seven 174 you ready art okay seven 175 instrumentation ready buddy okay let's give it back to gamble and the O&M boys and see how she operates six one this is six all I'd like you to open the left spillway gates to 20,000 cubic feet per second coming to point us out [Music] the way [Music] [Applause] [Music] flowing from the summit lands of the Rockies the Colorado River responds to annual snow falls with erratic flows during the snowmelt period of April through July it can roar through the canyons in a gigantic flood or it can flow quietly and quickly fall back after the snow is gone during each of the past 80 years or so the Colorado has been measured and averages have been obtained but the river cares not for averages and seems rather to follow its own mysterious destiny in the fall of 1982 and the early spring of 1983 snow depths in the high mountains of Colorado Wyoming and Utah were only a little above average in May however heavy snowstorms hit the high country it was cold then but the heat of summer cut like a hot night and the heavy snowmelt was on first indication of flooding occurred just west of the Colorado River Basin along Utah's Wasatch Mountains hear the streams peaked quickly and filled Utah Lake to overflowing the runoff cut through the city streets of bountiful and Farmington Utah while in Salt Lake City the water was channeled out onto some of the principal streets to form man-made rivers a fascinating diversion for office workers and tourists in the Colorado River Basin itself heavy flows came from mountains in five states from Wyoming's lofty Wind River mountains the runoff rushed through fontanel dam and onto Flaming Gorge Dam where it overflowed the lake and plunged into the spillway and bypassed tools in western Colorado heavy releases from Blue Mesa Dam flowed into mortal Point Lake which then spilled in a dramatic 354th rock crystal reservoir also poured over its spillway in another dramatic freefall and from the you enter mountains of Utah flowed several streams and rivers and all of these tributaries combined from the strawberry and the dew shade from the green and the Big Sandy from the Yampa the white and the Eagle from the tummy Qi and the Gunnison from the Dolores and the San Juan from the Colorado every stream and every river poured into Lake Powell where the combined waters rose rapidly toward the spillways at Glen Canyon Dam efforts were made to control this unanticipated rise of Lake Powell by operating the power plant at full capacity thus releasing 28,000 cubic feet per second of water but it was not enough as inflow into Lake Powell rose quickly to over 90,000 cubic feet per second in early June and the left spillway gates had to be open it was understood that these spillways would probably suffer some erosion by a physical process called cavitation cavitation occurs when high-velocity flows are thrown upward by some small obstruction this causes a partial vacuum which produces vapor cavities in the water these unstable cavities then collapse sending intense shock waves against the concrete at first small pieces then larger pieces of concrete are literally pounded out after one hole has formed a leapfrog action tends to promote the start of another on down through the tunnel in stair-step fashion it was realized too that most of the damage would probably occur at the elbow section where the spillway levels out after only four days operation inspectors found that cavitation had indeed been active at Glen Canyon a photo taken by one of the inspectors disclosed holes in the concrete lining 20 feet wide and up to 4 feet deep the spillways would have to be used but the left one would carry most of the excess flow thus preserving the right spillway for any future need to reduce spillway use wooden plywood flash boards four feet high were added to the spillway gates and the outlet tubes were open to bypass an additional 17,000 cubic feet per second of water although engineers had no way to see into operating spillways they could tell what was happening by the action of the water emerging from the lower portal flip bucket on June 19th the left spillway stopped sweeping indicating that erosion by cavitation was damaging the concrete tunnel lining the flow was raised from 12,000 to 17,000 cubic feet per second and the sweep resumed but on June 28 the sweeping again ceased when the flow was raised this time to 32,000 cubic feet per second the increased flow brought forth sandstone colored water pieces of concrete and rock were hurled from the spillway obviously the spillway was being heavily damaged the floor was immediately reduced and the water cleared by this time however the peak of the spring runoff over 120,000 cubic feet per second was flowing into Lake Powell much of this inflow would have to be sent through the spillways it was a tense situation for the engineers in charge no one could enter the left spillway yet no one knew the extent of the damage hopefully we'll be able to keep them on line yeah that's really large flows and they've been that way for a long time would have to stay that way again for a long time so you can see that be very critical in their decision that we make the only way we can get additional storage is to add flash ports on top of the gates tie them back down into the gate struts and that will add additional storage in the reservoir the best solution was to hold back Lake Powell by installing metal flash boards eight feet high on the spillway gates these would replace the smaller wooden boards and would allow reasonable operations until Lake Powell stopped rising a contractor Kai F Atkinson company began installing the boards on the fourth of July working around the clock within two days the big flash boards and the bracing were in place spillway flows could then be reduced by lowering the gates in addition the tunnels could be temporarily closed for an inspection engineers from the Denver engineering and Research Center boarded a small cart to be slowly lowered by a winch into the darkening cavern these men found cavitation holes so deep that they could not proceed further the rise of Lake Powell slowed as expected and by late August 1983 all spillway flows were shut down first item on the repair schedule was to inspect the damage in the left tunnel cavitation had initiated a series of large holes about eight to ten feet deep and 25 feet wide they found the concrete lining gone for several feet up the sides steel reinforcing bars vibrated so violently by the moving water that they had broken off from metal fatigue before