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

The restoration of tributaries of Cerknica Lake and Škocjan Caves Park
Nataša Smolar-Žvanut 1 , Rok Fazarinc 2 , Borut Perič 3 , Sabina Blumauer 1 , Iztok Kavčič 1
1 Institute for Water of the Republic of Slovenia, Hajdrihova 28c, 1000 Ljubljana
2 Inženiring za vode d.o.o., Pod za Brdom 102, 1000 Ljubljana
3 Škocjan Caves Park, Škocjan 2, 6215 Divača
Schedule:
12.00 Departure from Gospodarsko razstavišče in Ljubljana
13.00 Arrival at the area of Cerknica lake
13.00–14.00 Visit and discussion the restoration of stream Goriški Brežiček
14.45–15.30 Visit the revitalised karst pond (kal) in Lasatke
15.30–16.30 Visit the education trail in the Škocjanski park
16.30–17.15 Short presentation of the Škocjanski park and regulations on land use in
the park, the link between the tourism and nature preservation and
discussion with locals on land use/buying land inside the park
17.15 Departure to Ljubljana
18.30 Arrival to Ljubljana
Figure 1. Locations of the filedtrip.

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

stream in the length of 763 m, construction of drainage ditches, etc. They were draining the
swampy world with partly regulations of the stream Žirovniščica (2000 m), Lipsenjščica
(1074 m), Tresenc (1146 m) and Goričko Brežička (1143 m). Drainage ditches were built in
stream Lipsenj (758 m) and the river channel of Sržen was artificially straightened with the
canal at Ključi (534 m).
Figure 3. Hydrographic network with approximately area of Cerknica lake (Naravovarstveni
atlas, June 2007).
1.2. The aim of the LIFE + project
In 2006 Notranjska Regional Park acquired fnancial support from European programme LIFE
– Nature for project LIFE 06 (LIFE 06 NAT/SI/000069 "Intermittent Lake Cerknica"). The
purpose of this project was the establishment of appropriate conditions for protection and
conservation of animal and plant species and their habitats on Lake Cerknica. Factors that
threaten the biodiversity on Lake Cerknica are modifed watercourses, abandoning of meadow
mowing and defcient knowledge of nature and its conservation.
With the intention of maintaining biodiversity on Lake Cerknica our efforts were oriented to
following actions:
• Restoration of watercourses, that would contribute to higher water ground level and
retaining of overall water level on Lake Cerknica
• Composition of a Management plan, which serves as groundwork for managing the
project area and is orientated towards conservation of natural and cultural heritage of
Lake Cerknica
• Mapping of habitat types with the intention of conserving the endangered ones
• Land managing including buying, late mowing and mulching on the permanently
protected land.
• Popularization of the project and education of the youth on the importance of nature
conservation.
The aim of the project was the restoration of former meanders and by doing so retaining the
water longer in the dry period and increasing the groundwater level in wetland areas. We
expected that in this way the ecological conditions of the wetland areas, and thereby the living
conditions for flora and fauna, improve.

Inženiring za vode d.o.o. produced the project documentation, based on a review of the
situation on the terrain and examining the location of riverbeds as they were before the
regulating operations began. More than 12 km of watercourses in the Cerknica area were
included in the study.
In 2009 restoration of selected watercourses was realized through LIFE+ project. 500m long
parts of Goriški Brežiček and Tresenec streams were carried out. The experiences from this
pilot restoration are needed to perform the restoration of all watercourses of the Lake
Cerknica in the coming years.
Expected results of this restoration:
- slower runoff of low waters from the area of the intermittent lake,
- ground water level rise,
- retention of water in depressions and stream branches, consequently higher constant
ground water level height and change in the soil – water rate.
By increasing length of streams, restoring former branches and meanders, the water surface of
streams increased, which will have a positive effect on the conservation of aquatic, riparian
and wetland habitats.
1.3. Hydrological characteristics of the Goriški Brežiček stream
Due to the nature of the intermittent Cerknica lake, unique hydrologic and hydraulic regime is
characteristic of the whole area. The regulated area is located within reach of the annual flood
waters. Only the upper sections of the Tresenec stream and the Goriški Brežiček stream are
situated on the edge of that area or out of the reach of the frequent flooding. Floods of the
longer return periods inundate the whole area (e.g. in 2000 flood reached 552.05 m a.s.l. and
552.30 m a.s.l. in 1926). In such cases the highest points of the area are under more than 2 m
of water, while most of the area is flooded by 3 meters.
Table 1. Typical flow rates for the period
Stream High water
flow
Mean
annual
flow
m 3 /s m 3 /s m 3 /s
Mean
minimum
flow
Gorički Brežiček 1,7 0,16 0,009
Cerkniščica 64,5 1,2 0,126
1.4. Restoration of the Goriški Brežiček stream
Restoring Goriški Brežiček stream was planned for the entire section, from the mill at the
source, to its mouth in Lipsenjščica River, but only a part has been realized. The entire length
of the stream has been straightened in the past, but given the terrain and vegetation, the
original stream channel is still clearly visible.
Restoring the original layout consisted of its deepening. Average width of the planned
channel section was from 3.0 to 6.0 m. Excavation has been exercised in the form of U, with
banks sloping 1:2, but it was planned that the transition slope of stream bank and terrain on
majority of the length is carried out in a vertical slope and then let the water itself create a

