Tupljak: The Flooded Mine

Paws To Peaks
6 hours ago
9 min read

Diving in a flooded coal mine

The tunnel leading to the incline looked fairly comfortable at the beginning. Further inside it became lower and uneven, which made transporting the equipment much harder.

We came to the Adriatic with a plan to dive wrecks.

That was the original idea for the trip.

It turned out that the most interesting place we visited was not a wreck at all, but a mine.

A few kilometres from the coast there is a flooded coal mine called Tupljak. It was the last coal mine operating in Croatia and it was closed in 1998. The mine was still working during the war in former Yugoslavia, and because of that there were different stories and suspicions about what might have been left there underground.

We did not know what we would find underwater.

That was enough reason to take a closer look.

Even as the tunnel became less comfortable, we kept going. Curiosity about what lay ahead - and the growing sense of adventure the closer we got to the water - pulled us forward like a magnet.

First attempts

Before we arrived, two teams had already tried to check the site.

The first team withdrew after a short assessment of the conditions.

The second team managed to lay a guideline to a depth of about 30 metres.

That was where the known exploration ended.

For someone who has never been inside a mine, this kind of dive can be surprising. Underwater you are not moving through a natural cave but through a space designed for people, machinery and transport.

For me there was another aspect to it.

For several years I worked in the fire protection system of a large active coal mine. The layout of tunnels, installations and machinery - and the logic behind their placement - were familiar to me. I had a good idea of what could be expected underground.

That did not make the dive less interesting.

If anything, it created curiosity. I wanted to see how a mine in another country compared to the one I had known from work.

Monika during decompression. This time the visibility was not too bad, so I could finally take a photo of her. In her right hand is the guideline - a thin line leading back home.

The team

All divers involved in the dives were members of GUE - Global Underwater Explorers.

For many years the organisation was associated with the concept known as DIR (Doing It Right). More important in this context is the level of preparation expected from GUE divers when planning and executing complex dives.

Our team specialises in dives conducted in difficult and very difficult environments, including operations carried out to depths of up to 120 metres.

Because of that background, the procedures mentioned in this text are not theoretical guidelines. They are a routine part of how we prepare and conduct dives, and they form the basis of safety when working in places where mistakes cannot be easily corrected. The dives were carried out by Monika, Krzysiek, Andras and Wojtek, with Žarko providing surface support. This team has taken part in many of our underwater adventures over the years.

Carrying cylinders through the access tunnel to the small pool where the dive begins. The easy part of the route ends here.

The way to the water

The car can be left just a few metres from the entrance to the adit.

From there the equipment has to be carried inside.

To reach the water you have to go through more than 200 metres of tunnel. It is not a comfortable walk.

In some places the passage is low and anyone taller than about 170 cm has to stay bent for a good part of the way. The floor is uneven - a mix of stone, concrete and remains of the old mining infrastructure. A transport cart would not help much there.

With a double 12-litre setup and a sensible gas reserve this means several trips with equipment. In total it adds up to more than a kilometre of walking with cylinders.

At the end of the tunnel there is a small pool of water, roughly 3 by 3 metres. This is where the flooded transport incline begins.

https://video.wixstatic.com/video/25bef7_14874f8949d64af4ac51c602f09b2a2a/1080p/mp4/file.mp4

The video is about 10 minutes long. There is no music and no editing for effect - only the natural sounds of the mine, breathing through the regulator, and an occasional word spoken underwater. It is a raw record of the dive: transporting equipment through the narrow tunnel, entering the water, and following the flooded incline down into the mine. If you want to see this place as it really is, this is exactly how we experienced it.

First descent

The incline looked exactly as a mine incline should look.

On the floor there were rails from the system once used to move equipment to the surface. Today that entrance from above is filled in, and access to the incline is possible only through this uncomfortable tunnel, which also partly works as a storm-water channel.

Along the left side ran a water pipe about 200 mm in diameter, with hydrants.

There were hooks for the electrical installation on the walls.

The incline was wide enough for two divers to swim side by side.

To reach a depth of about 65 metres, roughly 250 metres of passage had to be covered.

A short break between dives at the entrance to the Tupljak mine. Once inside, the next stop is more than 200 metres down the tunnel.

The main problem - silt

The biggest challenge in this mine was not the depth.

It was the silt. Much of it was coal dust and underwater it behaved like a curtain, almost cutting off visibility.

The floor was covered with fine sediment. The moment a diver entered the water and began the usual equipment checks, the silt rose immediately and started moving down the incline - exactly in the same direction we intended to swim.

A rough sketch of part of the incline. Drawings like this help during the planning of the next dives, when discussing small details of the plan.

The solution was straightforward.

All procedures in the water were reduced to the minimum.

Most checks were done before entering the water, and the remaining ones while moving down the incline.

The dive started immediately after entering the water.

That allowed us to keep about five metres of visibility on the way down.

The return was usually done in zero visibility.

Planning the next steps after a short reconnaissance and assessing the route for transporting the equipment.

