Underground Movement

Remember the cursed swamps of Radensko polje that would just refuse to be photographed from a kite? We persisted – and seems seventh time it’s a charm … Look at that! 🙂

There is so much going on in this kite aerial view of the northern part of Radensko polje, a karst field near Račna some 20 km southeast of Ljubljana.

Radensko polje from the north. In the foreground are the estavelles of Srednice, the meandering channel of Dobravka leads to the Beznica cave on the upper left, and the karst field spreads further to the south beyond the solitary hill Kopanj topped with a church.

Radensko polje – Račna karst field – is a small one, just 4 km long and 1 km wide, but it’s huge considering all its natural wonders; its rivers and sinkholes, estavelles and caves, springs and ponors, crowned with Kopanj, a perfect example of an isolated hill on a karst field (a bonus: the greatest Slovene poet France Prešeren lived here for a couple of years). The geology of this polje – clay sediments on a limestone bed with flood-prone rivers and streams – created a unique wetlands ecosystem supporting a huge number of endangered plants and rare animals. Račna karst field is a landscape park and a protected Natura2000 area.

The main river of the north part of the field is Dobravka that drains the Grosuplje basin. As the river enters the porous karst field, it starts to disappear underground – and it does it in a truly spectacular way.

Usually Dobravka goes dark in Veliko retje sinkhole right in the middle of its channel. But when the rains overwhelm this sinkhole, Dobravka overflows and starts to fill secondary sinkholes named Kote (the largest), Mihovka (the most distant from the main channel) and Panšce. At the time of our visit the waters were receding, and Mihovka sinkhole area that was full 14 days ago was now dry.

Kote, the largest secondary entry of Dobravka into the karst underground, fills up the first and dries up the last. Mihovka was empty, but Kote were still full:

While Mihovka is already dry, the largest secondary ponor Kote (upper left) is still full of water

Kote sinkhole area on the left and Srednica estavelle on the right. The powerlines always make us nervous, but this time we flew really high above them …

When the flood waters overwhelm even these secondary ponors, Dobravka starts to fill a meandering extension of its channel that leads to Beznica cave.

Wildly meandering channel of Dobravka that leads to Beznica cave (just beyond the forest line). It’s only about 600 m in a straight line from left to right on this photo, but the full length of the channel is almost 2 km!

Once or twice a year the water level keeps rising and the cave fills up too. Then Dobravka breaks to the right (east) and onwards to the central part of Radensko polje, flooding everything. This tertiary riverbed filled with hydrophilic plants is clearly visible from a kite. And the waters then flow into Viršnica cave system and move underground towads the springs of river Krka.

But the big star of this kite aerial photography session was a sprawling estavelle called Srednice (“the middles”, for they are right in the middle of the field).

Srednice having the last gulps of early spring waters

An estavelle is simultaneously a spring and a sinkhole – when the waters rise it is a spring; when the waters recede it is a sinkhole; it has no other surface outlets or inlets.

As the estavelles go, Srednice are huge – they cover over 35.000 square meters are up to 10 meters deep. And from a kite we can look straight into its exposed limestone heart 🙂

The limestone bed is exposed in the middle of Srednice estavelle – a couple of meters below the ground a porous limestone

All these natural wonders – a meandering river, sinkholes and estavelles and caves and secondary and tertiary channels etc. – are concentrated in just a small northern part of Radensko polje. To the south around Kopanj hill and the village of Račna there are other rivers, karst springs, estavelles, ponors, and a huge cave system of Zatočna cave, Lazarjeva cave and Viršnica.

Central part of Radensko polje with the isolated hill of Kopanj

So … we are not done with Radensko polje landscape park. It’s a tough place to fly a kite (the surrounding hills create terrible turbulences, and the wind rarely blows straight from the north), but very rewarding. More wonders await our flying cameras, and we will soon come back here for the eighth time !

Kite aerial photos shot with Nikon P330 on the Blue Rokkaku kite.

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