Located on the southern end of Lake Powell,
Glen Canyon Dam in Arizona is a Bureau of Reclamation
hydropower dam that channels the incredible force of rushing water
to spin turbines attached to generators,
that produce electricity without any carbon emissions.
The water is then released back into the Colorado River.
One of the traits of fast-moving water
is the phenomenon of eddies,
where water currents circle around an obstacle,
such as a rock or a pylon, then pushes back
upstream against the current of the river.
When dams release water,
the high speed and whitewater nature
of the emerging water can create eddies that circle back
and put damaging pressure on the spinning turbines inside the dam.
To prevent eddies, dam builders designed
a flat, concrete structure, called a tailrace or apron.
A tailrace is placed at the bottom of a dam
and delays the creation of possible eddies
by extending the exit path of the emerging water.
In 1965, dam operators allowed a high-flow release of water
through four of the hydropower production units
and three of the bypass tubes
in order to send a large volume of water
down the river from Lake Powell to Lake Mead.
The force of that water caused the concrete to break
in some of the areas of the tailrace.
Several of the concrete pieces ended up near the base of the dam
in areas that limited the effectiveness of
the hydropower units that sent water over those areas.
Over the years, the forces of water continued to slowly move
those broken slabs around and gradually
increased the inefficiency of the tailrace.
So, in March 2021, Reclamation dam operators at Glen Canyon Dam
decided it was time to repair some of the broken tailrace.
One of the broken concrete pieces was more of an obstacle
than the others pieces, and Reclamation engineers realized
that if they could lift and move that specific slab of concrete,
they could re-use it to fill one of the larger gaps that
were created when the original tailrace was broken in 1965.
This would remove an interfering concrete slab,
as well as create a flatter surface for the exiting water to cross,
which would improve the productivity of
both the tailrace and those hydropower units.
The challenge was that this particular slab of concrete
was estimated to weigh 45,000 pounds
-- that’s about as heavy as 23 small cars.
So how did they lift and move such a
heavy chunk of concrete, underwater?
After reducing power production and water releases
to just a few hydropower units,
Reclamation scuba divers dove down and installed metal rings
into the top surface of the broken concrete slab
that they had previously selected.
To the rings, they attached deflated balloons,
specifically designed to lift heavy objects underwater.
The divers then filled the balloons with air,
causing the buoyancy of the balloons to
overcome the weight of the slab,
lifting it off the river bottom just high enough
to clear the other rocks and concrete slabs in the area.
Once the slab was lifted,
the scuba divers were able to simply push and guide it
through the water to the identified location and guide it
into its new resting place
and deflate the balloons.
These efforts improved the flow of water out of the dam gates,
and increased the productivity of those hydropower units again.
The ingenuity of these dam operators and maintainers
allowed this work to be completed, while still meeting
the power production and water delivery requirements of the dam.
This is just one of the many ways the Bureau of Reclamation
uses critical thinking, creativity, and problem solving to maintain
and improve the facilities we use to conserve and manage
limited water resources,
while also producing clean energy
for communities in the mountains and deserts
of the southwest.