The oldest recorded dams in the mountainous country of Slovakia were built in the 12th and 13th centuries to enable the transportation of harvested wood. However, most of these structures were themselves made of wood, and none have survived to the present day. Evidence remains of of two old dams built for this purpose – Bacúch and Korytnica – but these are of masonry type and are six centuries younger.

Dams for mining purposes

In the 14th century, the mining of gold, silver, copper and iron began in the volcanic mountains of central Slovakia. When the shafts got deeper into the ground, water was needed and not only in order to wash the ore. In the beginning of 18th century, water-driven machines were invented including pumps enabling the de-watering of deep shafts and water-driven hoists, transporting miners into/out of the mines and moving ore. The mines were not only of local importance – their yield in 1740 reached 600kg of gold and 23000kg of silver, plus the yield of copper mines – but 20,000 tons/yr represented 10% of the worldwide copper production in 1770, which placed Slovakia at the top of the world’s copper producers.

The development of this technology required large amounts of water, which needed to be stored in a close location. Dozens of reservoirs were built – many of which were interconnected by tunnels. Because the steep valleys had a relatively small catchment area, water was collected into the reservoirs by canals following the contour-lines of neighbouring valleys. A sophisticated water-management system was established, comprising about 60 dams and reservoirs.

Of these ‘historic’ reservoirs, fourteen are still in operation today – however, they are now used for other purposes, mainly water supply, recreation and fish-breeding. The reservoirs have a total capacity of 4.8Mm3 and the length of the water-collecting canals is 48.3km. The oldest, built in 1510, now provides fresh water supply to the mining town of Banská Stiavnica.

Utilisation of hydro power

Early stages of electricity production

Slovakia’s oldest small hydro power plant was built in 1886 to supply the town of Kosice, in Eastern Slovakia. Until the end of the 19th century, 22 hydro power plants with an installed capacity of 1584kW were in existence, and before World War I, this number rose to 46 plants with a capacity of 13,154kW. Nearly all served industrial plants. Some of them were of ‘mixed’ type – using the hydraulic energy of a water-wheel and producing electricity at the same time. In 1930, there were 108 hydro power plants of ‘mixed’ type, with a capacity of 3838kW, and 56 independent schemes, with a capacity of 13,939kW. In 1943, the capacity of hydro power plants was as high as 22,707kW, producing 130GWh/yr, which represented 18.4% of the total produced electricity at the time.

Hydro potential of rivers in Slovakia

Practically all of Slovakia’s rivers belong to the Danube basin and only about 5% of the surface is drained into the Vistula river. From the 15,530GWh/yr of theoretic hydroelectric potential of Slovak rivers, the technically feasible amount is around 6800GWh/yr.

The distribution of the hydroelectric power among the main river basins and present utilisation is shown in Table 1.

Planning and building large plants

By 1930, there was an elaborate plan for the systematic electrification of smaller towns and settlements by developing the Váh, Slovakia’s main inland river. The first hydro power plant of the Váh cascade was named Ladce and was commissioned in 1935. The outbreak of World War II however delayed commissioning of the second plant, Ilava, until 1946. At the end of the 20th century, there were 35 hydro power plants in operation with a capacity of over 1MW, producing an average of about 4000GWh/yr. However, there still remained around 40% of undeveloped hydroelectric potential.

The ‘golden age’ of utilisation

Construction of reservoirs regulating the flow of main rivers

The systematic development of the Váh river also required the regulation of its flows. Construction of the Orava dam on a northern tributary of the river started during World War II. However, very unfavourable geologic conditions required a change in the design and caused a delay in construction. The reservoir, commissioned in 1953, has a total volume of 346Mm3, which represents over 53% of the annual run-off of the Orava river.

The next multi-seasonal reservoir to be built was Liptovská Mara, on the main Váh river. Built in 1976 it was a similar size to Orava at 360Mm3 (48% of the annual run-off). Both reservoirs were designed to prevent the occurrence of catastrophic floods and assure a satisfactory regulation of flows for the cascade of 16 hydro power plants downstream of the confluence of Orava and Váh rivers.

When development of the Váh river was planned, its utilisation in the future for navigation and an interconnection with the Odra river in Poland and with Elbe in Czech Republic was also anticipated. From a length of about 200km of the planned waterway from the Danube to the town of ˘Silina, there is an 80km long lower section in operation, up to the town of Sered’, where a dam and hydro power plant are planned but not yet realised.

