TYPICAL SECTIONS OF CONTRACTORS SUPPORTS

DETAIL Z

Grout with
U3 finish

Figure 63.--Concrete supports for penstock and bypass pipes.

Figure 65.--Outlet works control house-- Plan and sections.

about half the length of the horizontal channel, to divide the upper basin into four separate sections. The tops of these dividing walls are placed at the approximate level of the control gate sills. The walls are placed so as to separately confine the flows from (1) the two left regulating gates, (2) the two hollow-jet valves, and (3) the two right regulating gates, all of which take off from the outlet tunnel manifold; and (4) the flows from the two regulating gates at the right side of the stilling basin which take off from the power penstock manifold. These dividing walls thus provide satisfactory stilling action in the basin for separate or unsymmetrical releases from the gates or valves.

1. Hydraulic Design of Outlet Works

36. Discharge Capacities. As discussed in section 33, the required releases through the outlet gates and through the powerplant turbines at minimum power head reservoir level was established at 30,000 second-feet. Under normal operating procedures, it was considered that the turbines might be operated at full gate to release about 7,000 second-feet, requiring a 23,000 second-foot release capacity from the outlets served by the outlet tunnel.

The 7.5- by 9-foot regulating gates of the type installed are intended to operate at heads up to 240 feet. Their design is an adaptation of the high-pressure gate used by the Bureau for lower head installations with certain modifications in the slot and leaf details incorporated to minimize cavitation effects. Since no previous prototype experience with this modified type of gate was available, it was not known whether unsatisfactory performance might be encountered at partial gate openings. It was therefore contemplated that releases might be necessary with the gate wide open only. On this premise, for smaller releases or for close regulation, two 96-inch hollow-jet valves were installed in lieu of one additional regulating gate, thereby offering an arrangement which will permit a greater flexibility in release sequences. The regulating devices served by the outlet tunnel accordingly consist of four 7.5- by 9-foot regulating gates and two 96-inch hollow-jet valves.

To provide a total release of 30,000 second-feet at minimum power head reservoir level, 7,000 second-feet must be passed through the power penstock tunnel. To obtain this release in the event that the powerplant is not operative, bypass lines and regulating gates discharging into the outlet works stilling basin are provided. Although somewhat smaller gates would release the required flows, it was considered that a gate differing in size from those used for the outlet tunnel would effect little economy, and identical gates were thus provided. These gates are capable of discharging about 10,000 second-feet at the minimum operating head.

Discharge curves for the outlet controls for full gate and valve openings are shown on figure 53.

Hydraulic Losses.

37. The discharge capacities of the outlet works control gates and valves depend on the net heads which are available immediately upstream from their entrances and on the discharge coefficient characteristics of the control device. The available head is the total head measured between the reservoir water surface and the center of the gate, reduced by such head losses which are incurred by the flow in traversing the waterway between the reservoir and the gate or valve.

For the 96-inch hollow-jet valve, the discharge coefficient C in the formula Q = CA √2gH has been determined by model tests to be approximately 0.70, where A is the area measured at the valve entrance, and H is the available head measured immediately upstream from the valve.

Coefficients have also been determined for partial valve openings. A dischargehead relationship for the 96-inch hollow-jet valve is shown on figure 67.