Over time the flow of water over the dam had seriously eroded the floor of the spillway at the Canyon Ferry Dam.  The erosion ranged from just a few inches deep to 2-feet deep in the center. The Bureau of Reclamation (BR) decided that it would be more cost effective to repair the spillway floor while in operation and 50 feet underwater.  It also specified a minimum concrete repair depth of 6-inches.  All areas within the repair area that were less then 6-inches deep had to be demolished down to a minimum depth of 6-inches.  This was typically around the entire perimeter of the repair area and other isolated areas.  Rampart built an Underwater Hydrodemolition Unit designed specifically to set on the spillway floor with hydraulic leveling legs.  This unit was placed on a barge along with its electric hydraulic power pack and moved over the area to be removed.  It was then lowered to the floor of the spillway and placed into position by a diver.  Once the unit was in position, leveled and ready to cut, the diver released the safety override which signaled Rampart’s technician to begin concrete removal.  Debris from the hydrodemolition operation was vacuumed from the spillway floor using water vacuums.