Further multi-seasonal reservoirs were built in eastern Slovakia – Vihorlat on the Laborec river (volume 334Mm3), Vel’ká Domasa on the Ondava river (185Mm3) and Ru ín on the Hornád river (59Mm3) – all tributaries of the Tisa river. All other reservoirs serve only for seasonal regulation, or for transformation of peak flows of peaking hydro power plants. Total volume of the 45 reservoirs built up to now is about 1800Mm3, representing about 14% of the average run-off of all Slovak rivers.

Development of the Váh and other rivers

After World War II, the systematic programme of developing the Váh river as the main source of hydraulic energy for Slovakia was resumed. This – together with the electrification of the country and new industrial plants being built– changed the former rural country into an industrial nation.

From 1946 to 1963 – besides the hydro power plant at the first multi-seasonal reservoir Orava – there were 17 hydro power plants in operation in the Váh catchment area, and a further three in central Slovakia. Their total installed capacity was 565.9MW, with an average annual output of 1533.7GWh/yr. Most of the hydro power plants on the Váh river are in four canal-cascades, usually with three (in one case four) hydro power plants to a canal. Madunice power plant, commissioned in 1960 near the spa Piest’any, is an individual, canal-type hydro power plant, built on very permeable river-sediments in very similar conditions to the Danube. Therefore it served as an experimental project, solving on a smaller scale construction problems expected on the Danube.

The pace of construction (20 hydro power plants in 18 years, or 31.4MW of installed capacity per year) slowed down in the following 14 years (1963 to 1977) to 19.4MW/yr, when besides the second regulating reservoir (Liptovská Mara) only six power plants were commissioned (283.7MW, 179.1 GWh/yr). Three of them were built in eastern Slovakia. In the third construction period (1978 to 1994), when six hydro power plants were built (with 1214.3MW and an output of 2171.1GWh/yr), significant developments were the 664.7MW Cierny Váh pumped storage plant in 1981, and Gabcíkovo hydro power plant, built in 1972 with a capacity of 720MW (note: the energy of the Danube is developed together with Hungary, therefore Slovakia takes 50% of the total, i.e. 439MW and an output of 1875GWh/yr – this project is described later). In the 17 years of the third period of construction, the pace of building increased to an average of 71.4MW/yr. After 1994 no new hydro power capacity was built however, as a result of financial difficulties (detailed later).

Building pumped storage power plants

The first hydro power plant with mixed storage was Dobsiná (built in 1953), with a reservoir on the Hnilec river (a tributary of Hornád) and the hydro power plant on the tributary of Slaná river, in the neighbouring river basin, utilising the relatively large difference in levels – more than 280m over a short distance. Mixed storage was also realised on the hydro power plants Ru ín (1972) and Liptovská Mara (1975), where the installation of reversible Francis turbines enabled a longer peak. The last such project was Cierny Váh, built in 1981 with the upper reservoir at the top of a mountain, utilising the head of 402-434m. The main parameters of these four hydro power plants are shown in Table 2.

Pumped storage plants with peaking hydro power are able to cover outfalls of other sources of energy; they help to take over sudden changes of energy demand and also render regulation services – thus assuring the stability of the electricity system and the quality of energy produced in Slovakia.

Dam building in Slovakia

There are 50 large dams in Slovakia included in the icold World Register of Dams. Most of them are built from local materials – 27 are earth dams and six are of rockfill type. Only six dams are concrete gravity dams and one of them (Orava) is hollow. The rest of the dams are combined earthfill dams with a concrete weir, or take-off structures. Sixteen of the dams are higher then 30m, with three higher then 60m: Nová Bystrica (64m), Ru ín (63m) and Turcek (60m) – all rockfill dams.

In 1960, the first dam in the world with plastic sealing was built in Slovakia – it was the dam of the stilling basin, built in the frame of the Dobisná pumped storage scheme.

The river danube

Only a length of 24.5km (in Bratislava) of the river Danube has both banks in Slovak territory. Upstream, 8.5km is the border section with Austria and downstream of Bratislava, with a length of 141km, there is the border section with Hungary. Nevertheless, the Danube represents one third of the utilisable hydraulic energy of Slovakia.

