Izvor Omble

Useful Information

Location: Put Izvora 48, 20236, Dubrovnik.
(42.675871, 18.136774)
Open: no restrictions.
Fee: free.
Classification: KarstKarst Spring
Light: n/a
Dimension: Yavg=24.1 m³/s, Ymin=3.96 m³/s, Ymax=104 m³/s. A=2.38 m asl.
Guided tours: self guided
Photography: allowed
Accessibility: no
Address: Izvor Omble, Put Izvora 48, 20236, Dubrovnik.
As far as we know this information was accurate when it was published (see years in brackets), but may have changed since then.
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Izvor Omble is a karst spring, which is the source of the Ombla river, which is officially 30 m long and is thus one of the shortest rivers in the world. We are not convinced that it is only 30 m long, it flows into the Mediterranean sea, and the river simply widens and becomes an estuary. It's hard to determine where the river ends and the estuary starts. The former river valley was flooded by the rising level of the Mediterranean after the last Ice Age, and so the Rijeka Dubrovačka (Dubrovnik's River) formed. The geographical term is ria, a coastal inlet formed by the partial submergence of an unglaciated river valley. This is actually a difference to fjords, which were glaciated, hence the vertical walls and the deep floor, which is below the ancient seawater level. In this case the river valley deepened continually, cut by a river which met the sea about 40 km away and 100 m lower. The ria is about 200 to 400 m wide, enclosed by 600 m high hills, and about 5 km long.

The karst spring is a cave resurgence, the opening of the cave forms a portal of the huge passage which is 80 m wide and 40 m high. Only the upper part, about 8 m high, is visible above the water surface, the rest is water filled, and as this passage goes down it becomes a sump after only a few meters. Wikipedia says that the source is actually 15 m below sea level, which is a rather weird way to describe this. There is a cave passage, and as it goes down it is below sea level, and as cave passages go up and down all the time the depth differs.

Now for the outside, the cave opening and spring is located at the foot of a 422-m-high limestone cliff named Golubov Kamen. there is the main spring which is the main passage and several other springs right above, which are only active during times of high production, like snow melt or after heavy rains. The spring is the largest karst spring in Croatia, and one of the largest in the Dinarides. The water level in the spring is 2.38 m, which is artificial, as there is a dam. You remember the length of 30 m? That's the dam, or better the distance from the cliff and cave portal to the dam. It seems the river ends with the dam and below is the ria.

On the left shore of the river is a huge building which is ruined and has no roof. This was a factory which used the power of the spring to power their machines. With the huge amount of water, 2.38 m are enough to generate a lot of energy. This is the reason why Croatia plans to build a hydroelectric power station at the spring. It was never realized though, and we guess that's a good thing.

The drainage basin of the spring is estimated to have 600 to 900 km². That's a rather misleading number, as this is karst, and the water originates from a river named Trebišnjica which flows through KarstPopovo Polje to the north in Bosnia and Herzegovina. The water of the river goes underground in dozens of small ponors along the river bed over a distance of some 25 km. However, not all the water goes underground, and so this is one of those situations where a river bifurcates, and a part of the water flows in one direction and a part in another. As a result, the catchment area is shared between two different rivers.