CRETE STRUCTURE DESIGN

AL. The criteria for determining the et conduits were: (1) Discharge about t per second at reservoir elevation 3547 tion needs without dependence on ases, and (2) velocities in the conduit eed 70 feet per second at maximum Two outlets were installed in the dam. t is used to supply irrigation needs. The or evacuation outlet, is provided for uation of the reservoir. This outlet was andling the river discharge during the I to close the diversion tunnel. The he intakes are set at elevation 3400 for outlet and elevation 3300 for the et.

consists of an 84-inch-diameter steelth a cast iron bellmouth intake, a ate for emergency closure, a hollow-jet tion, and a stilling basin. The entrances are protected by a semicircular reinte trashrack structure provided with racks. The trashrack structure extends 572.7 which is about 26 feet above the active space. A bulkhead gate on the of the dam was provided to permit er outlet for subsequent examination or e steel-lined pipe and the ring-follower arrangements of the outlet works are e 73.

TION OF LOCATION. Because the Iding occupied the entire bottom width the best arrangement for the outlets in n a 60-foot-wide block immediately to e penstock blocks. The intakes to the piggyback at different elevations, but come parallel in plan after the second d at elevation 3197. The centerline en the outlets in this parallel area, 22 as dictated by the required stilling basin r the combined bends were established diameters. The outlets extend through outlet valve house located between the and the powerplant building to the right of the transformer deck area. The right-follower gates and the hollow-jet valves are located in this outlet

valve house. A hollow-jet valve stilling basin was used to dissipate hydraulic energy at the downstream end of the outlet works controls. To reduce cost and save space, a portion of the stilling basin was constructed within the powerplant building beneath the machine shop, and extended downstream beneath a portion of the powerplant service area for approximately 112 feet.

61. MODEL STUDIES. A hydraulic model1, built to a geometrical scale of 1:28, included the two hollow-jet valves, the stilling basin, the powerplant afterbay, and a section of the excavated channel downstream from the afterbay. The model studies were conducted to develop a stilling basin that would operate satisfactorily for a higher-than-normal tailwater resulting from storage in a downstream conservation pool, and for a low tailwater when there is virtually no storage in the pool. The model investigation was also concerned with flow conditions in the powerplant afterbay and in the channel downstream from the afterbay. As a result of the model studies, the preliminary stilling basin design was modified to allow for satisfactory operation at low tailwater. The model studies also indicated that channel bank protection would be required immediately downstream from the basin, and suggested that the bank should be protected with 3-foot-size rocks.

62. REINFORCEMENT AROUND THE OUTLETS. The major portion of the outlet conduits, except for critical locations, was not reinforced. This criterion was based on the proposition described previously under section 37 (f). The following design assumptions or procedures were used in determining the reinforcement for the critical locations:

(1) Temperature differential effect was assumed to vary linearly from 0° F. at the upstream face of the dam to 4° F. at the downstream face of the dam, and act through a 5-foot-thick ring of

concrete.

(2) For computing bursting pressure, a hydrostatic head equivalent to the difference between the centerline elevation of the pipe and a reservoir water surface elevation 3657 was used.

*Unpublished.