Those with a fear of heights, depths and enclosed spaces should not take this tour.

It’s a trip into the empty large chamber of the Hiram M. Chittenden Locks in Ballard.

Not many have gotten to experience standing below the massive 6-story walls or going into the culverts within those walls, where water flows in and out.

No elevator will smoothly take you down or bring you back to the lip. Footing can be slippery.

But, the experience is not unlike what scuba divers and cave explorers have. It’s seeing the unseen firsthand, and this only happens once a year.

These culverts within the walls are 14 feet tall and bring water in and let water out of the large lock. They can only be explored during annual maintenance when they’re empty. (Alan Berner / The Seattle Times)
These culverts within the walls are 14 feet tall and bring water in and let water out of the large lock. They can only be explored during annual maintenance when they’re empty. (Alan Berner / The Seattle Times)

When full of water, the locks move boat traffic between the lower saltwater of Puget Sound and the higher fresh water to the east.

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Standing inside the empty large lock, you wonder if the gates at the east end can hold back the water coming from upstream — from the Cedar River, Lake Washington, Lake Union and the Ship Canal. But they have yet to fail in 102 years.

The lock closed for annual work Oct. 12, drained of 27 million gallons of water, according to the Army Corps of Engineers. That’s more than 40 Olympic-size swimming pools.

The gates of the lock loom large for a person photographing them. Alan Berner / The Seattle Times)
The gates of the lock loom large for a person photographing them. Alan Berner / The Seattle Times)

The entire large lock has two parts. It’s 825 feet long and 80 feet wide. The walls are up to 30 feet thick.

Annual maintenance includes scraping off barnacles — their abrasiveness is harmful to juvenile salmon. Items fallen from boats are retrieved, including cellphones, sunglasses, crab pots and a wedding ring (it was successfully returned to its owner). Sacrificial anodes, which protect submerged metal parts from corrosion and decay, are replaced.

John Ryan’s face and hard hat carry the splatter from the removal of barnacles within the large chamber of the Locks. (Alan Berner / The Seattle Times)
John Ryan’s face and hard hat carry the splatter from the removal of barnacles within the large chamber of the Locks. (Alan Berner / The Seattle Times)

Besides the annual work, crews this year are beginning a longer project to replace the six Stoney gate valves. Named after Irish inventor and engineer Bindon Blood Stoney, the vertical panels are part of the system that controls the filling and emptying of the large lock. They’ve lasted more than a century, since 1917, and their replacements are expected to last another hundred years. They can only be accessed when the 14-foot culverts within the walls are empty.

During the seven-week closure, about 100 stakeholders have taken tours. They included members of the U.S. Coast Guard, commercial fishing interests, water-resource managers and mayors of some local cities.

Using headlamps and flashlight, a tour group makes it way through a culvert within the walls of the lock. (Alan Berner / The Seattle Times)
Using headlamps and flashlight, a tour group makes it way through a culvert within the walls of the lock. (Alan Berner / The Seattle Times)

Appropriately dressed and safety-briefed visitors descend a 6-story scaffold into the empty chamber.

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Down inside, it’s quite a different view of the high walls and gates.

The barnacles on the metal gates form a painterly pattern. They’re sharp, and visitors are advised not to touch them.

Barnacles, soon to be removed, cover one of the metal gates of the large lock. (Alan Berner / The Seattle Times)
Barnacles, soon to be removed, cover one of the metal gates of the large lock. (Alan Berner / The Seattle Times)

Narrow side openings at the base of walls lead into the culverts. Here, workers replacing rebar and guides for the Stoney gates have tight quarters.

When the electrical feed to the work lamps in one culvert fails, tour members are asked to use the lights on their phones. Headlamps worn by some are helpful.

William Dowell, left, with the Seattle District, 
U.S. Army Corps of Engineers, checks out the culvert walls that are contained within the walls of the large lock.
(Alan Berner / The Seattle Times)
William Dowell, left, with the Seattle District, U.S. Army Corps of Engineers, checks out the culvert walls that are contained within the walls of the large lock. (Alan Berner / The Seattle Times)

The locks are an engineering feat, and to explore this hidden aspect would not appeal to everyone. The 6-story climb out caps the tour.

All work is said to be on schedule, and the refilled large lock is expected to reopen to vessel traffic Dec. 3.