stable bank. We assumed that the stability would be provided primarily by turf and partly by
the riparian vegetation root system.
Deepening of the stream bed at the juncture with the primary bottom at the upstream side has
been protected by the small wooden weir (a small weir with the top corners at the bed level or
just above it, which is not noticeable under normal hydrological conditions). Where possible,
we predicted multiple channels with lower spills/overflows between the excavated meanders.
Figure 4. The Goriški Brežiček stream during the rainfall, January 2007. Straightened,
regulated channel is seen in the foreground, while primary channel is seen in the background
(Photo: Rok Fazarinc).
Figure 5. The Goriški Brežiček stream after restoration, partly flooded, during higher water
surface (March 2010) (Photo: Rok Fazarinc).
Spills/overflows has been fortified with small wooden weirs (wooden piles, tree trunks) to
prevent uncontrolled deepening of the spills/overflows. Spills/overflows were carried out
above medium water level and they were covered with turf. At the appropriate locations at the
contact of the current and planned section, there have also been carried out coves or bays,
which are designed by keeping part of the current channel or in the area of inactive tributaries.

2. ŠKOCJAN CAVES
2.1. The significance of the Škocjan Caves
The Škocjan Caves remain the only natural monument in Slovenia and the Classical Karst
region on UNESCO’s list of natural and cultural world heritage sites. Thus, they hold a
significant position among the world’s natural monuments. The first impression one gets of
the Škocjan karst surface is that it is flat but in fact it is not so. This typical landscape that
developed in limestones is named karst; the word being derived from the name of the area −
Kras.
The entry itself is important from different perspectives: most significantly, that the Škocjan
Caves have gained worldwide recognition and that the state has committed itself to doing
everything in its power to conserve and protect this outstanding natural site.
The preparations for the establishment of the Škocjan Caves Regional Park began in the early
1990s, with the Škocjan Caves Regional Park Act adopted in 1996. A year later, the Public
Service Agency, which presently employs 21 people, began its operation as the Park's
managing authority. In addition to adopting programmes for protection and development of
the park, constantly monitoring and analysing the status of natural and cultural heritage, the
Public Service Agency performs numerous other tasks: it is responsible for the promotion of
the caves, research activity, education, infrastructure maintenance, as well as other activities.
Co-operation with local residents is also important, especially those who are able to benefit
from the park’s establishment.
Figure 6. Škocjan caves park area (Photo: Nataša Smolar-Žvanut)
The rapid development of the area that used to be a demographically and economically
endangered region is reflected in the fact that the Park has obtained membership in various
international institutions, which greatly contributes to the quality economic development both
within the Divača Municipality and the Karst in Slovenia in general.

