downstream ends, and a 16-foot width at the downstream end. It has a length of 38 feet and a height of 19.5 feet. A 6- by 7.5-foot high-pressure emergency gate, and cast-iron transition liners which connect the gate to the upstream conduit and to the downstream outlet pipe, are embedded in the substructure.

The superstructure is a 22-foot inside-diameter circular-walled chamber, with a 22-foot-diameter, hemispherical dome roof. The thickness of the dome is 18 inches at the crown and increases to 24 inches at a point 12.5 feet above the floor of the chamber. The thickness of the walls of the structure ranges from 24 inches where the walls join the dome to 26 inches at the base of the structure.

(e) Downstream Conduit.-- The downstream conduit is an 11.5-foot inside-diameter horseshoe conduit having walls 2 feet 2 inches thick. This conduit is about 256 feet long and extends from the gate chamber to the valve house which is located at the toe of the dam. The conduit is constructed similarly to the upstream conduit with respect to length of sections and joint treatment. Six cutoff collars, 18 inches wide by 3 feet high and centered on the 28-foot-long sections nearest the gate chamber, are also provided for percolation hindrance. The conduit accommodates an 84-inch-diameter steel pipe which conveys water from the emergency gate to the regulating valves. The pipe is supported from the conduit floor on piers spaced at about 35-foot centers. A walkway cast integrally with the conduit floor is located alongside the outlet pipe.

(f) Valve House.- The valve house structure is a reinforced concrete rectangular structure about 44 feet wide, 50 feet long, and approximately 46 feet high. It is located near the downstream toe of the dam adjacent to the downstream end of the conduit and consists of a substructure encasing a bifurcated outlet pipe, and a superstructure which houses the control and handling equipment for the outlet valves.

The substructure is essentially an anchor block in which a Y-branch manifold is embedded and which forms the foundation for the superstructure. Two valve pits, each 13.5 feet wide, 13 feet long, and 14.25 feet deep, are provided at the downstream end of the structure for the regulating valves. A stairway and access gallery leading from the valve house area to the conduit, is provided in the valve house substructure.

The valve house superstructure has an 8-inch-thick roof and 12-inch-thick walls. Supports for the roof, 20-ton trolley, and service hoist are provided by 3- by 3-foot concrete columns, 3- by 3.6-foot concrete girders, and 30-inch steel girders. The steel girders are spaced at 8-foot centers.

Water from the regulating valves discharges into the stilling basin which is adjacent to the valve house.

(g) Stilling Basin. -- The stilling basin (fig. 27) has a length of 75 feet, an inside width of 30 feet, and a maximum depth of 30 feet. It is composed basically of a chute, a stilling pool, and wing walls.

The chute is provided with a baffle or deflector slab 37 feet long and 30 feet wide. This baffle is 4 feet thick and spans from wall to wall approximately parallel to and about 12 feet above the chute floor slab. The floor slab is about 4 feet thick and

slopes downward at about 40° from a point about 5 feet from the upstream edge at elevation 3035.65 to elevation 3020.0 and continues at the latter elevation to the downstream edge.

The stilling pool is composed of a two-level base slab with a vertical offset, dentated sills, two cantilever side walls, and a downstream cutoff wall. It has a length and inside width of 38 and 30 feet, respectively. The side walls extend 30 feet and 21 feet above the lower and upper floor levels, respectively. The first section of floor is 4.75 feet thick and the remainder is 3.7 feet thick. Two dentated sills, 9 by 6 by 9 feet, one located on the centerline of each regulating valve, project upstream from the vertical offset in the floor. The side walls are 12 inches thick at the top, and the back face is battered 1-1/2 inches per foot.

328-0-194

328-D-195

STILLING BASIN - SUPPORT ANGLES AND GRATING.

Wing walls extend to left or right of the downstream end of the left and right stilling basin walls, respectively. The left wing wall is 29.2 feet long and is provided with three counterforts spaced at 9.6-foot centers plus a cantilever and span of 5 feet. The wall has a thickness of 12 inches at the top and a height ranging from 21 feet at the stilling basin end to 11.5 feet at the outer end. The right wing wall is about 77 feet long and is composed of two 23.75-foot-long sections and one 25.92-foot-long section. It is 21 feet high and is provided with counterforts spaced at 11.25-foot centers. The cantilever end spans of these wing wall sections are 5.33 and 7.5 feet, respectively. A 3-footwide and 8-foot-deep cutoff wall set flush with the wall face is provided in the foundation of the left and right wing walls.

(h) Outlet Channel.-- The outlet channel extends from the downstream end of the stilling basin at station 11+67.00 to the river below the dam. This is an open-cut channel 54 feet wide at the bottom, about 250 feet long, and having 3 to 1 side slopes. A 3-foot layer of dumped riprap protects the bottom and side slopes for a distance of 18 feet. Beyond this length, native rock protects the left and right slopes for distances of about 100 and 220 feet, respectively.

63. General.

1. Hydraulic Design

The outlet works structures were designed for the following minimum discharges at the indicated reservoir water surface elevations (see also section 61):

(1) 600 second-feet at elevation 3083, and

(2) 1,000 second-feet at elevation 3095 or higher.

Discharge curves are shown on figure 28. Standard Bureau practice was used for computing head losses in trashracks, transitions, bends, Y-branches, emergency gate, and regulating valves. Velocities and friction losses in the high-pressure conduit and steel outlet pipe were computed by using a roughness coefficient, n, of 0.013 and 0.012, respectively, in Manning's formula. The trashrack structure was designed to pass 1,000 second-feet at a velocity of 2 feet per second. A tabulation of velocities in various components of the outlet works under two operating conditions is shown as appendix F.

64. Stilling Basin. The stilling basin was designed in accordance with the following requirements:

(1) To provide effective and economical energy dissipation for the discharge from the two 60-inch hollow-jet valves.

(2) To provide a discharge velocity that would cause no damage to the channel, dam, or appurtenant structures.

The discharge velocity per foot of stilling basin width with both valves open and reservoir water surface elevation 3112.3 is about 43.5 feet per second.

65. Model Studies. - Hydraulic model studies of the outlet works were conducted concurrently with specifications designs. The studies were conducted in order to check the adequacy of the design for a full range of operation. A model of the original hydraulic-jump stilling basin for the outlet works was tested and found to be hydraulically inadequate and too costly. As a result, a hydraulic-jump type basin with concrete baffle or deflection load over the major part of the chute and extending from wall to wall was recommended and adopted for construction. This adopted design resulted in a more economical structure with much better hydraulic characteristics. These model tests were conducted in conjunction with the model tests of the spillway (sec. 47).