Divers Map Underwater Caves Beneath City Streets

By Josh Brine

ABC South East SA

Geology

Friday, 24 July 2026, at 7:27 am

Divers use action cameras to create 3D models of underwater caves.

In short:

Divers in SA's south-east use cameras and computers to model underwater caves.

The team hopes the maps will improve safety and give the public a glimpse below the surface.

What's next?

The project's lead hopes the technologies can be used worldwide to map unmapped caves.

The caves and sinkholes on South Australia's Limestone Coast are an underwater wonder.

A project uses cameras to create 3D maps of the region's major sites, giving a glimpse of the caves beneath streets and houses in Mount Gambier.

Advanced cave diver Will Passos used photogrammetry and computer software to recreate dive sites.

Corey Auld, Will Passos, and Chloe Reid after their final dive to map Engelbrecht Cave.

Will Passos said, 'With photography being an interest, this idea came about using photogrammetry to try and map them.'

There are old maps, but it's been a while since anyone updated those maps.

The divers did a trial at Allendale East, with a big camera and not enough lights, and it was a great result.

The divers start at a pool at the bottom of the dry section in the cave's east.

Since the first trial, the method has been refined, resulting in models of several sites, including Pines and Iddlebiddy caves.

Mr. Passos now uses four action cameras, each taking a photo every second, and plenty of lights to ensure the model is accurate.

With a scan of the Engelbrecht Cave complete, Mr. Passos wants to show people how the passages weave under the city's streets.

Mr. Passos can overlay the model on street maps to show how the tunnels run under Mount Gambier.

From primitive to high-tech

In the early days of caving, mapping was a difficult task.

Ian Lewis, who has been diving for about 50 years, said mapping efforts were a response to tragic deaths in the region.

Early efforts were 'primitive', using adapted surface mapping techniques underwater.

Mount Gambier hydrogeologist Ian Lewis has been cave diving for decades.

The team used measuring tapes, underwater compasses, and waterproof notes to map the caves.

They drew the maps on graph paper and measured the angles recorded from the compass.

Mr. Passos attaches four cameras and lights to a rig to take photos for the mapping.

Mr. Passos said he was adapting techniques from other applications.

Photogrammetry is well-known, and the construction industry uses point clouds all the time.

The application is a little different, and the fact that it's underwater makes it even more different.

Not everyone is willing to take cameras underwater instead of diving to record things.

There is a trend globally for divers to use this method because it's not just them who realize there is a gap in information.

Greenfield for exploration

The maps created are now being used by divers, with information available on the Cave Divers Association of Australia website.

The map created using photogrammetry of the Pines Cave.

Mr. Passos thinks about how the modeling could be used to better inform the public, including animations or videos.

The models are really heavy because they're very detailed, so it's always a question of finance.

The modeling has led to the discovery of an extension at Pines Cave, near Tantanoola.

The scans helped identify where to look, which is a great thing.

Curious divers hope to one day dive into one cave and come out another, after discovering an underground tunnel.

Mr. Lewis is excited to see what the technology enables.

Will Passos and the others are at the cutting edge of this.

Mr. Lewis looks back and thinks about their old torches and handling ropes and lines.

It's fantastic what they're doing.

An example of an older map of Engelbrecht Cave.

Mr. Passos wants to look further afield for how this technology can be used, including on unmapped caves across Asia.

When you go overseas, like Thailand, Laos, or Japan, there's nothing.

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