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<br />OOlGb9 <br /> <br />converging wedges. Gravel placed in the model baSin circulated violently in the <br />upstream portion of the basin. <br /> <br />The outlet works continued to operate at gate openings between 8 and 35 percent until <br />August 16. On August 21-24, engineersR B. Dexter and C. E. Brockway, from the <br />Hydraulics Branch, conducted tests to calibrate the holloW-jet valves. During these tests <br />golf-ball-size gravel was observed circulating in the turbulence and was at times thrown <br />above the water surface. Also, some abrasion damage was noted on the walls near the <br />waterline. The appearance of small gravel near the surface indicated the possible <br />presence of larger material on the floor of the basin. <br /> <br />The valve openings were limited to less than 10 percent into December of 1964 and the <br />reservoir droppedfrom elevation 5953 to elevation 5944 (233 to 224 feet). The valve <br />openings were increased through the latter part of December and the early part of <br />January to a maximum of about 35 percent on January 14, 1965. Symmetrical operation <br />at 35 percent valve openings continued to February 1, 1965, when the outlet works was <br />shut down. The reservoir dropped from elevation 5940 (220 feet) to elevation 5915 (195 <br />feet) during operation at 35 percent valve openings. The outlet works was operated for a <br />few hours at 21 percent valve opening on April 16 and for less than an hour on April 22 <br />and 23. On April 25 the basin was inspected by divers and soundings for the first time. <br /> <br />Severe erosion up to 5 feet deep was disclosed in the floor and through two layers of <br />reinforcement steel in the walls. Reinforcing bars were exposed, broken, and bent. A <br />cofferdam was built downstream from the basin, the basin was unwatered, and a , <br />complete inspection was made on May 3, 1965. The damage was described in the Travel <br />Report of the Head, Spillways and Outlet Works Section: <br /> <br />"The damage was even more extensive than reported by the divers with erosion exposing <br />reinforcement over half the height of the center wall. Erosion had extended through the <br />top layer of reinforcement at the 30 0 slopes just downstream of the hollow-jet valves and <br />loose cobbles were trapped behind the reinforcement at the upper end of these slopes. <br />These cobbles were deposited by the turbulent flows in the basin and indicate that gravel <br />and cobbles in the basin caused the extensive erosion damage. <br /> <br />The most severe damage occurred in the left side of the basin at the upstream end of the <br />floor and center wall. Two layers of No. 11 bars at 6-inch spacing in the wall were <br />broken and bent downstream along with No. 9 and No. 8 bars at 6-inch spacing in the top <br />of the floor slab. The horizontal floor bars at the base of the wall had loosened <br />sufficiently to aI/ow flow of water from one side of the wall to the other. On the right <br />side of the center wall the No. 11 bars were exposed and loosened but not removed It <br />appeared that many of the bars could be salvaged by bending back into position. Some <br />new bars need to be spliced and welded to the existing bars. About 70 cubic yards of new <br />concrete will he needed to replace the eroded concrete in the floor and waI/s upstream <br /> <br />12 <br />