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Drinking Water Supply from Karst Resources
by Natasa Ravbar
Kras is about 40 km long and up to 13 km wide limestone plateau,
that lies between Trieste bay on the west and southwest, alluvial
Soca River valley on the northwest and flysch Vipava valley
on the north and northeast. Further on the east it is bordered
by Pivka basin, towards southeast by Brkini and the Reka river
valley, only towards karst Cicarija, Podgorski Kras and Materija
dry valley the passage is less noticeable (Kras 1999). It reaches
height from 200 to 500 m above sea level and descends towards
northwest.
As it is mainly made of carbonate rocks, there is no surface
running water and underground water flow prevails. On the north
by the Vipava valley, and on the southwest by the coast, the
Cretaceous carbonate rocks pass into less permeable layers of
the Tertiary marl flysch and limestone, however on the south
Paleocene limestone passes into Eocene flysch. On the southwestern
edge of the plateau, where limestone contacts flysch, waters
from Brkini sink underground. The biggest of the sinking rivers
is the Reka River. When the underground water level is high,
the Raša river, that gets low inflows only from the right side,
uses tectonic fault and periodically runs towards Vipava valley.
Waters are flowing underground towards the Trieste bay. They
reappear in submarine springs under Nabrežina (Aurisina) or
in springs of the Timav river (Civita et al. 1995). Because
these springs are the only large water springs in the area,
in the past they were used for drinking water supply of the
town of Trieste.
Kras is an area, where the cave density is the highest in Slovenia.
But only in some of them several hundred meters under the surface
it is possible to reach the underground water level.
Kras is a typical Slovene border area that was marked by mass
depopulation in the past. Natural possibilities for agriculture
are low, because cultivation is limited to small fields at the
bottom of several karst depressions. Growing is therefore directed
in self-providing agriculture. Wine producing, meat remaking,
quarrying, wood and construction industry are important in the
region.
Kras has large potentials for developing various forms of tourism,
because it is in the hinterland of big coastal cities, among
which the population of Trieste and its outskirts presents a
special potential. Traditional traffic role is also important,
because in the southern part of Kras there is railway connection
Vienna - Trieste, which had more influence in the past. Some
years ago a motorway section Ljubljana - Trieste was also built.
Across Kras there are railway and road connections with Vipava
valley.
The biggest economic problem on the Kras plateau in the past
used to be drinking water supply, which has also been one of
the reasons for the scarce settling of the Kras plateau. Main
resource used to base on collecting rainwater and in some places
it is still the main drinking water resource.
Objectives
As many European regions Slovenia also tries to provide sufficient
amount of quality water to the inhabitants. Population and economy
growth and numerous other socio-economic processes have increased
needs for exploration of potential water resources for an effective
and sustainable use of drinking water.
Objectives of this contribution are to present historical background
of drinking water supply and to show the situation of today.
Final results about the drinking water exploitation in Kras
plateau, gained mostly with karst groundwater pumping, are presented:
water resources, water supply extent and drinking water distribution,
number of inhabitants supplied, quantity and purpose of consumption
data. Furthermore some suggestion for subsequent strategic water
resources planning and management are proposed in addition to
possibilities and limitations of the same.
Traditional Water Supply
Traditional water supply on the Kras plateau used to be based
on captures of rainwater, which was collected in wells, called
“štirna”, or lakes, called “lokve”. For watering the cattle
special puddles, called “kal” were provided. At the end of the
19th century, when the needs for water grew, many villages in
Kras built additional wells.
First aqueduct system was built about 150 years ago for the
needs of the Southern railway connecting Vienna to Trieste.
Every railway station was water station as well, where locomotives
were supplied with water. In Gornje Ležece for the needs of
the steam railway several superficial streams were captured
at the contact of karst with flysch. It was gathered in two
reservoirs, storing more than 20,000 m3 of water. From there
water fl owed into 35 km long pipes by gravitation towards Sežana,
Divača and Prosek (Kraški vodovod Sežana 1998; Rustja 2000).
