3000

Assumed rock surface

Assumed rock
surface

-2400

-48200

+2000

1000

ELEVATION

Figure 32. --Trinity Dam spillway as built. This is the same design as figure 39 with modifications made subsequent to specifications issuance.

Figure 33. --Trinity Dam spillway crest structure--Concrete and reinforcement details.

Flow from the auxiliary outlet works is introduced into the spillway tunnel at its crown, directed at an angle of 45° to the centerline of the tunnel, about 1,000 feet upstream from the tunnel portal. The downstream portion of the structure thus accommodates flows from both the spillway and auxiliary outlet works.

53. Hydraulic Design. (a) General. --The hydraulic design of a morning-glory inlet structure and of a flip-bucket terminal structure as used at Trinity Dam is based on empirical concepts determined from previous model studies and on generalized theoretical analytical procedures. From a preliminary layout based on the theoretical and empirical assumptions, hydraulic model studies were initiated. Because of the complexity of problems involved in studying the details of prototype performance as represented by a model, and because it was impractical to represent both the inlet and the downstream tunnel and channel in a single hydraulic model to a common scale, a 1 to 30 scale model was built to study the inlet and tunnel operation, and one model on a 1 to 80 scale was built to study hydraulic flow and conditions at the flip bucket and downstream area.

(b) Design Capacity. --As discussed in section 51, an assumed maximum spillway capacity of 24,000 second-feet at approximately reservoir water surface elevation 2387 was selected for the preliminary layout to be model tested. All component parts of the structure were to be proportioned to safely pass this discharge. With the inlet structure design as finally developed from the model tests, the maximum discharge was reduced to 22,400 second-feet at reservoir elevation 2387 (fig. 36). Flood routing of the inflow design flood (fig. 30) indicated a maximum discharge of 22, 500 second-feet at reservoir elevation 2387.8, but the design was considered acceptable as reasonably conformable to the original design premise.

(c) Inlet Structure and Tunnel:--The spillway layout prepared to initiate model testing is shown in figure 37. The crest shape and coefficient of discharge were developed from data previously established from other model studies. 8/ The crest profile was based on an assumed aerated nappe with a negligible velocity of approach. The shape was based on the lower nappe profile of a jet issuing over a 53-footdiameter sharp-crested weir operating under a head of 17. 7 feet. This profile provided a 50-foot diameter at the crest of the inlet, elevation 2370. This profile was adopted for a distance of 25 feet below the crest level.

8/Wagner, W. E., "Determination of Pressure-Controlled Profiles," one of three parts of Paper No. 2802, "Morning Glory Spillway: A Symposium," Transactions of the American Society of Civil Engineers, vol. 121, 1956.