Heritage Trails through Dolenjska and Bela krajina

THE SOURCE OF THE RIVER KRKA - KRŠKA JAMA





The siphon lake


The Poltarica spring


The upper reaches of the river




The cavern - the tourist path




Proteus anguinus


Troglocaris anophthalmus


Monolistra spinosa

The river Krka rises in a broad blind valley, at the interface of the Jurassic limestone and the Triassic dolomite formations on the karst plateau north of the village of Krka. The waters rise to the surface at the Pod jamo spring below Krška jama, which is located to the north of Gradiček village. The river is strengthened in its early stages by the small karst streams of Poltarica, Lipovka, Podbukovški and Gabrovški studenec, as well as by the Višnjica stream, the only non-karst stream in the upper Krka catchment,.

The sources of the river Krka, Poltarica and Lipovka streams are fed by water that flows underground from the broad karst hinterland of the Grosuplje basin (Grosupeljska kotlina) and the Rašica underground stream in the Velike Lašče area, whilst the upper course of the river is also fed underground by water from Suha krajina and the Ribnica-Kočevje basin (Ribniško-Kočevsko polje).

The Krka is one of the most interesting karst rivers in Slovenia. It is also the longest completely Slovenian river with a surface length of 94 km. It has a rain and snow run off regime, which gives it a high water mark in the autumn and a low water mark in the summer. The source of the river lies at a height of 268 m above sea level, whilst its confluence with the river Sava at Brežice lies at a height of 139 m above sea level. The average slope of 1.2%, make it one of the quietest rivers in Slovenia. The river catchment covers an area of 2284 km2, which accounts for over a tenth of the territory of Slovenia.

The upper course of the Krka flows in the dinaric direction along the Žužemberk fault, beside which it has cut a picturesque river valley (gorge). This is wider in areas of dolomite bedrock and somewhat narrower in areas of limestone bedrock. There are no surface tributaries in this area, the the river being fed only by numerous karst springs on the river banks.

The Krka is the only river that forms tufa in Slovenia. Its waters are saturated with limestone, which is deposited as tufa from Marinča vas in the upper reaches to Otočec in the middle reaches of the river. It forms characteristic barrages in the upper reaches and broad underwater bands in the riverbed in the middle reaches. Numerous mills and sawmills operated beside the tufa barrages in the past, but the recreational and tourism importance of the river has become increasingly dominant in recent times.

The polution of the watercourses in the karst catchment area has resulted in the pollution of the river Krka at its very source. Thus, the river water in the upper reaches is designated as 2nd quality category of water, whilst the quality in the middle and lower reaches is somewhat lower, falling within the 2nd and 3rd categories. In spite of this, a varied and heterogeneous aquatic flora and fauna distinguishes the river ecosystem. The karst springs are distinguished by endemic subeterranean species, whilst the river itself is inhabited by 38 species of fish.

Krška jama above the source of the river Krka is a horizontal spring cave, from which underground water now only floods out during times of high water. Behind the wide entrance, a homogenous spacious cavern opens out to the north. Its walls are only covered in places by calcereous sinter. It is 200 m in length and up to 30 m in width. It may also be entered through a smaller side entrance in the wall above the main entrance. Regular rock formations and occasional ceiling stones form the ceiling. The floor is covered by rubble and large boulders, which are heaped up to the ceiling in the eastern part. The cavern terminates in a 30 m long siphon lake. The depths of the lake cover the entrance into a labyrinth of narrow underwater tunnels, which reach to a depth of 20 m beneath the water. The siphon tunnel ends after 210 m in a spacious, 60 m long terminal hall. The northern end is closed by large fallen boulders, below which water flows in. The total length of the explored subterranean tunnels amounts to 490 m.

In 1937 the modern main cave entrance was opened wide to facilitate the rapid flow off of underground water and so solve the problem of flooding on the Radensko polje. The bed of the torrential stream was paved with stone slabs and bounded by stone retaining walls.

The Turistično društvo Krka (Krka Tourist Society) organised the cave for visits in 1996. The cave was illuminated, the path to the siphon lake was put in order, an aquarium containing cave salamanders (Proteus anguineus) was installed and the entrance was sealed.