But at the beginning water was only used for locomotives. Because
of constant growing of needs, the whole system was enlarged
for several times and finally in 1935 an additional reservoir
Draga has been built, pumping water from the Reka river. After
electrification of railway, water needs dropped and aqueduct
system was used for supplying people along the railway.
For strategic needs of the front during the First World War
the Austrian army built the aqueduct network across the Kras
plateau. They drew water from the Hubelj springs and pushed
it from Dornberk in the Vipava valley 375 m higher. Below the
Trstelj Mountain reservoirs were built from where water fl owed
towards Temnica, Kostanjevica and Opatje selo, and the second
branch towards Šibelje, Škrbina, Dutovlje, Tomaj, Šepulje, Grahovo
Brdo and Štore. Only for the needs of army 80 km of the network
were built in a couple of months (Kraški vodovod Sežana 1998).
Defeat of the Austrian army has also stopped the construction
of aqueduct network in Kras. The Hubelj aqueduct was taken over
by the Italian army. Because of extremely high costs of the
compression of water into Kras Italians abandoned this part
of aqueduct and conditions in drinking water supply worsened
until they renovated it and attached additional springs from
under the Nanos Mountain. The aqueduct has not been extended
until after the Second World War.
Fig. 1.: Traditional water supply on the Kras plateau used to
be based on capture of rainwater
(Photo: N. Ravbar)
Fig. 2.: Rainwater has been collected in wells, called »štirna«
(Photo: N. Ravbar).
Drinking Water on the Kras Plateau
According to data of Kras
Water Supply Company the Sežana municipality numbered 23,000
inhabitants in 1976. They were supplied with water from springs
at foot of the Nanos Mountain (8 l/s), from the Hubelj springs
(9 l/s) and from the Brkini stream Padež (12 l/s), which was
not sufficient, especially in summer months, when the needs
were the highest.
But, thirty years ago only 37 of 172 villages with approximately
10,000 people or 48 % of the whole population in the municipality
were connected to this water system. During the summer dry months
this percentage was much lower, because the capacity of water
springs decreased altogether under 20 l/s. Therefore special
preventive measures of saving water and supplying it with cisterns
was introduced.
In the late seventies a lot of hydrogeological and speleological
investigations were undertaken in order to explore caves with
underground water (Krivic 1983; Habic 1984). Some boreholes
have been drilled as well. It has been discovered, that the
groundwater in Brestovica dol, that is about 40 m under the
surface is the easiest to be exploited.
In 1984 the Kras aqueduct system in Sežana that pumped water
in Klariči near Brestovica was built. The Brestovica pipeline
was drawn to Lipa under Trstelj, where reservoirs that already
served an old Austrian aqueduct are used. Network system continues
towards Kostanjevica and Opatje selo on the one hand and on
the other towards Komen, Dutovlje, Križ and Sežana. Later, section
Sežana- Rodik- Kozina was attached.
In 1983 the municipality of Sežana passed a decree about water-protection
zones of the Klarici borehole. In the pumping station Klarici
the pumped water is relatively clean, but still suitable treatment
is necessary. For this purpose construction for treatment of
raw water was realized in years 1997-98 (Kraški vodovod Sežana
1998).
In addition to the karst groundwater pumping also two karst
springs under the Nanos Mountain are captured for the needs
of the Kras plateau drinking water supply. So 30% of whole consumed
water is added (3 to 30 l/s) to the system. The only weakness
of these two springs is, that they dry out during summertime,
when the consumption is the highest. Because of better and cheaper
water providing from the Klarici pumping station water capture
Padež and water station Draga have been abandoned.
Fig. 3.: For the needs of the steam railway several superfi
cial streams were captured at the contact of karst with flysch
(Photo: N. Ravbar).
Fig. 4.: At Gornje Ležece there are two water reservoirs, which
could contain more than 20,000 m3 of water. Picture presents
the south water reservoir at Gornje Ležece that could contain
14,000 m3 of water
(Photo: N. Ravbar).
Fig. 5.: When the needs for water increased rapidly, an additional
water pumping station was built
(Photo: N. Ravbar)
Intensive drinking water supply on Kras started in 1986, when
the primary pipeline across the plateau was finished and renewed.
