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<br />001G57 <br /> <br />diameter manholes are located along the steel pipe for inspection purposes, and a 6-inch-diameter <br />pipeline and an 18-inch-diameter air vent pipe are provided at the upstream end for filling and <br />draining. The downstream portal section includes a 30-inch-diameter wye branch to the right side <br />at an angle of74.5 degrees (from centerline), a llO-inch-diameter wye branch to the left side at an <br />angle of60 degrees, and a 30-degree bifurcation from the 110-inch-diameter main pipe to two 72- <br />inch-diameter pipes. The two 72-inch-diameter pipes bend downward 24 degrees, and each <br />includes a 72-inch ring-follower guard gate followed by a 72-inch hollow-jet valve. Outlet <br />releases through the two 72-inch hollow-jet valves enter a stilling basin and downstream outlet <br />chaMel. The outlet chaMel rises on a 6: 1 slope from the stilling basin floor at elevation 5678.0 to <br />elevation 5710.0, where it merges with the spillway into a 600-foot-wide, riprap-lined outlet <br />channel to the San Juan River. Smaller outlet works releases through the 30-inch-diameter wye <br />branch travel about 140 feet to a control house containing a 30-inch ring-follower guard gate and <br />a 30-inch hollow-jet valve, located to the left of the spillway, and enter the spillway stilling basin <br />[2]. Releases through the 110-inch-diameter wye branch serve a power plant operated by the City <br />of Farmington, described in part D below. <br /> <br />Soon after the main outlet works was first placed into operation, large quantities of loose rock, <br />debris, reinforcing bars, and badly eroded concrete were discovered in the stilling basin (see <br />Prototype Operating History in Section ITI). It was apparent that loose materials had been carried <br />by the swirling currents into the basin from the downstream channel, recirculating in the high <br />velocity flow and eroding the concrete surfaces. Temporary concrete repairs were completed in <br />May 1965, and permanent modifications were developed by hydraulic model studies. Final <br />modification of the stilling basin eliminated the center wall and converging wedges of the original <br />design, added a stainless steel plate over the new, flatter upstream inclined floor, and included a <br />concrete slab over the original downstream riprap for a distance of 13 7 feet beyond the original <br />basin end sill. The modification design details for the stilling basin are shown on drawing Nos. <br />711-0-461 and 711-0-462. Laboratory testing of the modified stilling basin indicated flows <br />above 3,200 ft3/s would produce "nearly intolerable roughness" in the basin; consequently, the <br />maximum discharge in the prototype modified basin has been restricted to 3,200 ft3/s through the <br />two 72-inch hollow-jet valves since November 1965 [2]. <br /> <br />Discharge curves for the main outlet works are shown on Drawing No. 711-D-447 (revised 1967, <br />il1cluded as Appendix A). Although these curves reflect the 3,200 ft3/s flow restriction for the <br />two hollow-jet valves, a maximum discharge capacity of approximately 4,070 ft3/s is indicated <br />(by a dashed line) for a maximum reservoir water surface at elevation 6101.6, assuming the 30- <br />inch hollow-jet valve is closed. Hydraulic loss computations for the main outlet works are <br />summarized in the Technical Record of Design and Construction (see Appendix B), and result in <br />the following discharge equation for maximum losses and both 72-inch valves fully open, <br /> <br />Q = 215.8 (RWS - 5722) O,S <br /> <br />with Q equal to the discharge in fills, and RWS equal to the reservoir water surface elevation in <br />feet. Reservoir head is measured from the effective elevation of the outlet, considered as one <br /> <br />2 <br />