In the second half of the 17th century the polymath J. V. Valvasor was the first person to record a visit to Krška jama. The court mathematician J. A. Nagel examined the cave in 1748, whilst researching and describing the places of natural importance in Carniola at the behest of the emperor. It attracted F. Erjavec a hundred years later. Here he found a previously unknown cave beetle, which he gave to the natural historian F. Schmidt. The first plan of Krška jama was drawn by V. Hrasky around 1887, when he directed regulation works of the river Krka and its catchment in the Radensko polje and the Žalnsko polje.

Krška jama was entered into the Slovenian cave cadaster in 1927, when it was documented by the Cave Exploration Society (Društvo za raziskovanje jam) from Ljubljana. The surprising termination of the promising, but unexpectedly short cave disquieted numerous cavers for a long time. During the 1937 regulation of the main entrance, attempts were made to reach hypothetical new sections of the cave by widening and blasting the narrow Tunnel cleft above the siphon lake. Cave divers have energetically sought the continuation of the cave in depths of the siphon lake since 1994. They have succeeded in diving through the demanding labyrinth of tunnels and have reached the end of the Vrhovec cavern (Vrhovčeva dvorana), where the Krška jama terminates.

The fertile valley of the headwaters of the river Krka was inhabited in the distant past. A prehistoric settlement was located above the Krška jama and the cave itself contains Chalcolithic potsherds (the beginning of the 5th millennium BC). The Turn fortified manor was built on the steep rocky slope above the Poltarica spring in the High Middle Ages. It was first mentioned in the written sources in 1341. In the 17th century the Auersperg family, who owned the manor at this time, built a more comfortable residence on in the valley beside the river Krka. This was the Krka or Vrhkrka country house. The name of the Gradiček village bears witness to the existence of both of the fortifications.

Krška jama was a place of refuge in unsettled times. The local population also fled here during Turkish raids. Local oral tradition states that a half-built church from these times stands in the heart of the cave to this day. The local oral tradition about the Turkish raids was a source of inspiration in the works of the writer J. Jurčič, who came from thevillage of Muljava. He also described Krško jamo in his short story Jurij Kozjak. "… A person, who enters this cave, must crouch down at the entrance. Then he goes down for some time into the earth at an angle of barely 7o. A considerable time passes before he comes to a magnificent hall, which was formed and built by the hand of the Almighty Creator alone…"

The subterranean system of the river Krka, which extends as far as the Šice swallow holes on the Radensko polje, is one of the 20 most biologically diverse subterranean systems in the world. It contains 7 terrestrial and 31 aquatic species of specialised cave fauna.

Individual examples of the Asellus aquaticus cyclobranchialis still have a pale gray coloured body in the Viršnica cave on the Radensko polje, but only their eyes are still coloured in Krška jama. The Proasellus slovenicus, restricted to underground streams in Suha krajina and in the Krka river valley, is a completely blind animal.
The underground catchment area of the Krka is also inhabited by a member of the Niphargus family, the Troglocaris anophthalmus and the Proteus anguinus. The Monolistra racovitzai karamani is a shrimp, which rolls up into a ball like a hedgehog, when danger threatens.

Tiny Velkovrhia enigmatica and numerous tiny snails cling to the rocks in the river current. This is the only known habitat of the Kerkia kusceri and the Acroloxus tetensi with its droplet-shaped shell.

The damp walls outside the water are home to three species of cave snail (Zospeum family). At least three species of beetles also live here; these include the almost centimetre long Typhlotrechus bilimeki and the millimetre sized Bathyscimorphus byssinus. Krška jama is also a frequent refuge for bats, especially the Great Horseshoe bat (Rhinolophus ferrumequinum), although it used to be inhabited by a large group of long-winged bats (Miniopterus schreibersii).

Visits to Krška jame (cave) are possible throughout the year. There is an official carpark near the village of Gradiček, from which leads a 600 m long path to the cave. Guides await you at the Podržaj farm, no. 6, Gradiček,  at the end of the village.