them a huge underwater hole of unknown depth altogether it was to be a massive repair undertaking to cost millions of dollars and there would be a rush the rain and snow that had caused the high river flows of 1983 showed no signs of abating in fact as 1984 approached frequent heavy fall rains and early winter snows swept into the distant headwater mountains with no time to waste the contractor began an access route a 180 foot long tunnel cut into the side of the Left spillway [Music] a temporary roadway was placed across the powerplant transformer deck and a similar access tunnel was cut into the damaged right spillway with the standing water finally pumped out the spillway disclosed an amazing array of rock rubble that had been gouged from the tunnel floor including this huge boulder that had been broken loose and lifted out by tons of falling water most astonishing of all was the big hole at the elbow section found to be 32 feet deep 40 feet wide and 150 feet long within a few days concrete was flowing into the hole 2,500 cubic yards were needed to fill it broken eroded concrete was removed by drilling and blasting to reshape the tunnel to make it ready for a new three-foot thick concrete lining dangerous work but performed carefully by drilling ahead and under the old concrete [Music] and to keep the sandstone in place Rock bolts several feet long were tightened into place as the winter came on a curtain was drawn over the spillway portals to keep out the cold desert winds but in the mountains the snow continued to deepen it was beginning to appear that the Glen Canyon spillways might indeed be needed in 1984 Lake Powell had been drawn down 27 vertical feet which represented an immense amount of available storage but was it enough a continual problem at the Glen Canyon spillway repair as well as a major source of discomfort to the workers was the water that seeped into the tunnel and fell like rain or like a waterfall much of the water could be collected in pipes and directed to pumping stations [Applause] worth then proceeded on the network of reinforcing steel bars and the placement of the new concrete lining [Music] [Music] [Music] [Music] meanwhile at the engineering and research center of the Bureau of Reclamation in Denver scientists and engineers worked quickly to redesign the spillways a model of the Glen Canyon spillways was used to design notches called air slots since cavitation can never be completely eliminated a cushion of air bubbles can be introduced that will absorb the shock of the collapsing vapor cavities this will prevent damage to the concrete a notch of precise size and shape cut into a spillway turns this water white with air bubbles that foam into the rushing water the technology of air slots was unknown when Glen Canyon Dam was built in the early 1960s up to this time it was believed that the only solution for cavitation damage on Tunnel type spillways was to provide smooth surfaces but in time even the smoothest surface Ruffins with calcium deposits or small cracks in the concrete a number of Reclamation dams with tunnel spillways were spared damage from cavitation only because the spillways were rarely if ever used and then only for small amounts of water after the effectiveness of air slots was demonstrated in laboratory research they were installed in the spillway at yellowtail dam in Montana and in the spillway at Flaming Gorge dam in Utah but neither yellowtail nor Flaming Gorge had the magnitude or the particular design features of Glen Canyon Dam a series of laboratory investigations determined that the air slots at Glen Canyon had to be four feet wide four feet deep and had to be located 253 feet below the spillway gates a long way down into a steep dark tunnel where seepage water poured in eternal rains the platform hung from cables served as a space station for the drillers who pierced the old concrete lining almost 3,500 times [Music] [Music] [Music] [Music] [Music] from the rim of the canyon concrete for the air slots was then fed through a long pipe line into the spillway [Music] the forms were then removed to reveal the completed air sloth as the work proceeded on the air slot Lake Powell began its annual spring rise upward toward the top of the spillway gates with forecasts of snowmelt runoff also rising it began to look like 1984 would be another record high water year the question was if needed would at least one of the Glen Canyon spillways be ready in time to slow the rise of the lake the outlet tubes were opened on May 4th at one time the inflow into Lake Powell reached 148 thousand cubic feet per second but the lake slowed its rise and finally stopped two and a half feet on the flashboards the lake was not to spill in 1984 in spite of the fact that the runoff during 1984 was the highest ever recorded on the Colorado River higher even the 1983 in late spring the work platform was withdrawn and the completed air slot could be seen against the full dimension of the spillway the small air slot was deceiving for the engineering design and construction of the air slots were difficult achievements the completed spillway was inspected to make sure that all surface imperfections were repaired [Music] what remained was the dramatic test of one of the spillways to make sure it would operate as planned hopefully without cavitation one-seven-five instrumentation [Applause] [Music] [Music] [Applause] [Music] after each phase of the five days of testing Bureau of Reclamation officials carefully inspected the left spillway for any damage absolutely no cavitation damage could be detected the design and installation of the air slot was a complete success through the spillway had roared water at over 1500 tons per second at a velocity exceeding 100 miles per hour yet it had caused no cavitation altogether the repair of the Glen Canyon spillways and the flawless design and installation of air slots in less than a year had been a monumental accomplishment of course it had been a triumph of technology but it was even more a victory for the human spirit for the leaders who cut through the red tape [Music] for the experts who tested planned and designed for the men and women who worked long hours and who did the job the American people who owned this big Dam and Lake Powell can now be confident that when the next floodwaters rushed down the unpredictable Colorado River Glen Canyon Dam and its spillways will be ready [Music]
Documentary on the damage to the Glen Canyon Dam spillways, repair, and addition of 'air slots' to reduce future damage from cavitation.