Figure 7. Škocjan cave with Reka river (http://www.park-skocjanske-jame.si/)
Finally, the park was entered on another list under the auspices of UNESCO: The Ramsar
Directory of Wetlands of International Importance, which includes wetlands which are
important especially as waterfowl habitats. The Škocjan Caves were included in this list due
to their important natural habitat comprising highly specialized and often endemic land and
water cave animal species, among them the endemic cave salamander (Proteus anguinus).
Since 2004, the park is also a part of the Karst Biosphere Reserve network in the frame of the
UNESCO MAB Program.
2.2. Hydrology and description of the caves
Water is one of the essential factors for developing the karst landscape and it is also very
important for life on karst. On Kras, which covers in the hydrological sense the area between
the swallow-holes of the Reka River near Škocjan and the Timava springs near Trieste, this
water is even more precious due to different access, high vulnerability and risk of pollution.
Although the amount of precipitation is rather high (in general the average annual
precipitations are from 14000 to 1650 mm per year) people in this area have always had
difficulties with a good drinking water supply.
The Škocjan Caves are a unique natural phenomenon, the creation of the Reka River. The
Reka River springs from below the Snežnik plateau and flows some fifty-five kilometres on
the surface. Its average discharge between the ponors is 8.95 m 3 /s; during an extremely high
flood it may even reach 387 m 3 /s. After heavy rainfall the river in the cave floods, usually the
swollen water reaches the height of 30 m, the highest known rise in water level was 132 m.
After reaching the Karst, that is the limestone surface, the river not only deepens its riverbed
through erosion, but also by means of corrosion – it dissolves the limestone. In the first part of
its course on the limestone, the Reka still flows on the surface, along an approximately fourkilometre-long
gorge that ends with a magnificent wall under which it disappears
underground. The Reka River blind valley is the largest in Slovenia. In the distant past,
probably in the Early Pleistocene, that is a few hundred thousand years ago, the ceiling of the
cave collapsed some 200 metres from the sinks; as a result, the collapse dolines Velika dolina
(up to 165 metres deep) and Mala dolina (120 metres) were created, separated by a natural
bridge, a remnant of the original cave ceiling. Above the caves, between the wall above the
sink and the walls of Mala dolina, lies the village of Škocjan. Close to the houses, there is

another entrance to the underground, a ninety-metre-deep abyss called Okroglica, which ends
just above the underground Reka River.
At the bottom of Velika dolina, the Reka River finally disappears underground and resurfaces
again thirty-four kilometres away at the springs of the Timava River, not far from the Adriatic
coast. Part of the Škocjan Caves in which the Reka River flows, namely the Šumeča jama (the
Murmuring Cave), is 3.5 kilometres long, between 10 and 60 metres wide and over 100
metres high underground canyon. The length of all cave passages totals approximately 6
kilometres, while the vertical difference between the highest entrance (Okroglica abyss) and
the lowest point in the caves reached by man, that is the siphon, is 205 metres. At some
places, the canyon extends into underground chambers. The largest of them, Martel's
Chamber, is 308 metres long, 89 metres wide on average (reaching a maximum of 123
metres) and 106 metres high, with the highest point of the ceiling at 146 metres above the
Reka River bed. The largest cross-section measures 12,000 square metres, thus giving this
chamber a volume of 2.2 million cubic metres.
2.3. Projects and research activities
One of the most important activities of the park is the encouragement and organization of
research work and participation in it. Following various inventories prepared at the time of
park’s establishment, the majority of activity is oriented towards the renovation of cave
infrastructure and establishment of continuous monitoring, by means of which an adequate
system for monitoring the situation will be established. It is reasonable to monitor all the
parameters over the long term as it will enable rapid detection of negative effects on the
environment and adequate responses or the adoption of certain measures aimed at alleviating
these effects.
For this purpose, different factors are monitored regularly: quality and quantity of water in the
cave, microclimate in the cave, flora and fauna on the surface, cave fauna, cracks in the cave
and on collapse doline walls and the influence of ground-level ozone on the surface.
In order to achieve these objectives, the park regularly participates in invitations to tender
(both internationally and nationally) so as to obtain the necessary funds for the purchase of
equipment, arrangement of infrastructure and the presentation of results to general public. In
addition, some projects foresee the hiring of additional labour needed for project work.
Škocjan Education Trail with museum collections (biology, geology, archaeology,
ethnology and history of cave exploration) supports park educational programme which is
orientated on different target groups. Within this programme many guided tours, exhibitions,
workshops, seminars, events and excursions are organised.
Land use in the park is oriented sustainably. There are some prohibitions about depositing of
excavated material, activities that could change the purposed land use, altering the water
regime, pollution, use of open fire and motor vehicles etc. written in Škocjan Caves Regional
Park Act. Habitats in the park are still well preserved. Polices for the forestry and agriculture
derive from Natura 2000 Management Programme. Some prohibitions are specially written
for the area of natural monuments which are mostly owned by the state. Less than 10 % of the
park protected area (34,9 ha of 413 ha) belongs to Republic of Slovenia the rest is privately
owned.

