The downstream tunnel was not reinforced except for a 40-foot length adjacent to the gate chamber and a 40-foot length at the outlet portal.

The anchor block was designed for hydrostatic and dynamic forces and checked against sliding. The valve house floor was designed for an H 15-44 truck loading plus a 10 percent impact load. When the discharge valves are repaired or replaced, it is desirable and provision is made to load or unload them directly onto or from a truck in the valve house. The roof slab is designed for a live load of 100 pounds per square foot and a dead load of 125 pounds per square foot.

A

Three separate designs of a retaining wall adjacent to the valve house were made. design based on field data available in the Denver office was made. A suggestion for realinement was made by the construction engineer, who submitted additional information. Later, when the redesign was reviewed by the construction engineer, it was agreed to compromise the two previous layouts and a third design was made. Design data for the final design are as follows:

The above values were used in the Rankine formula for earth pressure, P-Cwh, to obtain the intensity of earth pressure behind the wall.

23. Outlet Works Electrical and Ventilation Systems. (a) Electrical System. The prime contractor was required to install in the outlet works valve house an electrical system for operating all power and lighting equipment at the dam. The equipment consists of a gasoline-engine generator set with distribution cabinets in the valve house and circuits leading to the points of use. Branch circuits lead to lighting system outlets in the valve house, the gate chamber, and the tunnel between these two structures, and to electrically operated equipment located in the valve house.

(b) Ventilation System. --A forced ventilation system is provided for the gate chamber and tunnel when it is required that men enter these structures for inspection or maintenance work. The ventilation system consists of a fan mounted on a wall bracket in the valve house, and 8-inch-diameter slip-joint duct leading from the fan in the valve house through the tunnel to the gate chamber, and a discharge head in the gate chamber. The pushbutton station for starting the fan is located in the valve house. The return air from the gate chamber flows through the tunnel to a louvered opening in the valve house wall, and then to the outdoors through the louvered opening. The ventilation system is designed to provide nine changes of air per hour to the gate chamber, and one change per hour for the combined tunnel and gate chamber.

The ducts were made of No. 20 U.S. S. gage copper-bearing galvanized sheets for corrosion resistance, and the other steel parts of the system were galvanized.

24. Welded Plate Steel Outlet Pipe. (a) General. --A single 56-inch-diameter welded plate steel outlet pipe is provided for releasing water from the reservoir. The general layout and the details of the pipe are shown on figure 9. The water flows through a 6.5-foot-diameter concrete conduit buried in the dam to the gate chamber where it enters the steel outlet pipe. The steel flange at the upstream end of the pipe is bolted to the cast-iron liner of the high-pressure gate. In the horseshoe-shaped tunnel downstream from the gate chamber the steel pipe is supported on small concrete piers spaced 36 feet along the tunnel axis. At the downstream end the pipe is bifurcated by means of a wye into two 48-inch branches each of which is controlled by a 48-inch butterfly valve bolted to the steel flange of the pipe. The wye is completely embedded in the concrete of the valve house structure, which also serves as a pipe anchor.

An expansion joint located approximately midway between the gate chamber and the valve house takes up temperature movements of the pipe. The support rings of the pipe slide on self-lubricating bronze plates to reduce friction during temperature movements. The pipe can be drained through the butterfly valves. A 4-inch drain at the upstream end serves to drain the gate leakage when the pipe is unwatered for inspection and maintenance, and a 4-inch drain at the downstream end of the tunnel is used to release water left in the pocket formed by the wye which cannot be drained through the butterfly valves. Two 20-inch manholes provide access to the interior of the pipe for inspection and maintenance.