To determine the discharge under the maximum available head, for maximum and minimum hydraulic loss assumptions, the relationship-g- = ( Tt-) is used, where: h = maximum available head, or the difference in elevation between maximum reservoir water surface and centerline of gate, or 6101.0 - 5771.0 = 330.0 feet; Q = discharge corresponding to maximum head; hj = computed head loss; and Qj = discharge for which head losses were computed, or 1,000 second-feet. Q = 18<1Q0 = 2, 010 second-feet The computation for open channel flow with minimum losses is shown_on figure 41. The trajectory of the tunnel invert at its intersection with the spillway chute was based on the equation: x = abscissa; y = ordinate; and hv = velocity head at the start of the curve. With hv = 107.82, x2 = 431.28 y. 6. Structural Design of Auxiliary Outlet Worfes 66. General. The general loadings and allowable stress data used in the reinforced concrete design of the auxiliary outlet works follows the provisions of the ASCE "Recommended Practice and Standard Specifications for Concrete and Reinforced Concrete," 1940 edition. The designs were based on the use of concrete having a compressive strength of 3, 000 pounds per square inch at 28 days. Special loading conditions, allowable stress limitations, and other data are discussed in the sections on specific structures. To determine the loading conditions which would result in the greatest stresses and least stability of the structures, alternative analyses using various combinations of assumptions were made. 67. Intake Structure and Tunnel Upstream of Gate Chamber. The intake structure was designed for dead loads plus an external load of 40 feet of water. Normal loading conditions for a circular tunnel located in rock, as encountered in the pressure tunnel upstream of the gate chamber, would require littf" or no reinforcement. However, to protect against uncertain loading conditions, the rock in the portal area was 2.97 SHEET.. PROJECT: C. R.S. - Novajo Dam -- MAX. R. W.S. El.--DETAIL: Outlet Works -- % Tunnel ------Q=_2010 ------c.t.. Sy = K.F. (nv)? SET=--- tor ---- "n"= .008 ...DATE: 7-1-59...INITIALS:_ IL ET. FLOOR ET. E.G.L. +d+hy - LOSSES -36878 Hito 58.22 108.64 0.02 1.36554 11.06 15768.92 16007.17 6007.12 1.25206 29.09 5767.93 5978.05 5978.05 .21153 26.80 15766.84 5951.26 5951.25 .17795 22.15 5765.77 15929.11 5929.10 1.15186 18.66 15764.71 5910.45 5910.44 1.13067 15.78 3.70 22.20 90.84.127.27|13.40 1.657231 .2104 | 15763.67 5894.66 5894.66 1.10947 20.79 " 4.02 24.12 83.33 107.82 14.04 1.718 .220 .09790 | 15762.03 5873.87 5873.87 Figure 41. --Computations for open channel flow in auxiliary outlet works. assumed to be fractured, cohesionless, and the first 50 feet subjected to a uniform vertical load with corresponding base reactions from 60 feet of rock. Alleviating side loads were not considered. This severe assumption was relaxed with distance from the portal, and the reinforcement was reduced to zero about 200 feet from the intake portal. At the gate chamber the tunnel was designed for full hydrostatic internal load with no support or reaction from the surrounding rock considered. Upstream from the gate chamber the reinforcement was gradually reduced to zero, and about 300 feet of tunnel midway between the portal and gates was unreinforced as the internal and external loads were considered balanced. 68. Gate Chamber. This structure was designed for full hydrostatic head. The chamber itself was considered as a vertical cylindrical shell, fixed on the supporting base, with the hemispherical dome cover designed for exterior load only. The substructure which houses the gates, gate transition, and conduit liners was designed as a modified horseshoeshaped section assumed subjected to either external or internal pressures. The secondstage concrete was designed for full hydrostatic pressure in the construction joint between the first- and second-stage concrete with the gates in closed position. 69. Tunnel Downstream of Gate Chamber. The first 100 feet of tunnel downstream from the gate chamber was designed for an external load egual to the full reservoir head. Beyond this point, except for the exit transition, the design load was reduced to a hydrostatic equivalent of 50 feet. Drainage holes were provided to relieve pressure. The exit transition portal section was designed for an assumed vertical load of 50 feet of loose rock and a horizontal load equal to one-third of the vertical load. D. River Diversion During Construction 70. Diversion Studies for Handling Riverflows. Predicted riverflow studies for 5-, 10-, and 25-year frequencies were conducted (see subsec. 23(e)), and the basic data for the spring flood controlled the designs for river diversion during construction. In order to be able to pass a large stump or tree and to avoid an unreasonably high cofferdam, it was considered desirable to provide about a 20-foot-diameter diversion tunnel. Flood routings were made for various tunnel sizes and floods. When it became apparent that an auxiliary tunnel was required to provide continuous flow during construction, a 7-foot-diameter tunnel was adopted for this purpose and the main outlet reduced to 18 feet 9 inches in diameter. The capacity of these two tunnels approximated the capacity of the original 20-foot-diameter tunnel considered. Selection of the 18-foot 9-inch diameter tunnel was made on the basis of routing a 25-year flood, which gave a maximum reservoir surface at elevation 5831. 5 and a discharge of 14, 150 second-feet. Construction of a cofferdam adequate for this condition was considered reasonable and practical. 71. Diversion Plan. The plan for diversion of the river during construction to meet flow requirements was as follows: (1) Pass the full flow of the river in the natural or modified channel. (2) Construct a cofferdam and direct the flow through the main outlet works after completion of the following permanent construction: Diversion approach channel, stilling basin, diversion discharge channel, and outlet channel to river; (3) Install stoplogs in the intake structure and pass the required flow through a 36-inch-diameter bypass pipe during closure operations while the reservoir water surface rises to the auxiliary outlet tunnel. (4) Divert flows through the completed auxiliary outlet works while the main outlet works is being completed. |