Transcript for Challenge at Glen Canyon, segment 05 of 11
The best solution was to hold back Lake Powell by installing metal flashboards 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, Guy F. Atkinson Company, began installing the boards on the fourth of July, working around the clock.
Within two days, the big flashboards 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, nineteen eighty-three, 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 twenty-five 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. All together, it was to be a massive repair undertaking to cost millions of dollars.