The Ballard Locks have operated on essentially the same technology since they first opened 100 years ago: Gravity.
The movement of water up and down in the locks relies on enormous valves that open, allowing each chamber to flood with water from upstream, or drain downstream.
To experience this movement – and learn firsthand how the locks function – KNKX took a trip through the locks aboard the M/V Puget, a U.S. Army Corps of Engineers boat that clears debris from waterways throughout Puget Sound.
The Puget was built in 1944, to pick up seaplanes during World War II. It’s been in service in Puget Sound since the mid-1980s.
Its mission now: Pick up debris from navigable waterways – things that might get in the way of boaters, or knock against infrastructure and cause damage.
“Trees, docks, boats,” says Skip Green, who captains the vessel. “We bring it all – most of them – all back here, and we pile them up on these barges we have out there. About 90 percent of it gets recycled.”
The Puget is a sizable vessel, though far from the largest in view in Salmon Bay. It’s 104 feet long, 35 feet wide, with twin engines and a shallow draft – only a few feet – allowing it to get into some extremely shallow waters.
To get from Salmon Bay into Puget Sound, we motor our way into the large lock.
Bells sound and an enormous gate closes behind us. The gates swing upstream, and they are mitered – two enormous walls that meet at an angle. This prevents them from being pushed open by the higher water.
Underneath the M/V Puget, enormous valves are opening and water rushes through giant pipes beneath the lock chamber. The rate is astonishing. The large lock averages about 2,000 cubic feet per second.
To put that in context, it’s 14,961 gallons per second, or 897,665 gallons per minute.
That can be hard to visualize, though, so the Army Corps gave us even better numbers: 187 average sized bath tubs per second, or 11,220 average sized bath tubs per minute.
That’s a lot of baths. With the tide at 0 feet and the lake level at 22 feet, the lock contains about 10.4 million gallons of water.
As the water moves, the boat slowly descends. The walls around us seem to be getting higher. Once we’re at the level of Puget Sound, the gates in front of us open just enough to let some daylight through the seam. Eventually, another bell sounds and the gates slowly open.
The Puget pulls forward, out of the lock chamber and into the salt water that connects this place to the world.