The river outlets consist of two 72-inch-diameter pipes extending through the dam, emerging just to the left of the powerplant building. The pipes then reduce to 66 inches in diameter, continuing about 200 feet downstream beneath the powerplant service area before discharging into the river downstream of the tailrace. Maximum capacity of the river outlets is 4,000 second-feet. Each outlet is protected by a 66-inch ring-follower gate at the toe of the dam, and discharges are controlled by a 66-inch hollow-jet valve at the discharge end of each pipe. A bulkhead gate will provide closure at the upstream face of the dam for inspection and maintenance.

Three 10-foot-diameter penstocks are located through the central portion of the dam, each penstock serving a 50, 000-horsepower turbine. Each intake opening is protected by an 8.27- by 15.82-foot fixed-wheel gate suspended immediately above the intake opening for rapid emergency closure, which is operated by a hydraulic hoist located at the crest of the dam. One set of stoplogs is provided to permit inspection and maintenance of the seats and guides for the gates. A 70-ton-capacity gantry crane on the crest of the dam is used for the installation and maintenance of the gates, hoists, and stoplogs.

The powerplant building is located at the toe of the dam in the original river channel and houses three generating units having a combined capacity of 108, 000 kilowatts. The powerplant building was designed as a reinforced concrete substructure and a steel frame superstructure with reinforced concrete walls. A 150-ton overhead traveling crane is provided for the installation and maintenance of the generating units. The transformers are located at the generator floor elevation between the upstream wall of the powerplant building and the downstream toe of the dam. The switchyard is located a short distance beyond the right end of the dam.

25. Design Changes During Construction. There were a minimum of design changes or additions during construction. Principal changes were occasioned by the character of the rock after exposure by excavation. The upstream dip of bedding planes in the rock, plus the predominate near-vertical jointing system, created a tendency for sliding of massive slabs of rock. This tendency, plus the joint openings in the foundation rock of the dam, which did not tighten with depth as originally anticipated, caused the following changes or additions in design:

(1) Revision of the gallery layout in the dam to include transverse adits from which consolidation grouting of the abutment rock for the dam could be performed. (2) Substantial increases in the foundation grouting program, including:

a.

An increase in the number and depths of B-holes for foundation consolidation grouting (see sec. 18).

b. An increase in the number and depths of A-holes for foundation highpressure grouting, including extension of grout curtains for right abutment beyond the end of the dam (see sec. 19).

(3) An increase in the number and depth of foundation drainage holes (see sec. 21).

(4) Construction of concrete protective walls and installation of anchor bars for the protection of shale zones and stabilization of rock ledges (see sec. 15).

(5) Substitution of about 567 feet of sidehill bridge, extending from the left end of the dam, for the originally planned benched roadway.

An addition of some magnitude was the design and subsequent construction of a visitors' center in the parking area adjacent to the right end of the dam.

B. River Diversion

26. General. The narrow canyon site and the location of the powerplant at the toe of the dam ruled out the possibility of diversion of the riverflow other than through a diversion tunnel. Economic studies indicated that the most feasible location for the tunnel

would be through the right abutment rock (fig. 16). It did not prove feasible to utilize the portion of the spillway tunnel downstream from the elbow for diversion, as has been done for many other Bureau dams. The studies and conclusions as to the respective locations of the diversion and spillway tunnels are discussed more fully in chapter II.

All diversion during construction was made the responsibility of the contractor. The diversion tunnel, including the tunnel plug and the closure structure at the tunnel intake, was designed by the Bureau. The height and type of cofferdams were determined by the contractor, subject to the approval of the Bureau. After conclusion of all necessary diversion of the river, the tunnel was permanently plugged and abandoned.

27. Hydraulics of Diversion. Various designs and economic studies were made before the final diameter of the diversion tunnel was determined. Comparisons were made between an unlined and lined tunnel and it was concluded that a reduced-diameter concretelined tunnel would prove the more economical. In addition, the concrete lining would provide the necessary protection for required tunnel supports from high-velocity flows; whereas for the unlined tunnel, special protection would have to be provided for the tunnel supports.

The required tunnel diameter was determined from design floods of 5-, 10-, and 25-year frequencies, which have capacities of 14, 000, 16, 000, and 18, 000 second-feet, respectively. The 18, 000-second-foot flood was selected for determining the size of the tunnel that would require an upstream cofferdam of reasonable height for diversion. On this basis, a 23-foot-diameter concrete-lined tunnel was selected.

Various theoretical discharges were routed through the tunnel to obtain a discharge curve. This curve was included in specifications No. DC-5045 for construction of the dam, and enabled the contractor to determine a satisfactory height for the upstream cofferdam. The contractor, with the approval of the Bureau, designed and constructed the upstream cofferdam to elevation 5690, which would furnish ample freeboard for the selected 18, 000-second-foot flood. The following hydraulic data were utilized in determining the discharge curve for the tunnel:

Bend loss--0.10 velocity head
Entrance loss--0.20 velocity head

Friction loss--0.014 for coefficient of roughness

28. Diversion Tunnel Lining, Plug, and Intake Closure Structure. The overall length of the tunnel, including the intake closure structure, is about 1,100 feet. Since the tunnel was to be used for a limited time only, the lining thickness could be reduced from that normally specified for a permanent structure. A minimum thickness of 12 inches was specified for the concrete lining, based on the criterion that the thickness should approximate one-half inch per foot of diameter of tunnel. No foundation grouting was required except in the areas of the plug and intake closure structure.

The tunnel plug was constructed at about the location where the projected axis of the dam intersects the tunnel. The tunnel was keyed by varying the diameter from 29 feet at the upstream end to the normal 23-foot diameter of the tunnel at the downstream end of the plug. The 62-foot length of plug was determined by assuming a shearing stress of approximately 20 pounds per square inch at the periphery of the plug. Foundation grouting was required, consisting of seven rings of 30-foot-deep grout holes on 10-foot centers, with six holes to each ring. Periphery grouting was also accomplished at the contact between tunnel lining and plug concrete for the top 90° segment of the tunnel roof.

The upstream 50-foot length of the diversion tunnel was designed as a stoplog closure structure (fig. 17). The structure had a transition from a double-barreled rectangular section, that would accommodate the stoplogs, to the 23-foot-diameter tunnel section. The double-barreled opening was obtained by the use of a center pier, which reduced the span of the stoplogs and also the shears and moments in the structure. To further stiffen the structure, a horizontal strut between the sidewalls was incorporated into the design. Therefore, at the intake of the closure structure, there were four rectangular water passages, each 9.75 feet wide by 10.75 feet high. The intake of the structure was designed for a hydraulic head of 150 feet, with the hydraulic loading reduced to one-half this amount at the downstream end (circular section) of the closure structure. The

Width varies

NOTES

CONCRETE REQUIREMENTS

REVISED PORTAL FROM STA 0+68ITO STA. O +66.
ADDED SEC.-H.

THIS DRAWING SUPERSEDES DWG 591-0-150 IN PART

591-D-306