established for the protection of the partially completed work on the basis of approximate flood-routing studies. From existing streamflow records covering a period of 45 years, the maximum 1-, 2-, 3-, 4-, 6-, 9-, and 12-month flows of record were determined for operating periods beginning at the start of each of the 12 months of the year. These maximum flows were routed through the reservoir assuming the water surface to be at elevation 2006 at the beginning of the inflow period and the auxiliary outlet works discharging at capacity. These studies indicated a maximum water surface elevation of 2305 for the 9-month period.

In 1960, when the contractor requested permission to close the first-stage diversion openings in the outlet works intake structure, the problem was again restudied. At that time the dam had been completed to elevation 2200 and the spillway to elevation 2370. A seasonal inflow design flood and a 100-year frequency flood for a 12-month period were prepared by the Denver office. These floods and the runoff for the 1957-1958 water year were each routed through the reservoir assuming the auxiliary outlet works to be discharging at maximum capacity. The results of these studies showed that the requirements for closure established by the specifications were reasonable, and the contractor's request was denied.

(d) Third-Stage Diversion.--An auxiliary outlet works was selected as the most desirable and economical scheme to maintain minimum releases through the damsite during completion of the outlet works and powerplant construction. Several alternate locations and arrangements were studied before selection of the final plan shown on figure 53. A discussion of the design of the auxiliary outlet works is contained in sections 58 through 60.

C. Penstock System

62. Penstock System Description. (a) General. --The penstock system consists of a 16-foot-outsidediameter welded plate steel penstock header which begins at the outlet works gate shaft structure and extends approximately 1, 400 feet downstream, as shown on figures 47 and 58. The tee and bend sections, secured by embedment in concrete anchors, provide for the penstock connections at stations 43+64.85 and 44+24.24. The steel penstock header is joined to the outlet pipe through a reducing section which is embedded in a concrete anchor. The outlet pipe extends approximately 180 feet downstream where it enters into a wye branch and separates into two 7-foot 3-inch outside-diameter connections which terminate at the 84-inch ring-follower gates and hollow-jet valves within the outlet control house (see secs. 85 through 88). Bend and wye branch sections are secured by embedment in concrete anchors. Ring supports are located on each end of the sleeve-type coupled pipe sections which make up the steel penstock header and outlet pipe. Pipe movements within the sleeve-type coupled field joints, due to temperature changes, are allowed by the sliding ring support base at the downstream end of each pipe section. The ring supports rest on piers provided at maximum 40-foot spacings within the tunnel and along the exposed portion of the steel penstock header and outlet pipe.

The two welded plate steel penstocks, with sleeve-type coupled field joints, are buried under approximately 20 feet of fill and extend downstream from the tee branch and bend section connections, 190 feet for penstock 1 and 145 feet for penstock 2, to two flanged butterfly valves in the powerplant, as shown on figure 59. Two 10-foot 9-inch outside-diameter flanged pipe spools, 13 feet 8 inches long, provide the connection between the downstream end of the butterfly valves (sec. 158) and the turbine spiral case.

A 10- by 20-foot fixed-wheel gate (sec. 83) is located on the upstream end of the steel penstock header and serves as an emergency shutoff and as a service gate to permit unwatering of the penstock system for inspection and maintenance.

A 158-inch butterfly valve and a sleeve-type coupled expander piece are installed on the downstream end of each penstock. The sleeve-type coupling is installed to provide for temperature movements and to permit the removal of the butterfly valve, if necessary. The butterfly valve is fully open during operation and serves as a shutoff valve when the turbine is down for repairs.

The flow through the outlet pipe and wye branch is regulated by two 84-inch hollow-jet valves in the outlet control house. Each hollow-jet valve has an 84-inch ring-follower guard gate which serves as a shutoff when maintenance work is necessary on the hollow-jet valves.

A 12-inch, cast-steel, chain-operated wedge gate guard valve and a 12-inch, cast-steel, motoroperated wedge gate regulating valve are provided in the filling line which connects the 28-foot-diameter tunnel with the steel penstock header at the gate shaft structure. The guard valve is normally open and the regulating valve is normally closed.

A 24-inch-diameter air vent in the gate shaft structure releases or admits air during filling and unwatering operations. The 8-inch nozzles located at the downstream end of each penstock are for water, drain, and test connections. Two 12-inch nozzle connections are provided at the upstream and downstream ends of the steel penstock header for drainage. A 20-inch manhole and an 8-inch cooling water takeoff nozzle are provided on each of the pipe spool connecting sections in the powerplant. Access to the steel penstock header and outlet pipe is provided through 20-inch manholes located at approximately 200-foot intervals along the pipe.

(b) Filling Penstocks. --The penstock system will be filled from the reservoir through the 28-footdiameter tunnel. The fixed-wheel gate at the gate shaft structure will be closed. Before beginning the filling operation, the turbine wicket gates in the powerplant and the 84-inch hollow-jet valves in the outlet works control house are closed. The penstock system is filled by opening the 12-inch motor-operated gate valve in the filling line. When the penstock system is full and under reservoir head, the fixed-wheel gate is opened, and the motor-operated gate valve in the filling line closed.

(c) Draining Penstocks. --In preparing to drain the penstock system, the unit will be taken off the line and the turbine wicket gates closed. The 84-inch hollow-jet valves in the outlet works and the 158-inch butterfly valve in the powerplant are closed prior to closing the 10- by 20-foot fixed-wheel gate in the gate shaft structure. After the fixed-wheel gate has been closed, the penstock header and outlet pipe are drained to elevation 1933.72 by partially opening one of the hollow-jet valves in the outlet works. Then the other hollow-jet valve is opened to drain the water from the connecting outlet pipe branch. The remaining water in the penstock header branch is drained to the drainage sump by opening the 8-inch gate valve in the penstock drainline.

1. Penstock Header and Outlet Pipes

63. General Description. The 16-foot-outside-diameter steel penstock header (fig. 58) was designed to convey water from the outlet works gate shaft structure to the outlet works control house and to two generating units in the powerplant. The penstock header is approximately 1, 400 feet long, with a centerline elevation of 1946.30 at the upstream end that is embedded in the gate structure concrete and a centerline elevation of 1941.61 at the upper penstock branch. The two penstocks (fig. 59), which branch from the penstock header at penstock branches 1 and 2, are 11 feet 3 inches in outside diameter. The outlet pipe (fig. 60), which continues in line with the penstock header downstream from penstock branch 2, is 11 feet 3 inches outside diameter. The 11-foot 3-inch outside-diameter outlet pipe enters into a wye branch

NOTE

PENSTOCK HEADER AND OUTLET PIPE