At that time also the additional network, connecting settlements
without connection to the public network, was built.
In 2003 the public water supply, about 480 km of pipelines,
supplies more than 22,500 people in 116 settlements. The municipalities
of Sežana, Divača, Komen, karst part of Miren-Kostanjevica and
partly Hrpelje- Kozina are supplied. The stage of provision
already reached 92%, which has been quite a success of the past
thirty years. Quantity of 250 l/s of water could be pumped in
three boreholes near Klarici, which is sufficient to supply
also the coastal area in the summer months. The inhabitants
of Kras consume only 50 l/s on average.
But settlements on Kras are very sparsely spread out the rough
terrain and are small by their size. Consequently a long network
of pipelines needs to be constructed to supply a small amount
of people. Long pipelines are not easy to maintain and renovate
frequently. Today more than 40% of the pipelines attain the
age between 30 and 60 years, the rest is younger. Water losses
in the system are nearly 35% due to old network, bad quality
of pipeline, lowering of the ground and other reasons.
Average consumption of water on Kras is 100 l/person/day, which
in comparison to the Slovene average 440 l/person/day is very
low. The biggest consumers of drinking water on Kras are Lipica
stud farm, that uses 58,000 m3 water per year, ham-curing plant
in Šepulje, glue factory and other industry. Though economic
activity consumes one third of the water.
Since 1991 consumption of water decreased rapidly and varies
around 1,3 million m3 yearly. Reasons for decrease of consumption
are numerous, but the most important is certainly a careful
management, because price of water on Kras is one of the highest.
This situation is also due to great decline of the army and
economic activity, which affected numerous firms and industry
in late eighties and nineties.
Fig. 7.: The Kras Water Supply Company regularly supplies the
following municipalities
(Source: Kraški vodovod Sežana 2003).
Fig. 8.: Quantity of sold water between years 1993 and 2002
(Source: Kraški vodovod Sežana 2003). The public water supply
network incorporates nearly 8,500 households. Nevertheless a
great part of the inhabitants partly still gather rainwater.
Quantity of consumed water in households is 880,000 m3 per year.
In summertime, when the wells dry up, consumption of water rapidly
increases. It is estimated, that it is even two times higher
than in wintertime.
Branica is an additional source for local supply, where 0,3-3
l/s is captured. It supplies 100 to 120 households in the settlements
Trebižani, Koboli, Veckoti, Dolanci, Cehovini and Kodreti. From
the local water resources are supplied also the villages in
Vrhe (Krtinovica, Štjak, Bogo, Mahnici, Razguri, Sela pri Stomažu,
Jakovce, Vrabče and Veliko Polje).
Fig. 9.: Sketch of drinking water supply situation in the Miren-Kostanjevica,
Komen, Sežana, Divaca and Hrpelje-Kozina municipalities, SW
Slovenia
Legend: 1. local water supply, 2. public water supply, 3. rainwater
supply or supply from springs, 4. main public water supply network.(Source:
Kraški vodovod Sežana 2003).
Before the Kras and Bistrica network were connected in 1990,
the settlements from Obrov to Kozina in Matarsko podolje have
been supplied from the Bistrica karst spring (Kovacic 2001).
After 1997 only Obrov, Javorje, Tatre and Brezovo brdo receive
water from that spring. Some villages in Brkini (Podgrad pri
Vremah, Ostrovica, Artviže, Slope, Brezovica, Gradišcica, Mrše
and Hotična) are still supplied by local resources. In the villages
in Brkini (Rjavce, Kovcice, Ritomece, Velike Loce, Slivje) people
are supplied with local aqueducts. These local systems have
not been connected to the system of the Kras network yet, because
the existent system provides enough of water.
Without connection to the public network there is still around
2,000 inhabitants in the studied area left. It is necessary
to assure them to have access to the quality drinking water
as well. In some remote settlements with few inhabitants (Senadolice,
Vale, Brje pri Komnu, Lukovec, Plešivica, Brestovica pri Povirju,
Nova vas, Tabor and Golac) or in secluded houses drinking water
supply still bases only on capture of rainwater.
