The restoration of tributaries of Cerknica Lake and Škocjan Caves ...

1. CERKNICA LAKE
1.1. Basic characteristics
The Lake Cerknica is an intermittent lake appearing at the bottom of Cerkniško polje. It is
the largest Slovenian turloughs and also one of the most important sites in Europe. It has very
special conditions of the area with big diversity of plants, animals and habitats. In the past,
people wanted to transform the area for their benefit. In order to do that, people have made a
lot of interventions in the watercourses and sinkholes of the lake. All these interventions
caused big changes of the water regime of the lake.
Intermittent lake of Cerknica is not the lake in the true sense of the word, but it is the bottom
of the karst field, which is filled during the autumn rains and usually remain flooded until the
end of spring. The lake is filled in 2 to 3 days and covers about 29 km 2 . Lake inflows are
mostly karst waters which originate in the southern and eastern edge of Cerknica field.
Lake Cerknica belongs to karst region of the Ljubljanica river basin. The karst catchment area
of Ljubljanica River is besides of the Trieste karst classified as one of the classic karst areas
of Europe. One of the most interesting phenomena in this area is definitely intermittent Lake
Cerknica and specific are also streams Pivka, Unica, Ljubljanica and many limestone caves.
Figure 2. The Cerknica lake (Photo: Rok Fazarinc).
Hydrological area of Cerknica Karst Polje with tributaries measures 242 km 2 and two
catchment areas of the Cerknica Lake, Loka and Bloke area, measures 185 km 2 and 47 km 2 .
All together the catchment area of Lake Cerknica with tributaries covers about 474 km 2 ,
which is almost 43% of total Ljubljanica river basin before it flows into Sava River.
In addition to the inflow from the karst catchment area Loka field and Bloke plateau,
Cerknica field has also water inflow of significant quantities of the surface or subsurface
waters. From eastern and northern edge comes the water supplies from streams Lipsenjščica,
Žirovniščica, Martinski potok, Grahovščica and Goriški Brežiček. On the western outskirts of
the field from under Javorniki flows the water through permanent or temporary springs
Tresenc, Otoški Obrh, Mrzlek and through the Vranja cave and Suhodolnica. From the
extreme north-east fringe comes the water supplies of the stream Cerkniščica the only one
with appearance of non-Karst surface watercourse.
In the first half of last century, the water management company made the reduction of sinks
and some siphons, expansion and reduction of underground channels, regulation of the Stržen