(d) Definite Plan Report Design.-- Continuing studies of the Palisades project development were conducted during the period 1947 to 1951, leading to the adoption of the definite plan report scheme shown on figure 48. The scheme entailed essentially the same arrangement of structures considered previously, except that certain basic criteria and design details were modified. These modifications from the former scheme were as follows:

(1) The minimum reservoir power head level was increased to elevation 5497, establishing an inactive reservoir storage capacity at 200,000 acre-feet, and providing a total of 1, 200,000 acre-feet of active storage.

(2) To provide for more flexibility in the operation of the reservoir for flood control, the outflow capacity through the outlets at minimum power head was established at 30,000 second-feet.

(3) The installed capacity of the powerplant was increased from 30,000 to 114, 000 kilowatts.

(4) Since the spillway was to function as an auxiliary structure, to operate only after the capacity of the outlet works was exceeded, the spillway tunnel was reduced in size to that which would flow just snort of full at maximum capacity. For the selected spillway capacity of approximately 47,000 second-feet this reduced the tunnel size from a 34-foot diameter to a 28-foot diameter.

(5) For the outlet works controls, rectangular regulating gates were indicated in lieu of ring seal gates shown in the former design.

(6) For both the outlet and power tunnels, encased steel-lined tunnels were indicated in lieu of the separately housed steel pipe.

A brief description of the spillway and outlets indicated in this design follows:

The tunnel spillway, located in andesite formation in the left abutment to the left of the outlet tunnel, was designed for a maximum discharge of 47,000 second-feet at normal reservoir level, elevation 5620. Flow was to be controlled by two 20- by 50-foot radial gates. The spillway tunnel was approximately 1,900 feet long, varying in cross section from a 42-foot horseshoe-shaped entrance to a 28-foot-diameter circular-section along an inclined transition and along the near horizontal leg of the tunnel. The spillway terminated with an open concrete-lined channel 28 feet wide and 354 feet long. An unlined channel beyond the lined section was provided to return flows to the river.

The outlet works and power penstock tunnels, which served initially for diversion during construction, were located through the andesite formation at the left abutment, the outlet tunnel being placed about 200 feet to the right of the spillway tunnel. The centerlines of the outlet and power penstock tunnels were placed approximately 100 feet apart. Both tunnels were 26 feet in diameter, lined with concrete upstream from the dam axis and with concrete-encased steel liners from a point near the axis of the dam to their downstream end. A trashracked entrance with a 19. 25- by 46-foot fixed-wheel closure gate was provided at each tunnel, and manifolds at the lower ends of the tunnels branched to the regulating gates and valves and to the powerplant turbines. Flows from the outlet works tunnel were to be regulated by four 7.5 by 9-foot rectangular regulating gates and two 96-inch hollow-jet valves. The power tunnel terminated with a six-branch manifold, four branches serving four powerplant turbines and two branches emptying into the outlet works stilling basin, where flows were to be regulated by two 7.5- by 9-foot rectangular regulating gates. A 150-foot-wide stilling basin with 55-foot-high sidewalls was provided to dissipate energy of flows from both the outlet works control gates and valves and from the penstock tunnel bypass gates.

(e) Specifications Design.--Final designs for the Palisades development, culmunat ing in the preparation of specification drawings, were completed in 1951. The specifications design general plan, figure 6, shows the arrangement of features as finally adopted for construction. With minor modifications the design followed that shown on the definite plan drawing, figure 48.

B. Spillway Design

27. Description. The Palisades Dam spillway consists of a gate-controlled tunnel excavated through the andesite formation forming the left abutment of the dam. Flows are controlled by two radial gates installed on the crest of a concrete control structure. Flow is then directed through a parallel-sided open section to an inclined transition shaft which connects with a near horizontal tunnel 28 feet in diameter and approximately 1,675 feet long. The tunnel empties into a 350-foot-long concrete-lined open-cut outlet channel. The bottom width of the channel is 28 feet and the sides are sloped 1/2 to 1. The lined channel is terminated with a 3-foot-high trajectory lip, to direct flows upward and away from the end of the structure. General arrangement of the spillway is shown on figures 6 and 53, and details of the design are shown on figure 49.

28.

Design Capacity. - The Palisades Dam spillway was designed for a discharge of 47,000 second-feet with the reservoir water surface at normal level, elevation 5620, and 48, 400 second-feet with the reservoir 1 foot above this normal water surface level. Spillway flows are regulated by two 20-foot-wide by 50-foot-high radial gates, whose tops are placed at the normal reservoir level. The spillway discharge curves, determined by model test, are shown on figure 50. For free flow over the crest, occurring with the gates opened above the reservoir water level, the discharge coefficient, C, in the Francis formula Q-CLH3/2, approximates 3.3 for nearly all heads on

the crest.

29. Crest Design. The 50-foot-high spillway gates are installed in the control structure with their tops placed at normal reservoir water surface elevation 5620. The sills of the gates rest on the crest of the overflow section, thus providing a 50-foot head on the crest when the reservoir is at the normal storage level. The 30-foot-radius shape of the overflow section upstream from the gate sill approximates the undernappe profile of an overflow sheet flowing at a 50-foot head over a 10-foot-high sharp-crested weir placed on a 3 to 1 inclined approach slope. The shape downstream from the gate sill conforms to the path of a jet issuing from a thin orifice under a head slightly greater than that at the bottom of the gates. The equation of the overflow profile downstream from the gate sill, X2 = 224Y, is based on the boundary profile a jet will take when flowing through a vertical orifice under a head of 56 feet.

Flow is directed from the spillway inlet channel to the spillway control gates by side walls elliptical in plan, and a 6-foot-wide pier with a circular segmented pier nose separates the flow to the two gates.

30. Hydraulic Design of Tunnel. - Downstream from the crest, the spillway channel extends in open cut for 50 feet and then continues in tunnel section. The open channel and tunnel invert profile are a continuation of the crest shape profile to the point where the tunnel is inclined at an angle of 50° with the horizontal. The 50° inclined shaft connects with the approximately 2 percent sloped downstream tunnel leg by a 138-foot invert-radius curve. The tunnel varies in size throughout its inclined length, from approximately 40 feet high by 46 feet wide at the upstream portal, to 28 feet in diameter at the P. T. of the vertical curve. Downstream from the vertical curve, the tunnel size is constant at a 28-foot diameter.

For a maximum discharge of 48, 400 second-feet through the spillway shaft and tunnel, hydraulic flow computations, based on a roughness factor, n, of 0.014, indicate that the tunnel will flow about three-fourths full at the downstream end of the vertical curve and about 90 percent full at the downstream portal. Flow velocities will exceed 100 feet per second at the vertical curve and approximately 90 feet per second at the lower portal. Flow characteristics were also checked using an assumed value of n of 0.018, on the basis that air entrainment and swell might consume some of the excess area of the tunnel cross section. Computations indicated that the tunnel would completely fill at the downstream end under these assumptions.

31. Hydraulic Model Studies. - Hydraulic model tests of the spillway were made to supplement the hydraulic computations, and to verify the hydraulic design. During the course of the model testing, consideration was given to reducing the diameter of the downstream leg of the tunnel from 28 feet to 26 feet. It was reasoned that economic advantages could be realized if the spillway tunnel were made the same size as the outlet