3D Sonar Images of Baltimore’s Key Bridge Reveal the Underwater Wreckage in Detail

Hamstrung by poor visibility in Baltimore’s Patapsco River, divers are using sonar to help navigate the underwater wreckage of the Francis Scott Key Bridge.

Clean-up and salvage efforts are underway at the site of the bridge, which collapsed into the river in the early morning hours of March 26, after being struck by the cargo ship Dali, which had lost power. Six construction workers who were filling potholes on the bridge died as a result of the accident.

Three-dimensional sonar images shared publicly for the first time on Tuesday show the “sheer magnitude of the very difficult and challenging salvage operation ahead,” according to the U.S. Army Corps of Engineers, which posted the images on Facebook.

The images were captured by the U.S. Navy’s Naval Sea Systems Command Supervisor of Salvage and Diving. To get a detailed look at the submerged wreckage, officials used a sonar imaging tool called Echoscope—the “world’s highest resolution real-time 3D/4D sonar” technology, according to its manufacturer, CODA Octopus Group.

Sonar works by sending out acoustic signals, which bounce off solid objects. The technologies measure the strength of the return signal, as well as how long it takes to come back, which allows for the creation of detailed maps and imagery.

This technology has been crucial for recovery efforts. As heavy-duty cranes lift away pieces of the mangled bridge, teams of highly specialized divers are hard at work in the river. However, mud and loose sediment obscure their view—crews can see just one or two feet in front of them in the murky water.

“Divers are forced to work in virtual darkness, because when lit, their view is similar to driving through a heavy snowfall at night with high-beam headlights on,” per the U.S. Army Corps of Engineers.

Since they can’t see very well, divers rely on “detailed verbal instructions” from operators who are looking at real-time sonar imagery in vessels above the water’s surface.

“No usable underwater video exists of the wreckage, because as one Navy diver stated, ‘there’s no need to take video of something you can’t even see,’” according to the Facebook post.

Crews must remove the wreckage and the Dali before the Port of Baltimore can fully reopen. Baltimore is one of the nation’s most vital shipping ports, handling more vehicles and agricultural equipment than any other port in the U.S., said Governor Wes Moore at a press conference last week. Reopening the port is “not just about Maryland’s economy. This is about the nation’s economy,” he added.

To allow vessels through safely, the river must be completely cleared of debris. Large container ships might sail just two feet above the river bottom when they’re loaded down with heavy cargo, per USA Today’s Tom Vanden Brook.

But to open the river, crews must contend with a variety of complicating factors. Some of the bridge’s steel components are twisted and tangled under the water. Part of the bridge also collapsed atop the Dali and is pushing the vessel down onto the harbor floor—and in order to remove those pieces, crews first need to lift undamaged containers off the ship, reports WBFF’s Keith Daniels.

The debris is also massive, with some pieces weighing upwards of 4,000 tons. Even the most powerful cranes available can only lift up to 1,000 tons at a time, so officials will need to cut the debris into smaller pieces.

Divers, meanwhile, must be careful to avoid getting cut by sharp pieces of debris while also dealing with strong currents and chilly water temperatures.

So far, crews have been able to open two temporary channels in the river to allow a few “commercially essential” vessels through, according to a Tuesday update from the Baltimore mayor’s office. They’re also planning to open a third.

On Thursday evening, the Army Corps of Engineers announced a tentative plan to open a limited access channel to the Port of Baltimore by the end of April, which would allow traffic in and out, one way at a time. By the end of May, the corps intends to have the port operating at normal capacity.

“While this timeline is ambitious and dependent on a number of factors, setting this goal is critically important for those families that are still waiting to bring loved ones home and the thousands of Baltimoreans and Marylanders who rely on the port,” Baltimore Mayor Brandon M. Scott says in a statement. “Some of the best engineering minds in the world and our most important resources have been made available for this critically important project.”

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Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.