Drinking Water Supply Facing New
Challenges
Since the drinking water supply with pumping underground water
near Klariči has been established, gradually the rest of the
settlements are being connected to the public network. In future
building of pipelines to the villages Brje pri Komnu, Brestovica
pri Povirju, Plešivica, Senadolice, Vale, Lukovec on Kras, to
the villages Golac, Poljane pri Podgradu and Skandaršcina in
the Hrpelje - Kozina municipality and to the villages in Vrhe
is foreseen.
Struggle for water of the people of Kras has always been in
the forefront of their concern. Normal progress in rural economy
and individual cities began after construction of drinking water
network on Kras. Thus also Kras could compete with other Slovene
regions in the second half of the past century. Especially quick
economic growth attained the city of Sežana.
Karst groundwater, which is pumped, is organically polluted
due to its vast recharge area. It is also endangered by contamination
because of unsuitable transport system and hazardous spills
of dangerous substances in its catchment area and dumping in
a direct recharge area. Water capacities of the source are not
yet completely exploited though.
While planning water supply in the studied area in the future
it would be convenient to include numerous local water resources
in connection to traditional way of water supply. Water resources
that have been abandoned in the past century could be refreshed,
thus intensifying a care for environment protection. Qualification
and modernization of local water supply systems, wells and rainwater
tanks could contribute to better quality and quantity of drinking
water at the same time. Eventual rainwater usage for garden
irrigation or car washing, for communal activity (street washing)
or for the needs of farming and purifi ed wastewater usage for
industry (as technological water) is not excluded.
Conclusion
About 10 to 20% of the land area is represented by karst. In
Slovenia 44% of land is karst, so it belongs to the countries
with a considerable part of karst. For karst also numerous very
efficient springs are characteristic, which may supply extensive
areas with drinking water. This is the main reason why karst
in Slovenia and in many other places in the world bears mainly
economic significance. Almost a half of Slovenia is karst and
more than half of the water comes from karst aquifers.
For the time being Slovenia still has enough water resources,
which are of good quality. This is an important heritage that
will play an important role in the future. The experts believe,
that by the year of 2025 already 80 percent of drinking water
will be derived from the karst aquifers (Forti 2002).
Today Kras plateau is not a deserted land, where people lack
water. The hydrological researches have shown, that the storage
of underground water is suffi cient to pump up to 1000 l/s of
water (Krivic 1984). Kras aquifer of today can already supply
more than 170,000 people and presents an alternative source
for drinking water supply of the vast area.
References
Civitŕ, M., Cucchi, F., Eusebio, A., Garavoglia, S., Maranzana,
F. & B.
Vigna, 1995: The Timavo Hydrogeologic system: An important
reservoir
of supplementary water resources to be reclaimed and
protected.-
Acta carsologica, 24, 169-186. Ljubljana
Forti, P., 2002: Speleology in the Third Millennium: Achievements
and
Challenges.- Theoretical and Applied Karstology, 15,
7-26. Bucureti
Habic, P., 1984: Vodna gladina v Notranjskem in Primorskem krasu.-
Acta carsologica, 13, 37-78. Ljubljana
Kovacic, G., 2001: Okoljevarstvena problematika vodooskrbnih
obmocij
obcine Ilirska Bistrica.- Diplomska naloga. Univerza
v Ljubljani, Filozofska
fakulteta, Oddelek za geografi jo, 89 p.
Kras. Pokrajina, življenje, ljudje. Založba ZRC (ZRC SAZU).
Ljubljana 1999,
320 p.
Kraški vodovod Sežana (1948 – 1998). Oskrba naselij s pitno
vodo. 1998.
32 p.
Krivic, P., 1983: Interprétation des essais par pompage réalisés
dans un
aquifčre karstique.- Geologija, 26, 149-186. Ljubljana
Rustja, A., 2000: Najstarejši vodovod na Krasu. Kras, 37, 42-45,
Ljubljana
Contact
Natasa Ravbar
Karst Research Institute,
SRC SASA,
Titov trg 2,
SI-6230 Postojna,
Slovenia
natasa.ravbar@zrc-sazu.si
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