Exploring the incline

The first dive allowed us only to reach the end of the existing guideline and extend it by a few metres. In poor visibility we found two side passages - one was checked, the other looked blocked by collapsed timber and was left for later.

After a short discussion on the surface the decision was simple.

We would return with more equipment.

The second dive brought very different results.

We laid more than 100 metres of new guideline and identified four side passages.

Low water level at the entrance to the flooded incline. The narrow opening leading into the mine is still clearly visible.

After heavy rain the water level rises significantly. It may look better from the surface, but underground it usually means even worse visibility.

Side passages

At 7.5 metres there was a narrow entrance to a side passage right at floor level. At that time it had only about 30–50 cm of height and was blocked with debris. In theory it could be dug open, but that would destroy visibility immediately.

At 14.5 metres there was a small chamber on the right side. It was about 3 by 3 metres with a similar height. You could enter it under the ceiling, but it did not lead anywhere.

At 44 metres there was a much more interesting side passage. It was narrow and dropped steeply downward. Along the walls there were elements of old wooden support.

That was where one of the dives ended earlier than planned.

Only part of the equipment we had to carry to the dive site. The distance one way was more than 200 metres. Each twinset and every single cylinder had to be transported separately - carrying more was almost impossible. That means nearly half a kilometre for every cylinder. Multiply that by the number of cylinders… and yes, we still had the rest of the gear to carry as well. We did quite a lot of walking.

The beam

I was swimming first.

The passage, once used for ventilation, was narrow and low, and its angle was much steeper than the main incline. Monika was a few metres behind me.

At one moment I felt something touch my shoulder - as if someone had placed a hand on it.

That was not an agreed signal, so I started to turn around.

Only then did I understand what had happened.

It was not Monika’s hand.

One of the wooden support beams had come loose and fallen onto me. The water slowed the movement, so nothing serious happened, but it was enough for me to order an immediate retreat.

A collapsing underwater passage is not a place where you want to stay longer than necessary.

Monika approaching the collapsed section of the incline that once led to the surface. During the time the mine was operating, this was the route used to transport equipment.

“Train station”

The most interesting place we reached was a part of the incline at a depth of 64 metres.

We called it “Train station.”

It was the widest section of this part of the mine. The rails formed a junction there and the space looked like a transfer point.

We found:

a mine telephone
a signal board with transport commands

The guideline was finished at an electrical cable junction box. Beyond that point we no longer had enough gas.

In the evenings between dive days I made a few hand-drawn sketches of some parts of the mine. This one shows the “train station” - the furthest point we reached, at a depth of 64 metres.

Conditions

The water temperature was about 14°C.

Visibility ranged from zero to five metres, with an average of about three.

After rainfall the water level in the mine can rise by several metres and visibility deteriorates quickly.

There were also small white shrimp in the water - an unexpected detail in such a severe environment.

Monika checking the equipment before the dive. Careful procedures and disciplined gear checks are one of the strongest aspects of GUE training. Combined with a well-prepared team, it creates a system ready not only to deal with difficult situations, but also to enjoy diving in places like this.

What remained

Down to about 64 metres we were able to sketch a preliminary layout of this part of the mine. Several passages still remained unchecked.

The most interesting area appeared to be the rail junction.

The absence of plans for this section of the mine was both a difficulty and an advantage.

Swimming through a place like that gives a real sense of exploration.

That is something that does not happen very often.

In complete darkness, in the most humid part of the tunnel, we met some unexpected residents - small fungi growing on the damp wood. Likely members of the inkcap family, which often appear in places like abandoned mines and tunnels.

A few words about the mine

Mine passages usually have the shape of a segment of a circle, although in specific conditions they can also resemble a large pipe.

Depending on their purpose they may be only a few metres high or more than a dozen metres. Their function determines their name. A passage closed on one or both sides is called a chamber - a space used for specific tasks such as underground workshops or storage areas.

A vertical passage connecting different levels is a shaft. A passage set at an angle, like the one described here, is called an incline.

Underground transport does not always look like a train with a locomotive, although such systems exist in large mines. On transport inclines there are rails on which transport platforms or mine cars move between levels.

These systems are operated by winding engines (hoists) using a steel cable. Moving down is largely controlled braking, while hauling the load upward requires the full power of the hoisting system.

In large horizontal transport passages, underground trains may operate on fixed routes, carrying miners several kilometres from the shaft to their workplace.

A sketch of the entire incline with the junction we called the “train station.” Also visible is the side ventilation tunnel starting at 44 metres. At 67 metres inside that tunnel, the support beams began to fall on us.

What followed

The dives in the Tupljak mine unexpectedly became the beginning of something larger.

They led us into another chapter of our lives - participation in the Morpheus project, focused on the exploration of Croatian caves.

What followed were dozens of dives in extraordinary cave systems. Places so remarkable that it would be unfair to reduce them to a short mention at the end of a story about a coal mine.

They deserve a story of their own.