Figure 8. Škocjan cave viewpoint on education trail (http://www.park-skocjanske-jame.si/).
Other activities
The Public Service Agency manages the park as a public service, provided and partly
financed by the founder. Within the framework of public service, the Agency performs
several activities based on the Škocjan Caves Regional Park Act and the Decision
Establishing the Škocjan Caves Park Public Service Agency. These activities include
maintenance, renovation and protection of monuments and sights in the area of the park;
continuous monitoring and analysis of the state of valuable natural features and cultural
heritage in the park; co-ordination of research tasks related to the park and organization of
research work; participation in international projects; public presentation of the park;
execution and organization of educational activities; preparation and maintenance of paths
and signs in the park; co-operation with the owners of individual monuments in the park;
provision of professional assistance and counselling; maintenance of cave infrastructure for
cave visits and performance of guide services around the Park and caves; and Information
Centre management.
Cooperation with local people
Cooperation with park inhabitants is exemplary and is reflected at all levels of social life,
especially as regards the joint protection of natural and cultural heritage, joint work activities
related to the maintenance and reconstruction of park infrastructure, the mowing and bringing
in of hay and the cultivation of cultural landscape. Of particular significance to the inhabitants
is the assistance provided by the Škocjan Caves Park regarding the preparation of the
necessary documentation related to the activities which affect the environment in the
protected area of the park, joint commemoration of national holidays and local customs and
thus the integration of local inhabitants in permanent and periodic employment opportunities.
The Škocjan Caves Park promotes and in agreement with the Ministry of the Environment
and Spatial Planning (Regulation) financially supports the inhabitants in the park who
renovate their homesteads under the expert supervision of competent services. Part of
renovated homesteads is used for tourist and catering activities, thus providing
accommodation facilities in the park. The visitors thus have the opportunity of staying in the
park more days which enable the local inhabitants to earn additional income. The Škocjan
Tourist Organization is very active in this respect, organizing on a yearly basis in April the
traditional walking expedition along the Reka River sink hole and the festival of local amateur
theatre groups which starts with the performance of choirs on Midsummer Night. The Škocjan
Caves Park participates in such activities both in the preparation and implementation phases.

2.4. Karst ponds
Karst ponds contain practically the only standing waters in Kras. They visibly mark the
cultural landscape and testify to an extremely economical method of using rainwater. In the
regional sense, karst ponds create a network of marine biotopes that are important for the
existence of numerous animal and plant species. Because of their exceptional diversity, caring
for the preservation of every single karst pond is an important contribution to maintaining
biotic diversity.
In our filedtrip the karst pond in Lasatke will be visited, which was revitalised in the process
of Phare project: 1001 karst ponds. It was revitalised in 2006 with contributions of Local
Turist and Sport organisation, Local Hunting Association and The Institute of the Republic of
Slovenia for Nature Conservation and enthusiasm of deceased local biologist Igor Maher.
Figure 9. Karst pons in Lasatke (Photo: Nataša Smolar-Žvanut).
The supply of drinking water has always been a problem in karst regions, and ponds (kal) for
watering cattle were therefore constructed in almost every village, from which water was
originally taken for household use as well. As a rule, the ponds were located in the middle of
villages, at their edges, and only occasionally in the middle of pastures. Natural depressions
were used or basins were dug. These were coated with several layers of thoroughly trampled
clay that held water better than today's cement coating, which tends to crack. The ponds were
always constructed so that rainwater ran into them. If the ponds were located beside fields,
paths, or roads, they were additionally protected with a stone wall to prevent soil from
washing into them. Access to the water was adapted to use by animals, and the ponds were
lined with several ridges to prevent slipping. Cleaning was done during the dry season when
the accumulated mud from the bottom was removed and used as fertilizer. The cattle
themselves helped maintain the ponds since they waded in the ponds while watering and
further trampled the clay, thus sealing any cracks developing on the bottom.
Literature:
Notranjski regijski park 2009: LAYMAN’S REPORT Project LIFE 06 NAT/SLO/000069 Intermittent Lake
Cerknica.
Škocjan Caves Park (http://www.park-skocjanske-jame.si/)
Inžinering za vode 2007: Project on river restoration of strems Goričkui Brežiček and Tresenec.