In the 1950s, the optimal development of the Danube was studied, and it was decided that the common Slovak–Austrian section should be developed by a river-step situated just upstream of Bratislava (at Austrian Wolfsthal), utilising a head of about 10m; while the optimal solution of developing the common Slovak–Hungarian section (head >30m), downstream of Bratislava, comprised a canal step Gab˘cíkovo with a peaking hydro power plant, and the stilling basin should be created by the river-step Nagymaros, situated just upstream of Budapest.

Goals of the Danube development

About 50km downstream of Bratislava, the average inclination of the Danube riverbed suddenly diminishes from 40 to 9cm/km. Around this location, the solid material (gravel and sand), brought from the Alps has been deposited for years and the Danube meandered on the top of its sediments, which gradually grew to a thickness of several hundred metres. The high permeability of these sediments assured an abundance of high quality ground-water, but at the same time created problems in founding hydraulic structures.

People building settlements along the Danube endeavoured to restrict its meandering by building levees on both banks. However, water seeped underneath the levees many times throughout the years, causing breaches by the inner erosion of material. Some of the most recent inundations of protected territory were in 1954 on the Hungarian side and in 1965 on the Slovak side, causing enormous damage. Flood-protection therefore became the most urgent goal of this development. The significance of developing domestic and renewable resources of energy was stressed during the country’s oil crisis in the early and mid 1970s. The Danube Commission recommended an improvement in navigation in the ford sections of the river – upstream of Budapest and downstream of Bratislava – where, in the time of lower flows, navigation was impossible more than half the time.

Last but not least of the reasons in favour of a multipurpose development was as a reaction to the deepening of the river-bed caused by erosion, which increased in intensity during the 1960s when the systematic construction of dams in the Austrian section of the Danube significantly decreased the inflow of solid material. The lowering of water levels also drew down the ground-water levels in the inland delta of the Danube, which started to dry-out; the side arms were receiving flowing water for an average of only 19 days a year. The only way to stop this destructive process was to impound the water-level in the upper section of the river and therefore be able to supply a sufficient amount of water into the side-arms via gravity.

Gabcíkovo-nagymaros hydro scheme

In September 1977, a treaty between the then Czechoslovakia and Hungary was signed for the construction of the Gabcíkovo-Nagymaros hydroelectric system (HES G-N). The system consists of a peaking hydro power plant named Gabcíkovo (with head 16 to 24m and an output of 720MW to produce 2650GWh/yr), situated on the 25.2km long bypass canal and river-step Nagymaros. The scheme also encompasses a run-of-river hydro power plant (head 3 to 9m, 158MW and 1025GWh/yr). The upper section of the Danube is richer in hydraulic energy; therefore, the input into this joint venture’s hydroelectric plant was 55:45, in favour of Czechoslovakia. Also, the amount of works and occupation of territory was greater on the Slovak side. The 1977 Treaty allocated the responsibility of construction in such a way that both sides gained an equal share of works and investment costs (Hungary also became responsible for some of the structures on the Slovak side) and it was agreed to share the produced energy 50:50. The canal, Gabcíkovo hydro power plant and locks are situated fully in Slovak territory and the Nagymaros dam, hydro power plant and locks are fully in Hungarian territory. Nevertheless, the main structures (including the weir Dunakiliti, which should create the Gabcíkovo reservoir) would become common property and the operation costs should also be shared equally.

The international dispute

The construction of Gabcíkovo began in 1978. However, Hungary had problems with assuring the necessary finances, and in 1981 proposed that the project be postponed. When this proposal was not accepted (the top-soil underneath the whole canal had already been removed), Hungary succeeded in concluding a contract with an Austrian firm, which would build and finance the two main structures – Dunakiliti and Nagymaros, getting the costs re-paid in the form of energy from the Hungarian share after commissioning of the project. Work on the Hungarian side started in 1984. The Dunakiliti weir was finished in 1987 and works started on the Nagymaros site.

In 1988, taking into account the pace of works, Hungary proposed to shorten Nagymaros’ construction time by 15 months. This proposal was accepted and the protocol was signed in February 1989. But only three months later, the Hungarian government – under pressure from public demonstrations – stopped work on the Nagymaros site. The environmental NGOs succeeded in persuading the public that Nagymaros endangered the fresh-water supply of Budapest, that its construction would mean that the historic centre of Budapest would be destroyed and that the financing of the construction ruined the Hungarian economy – accusations disputed by the author.

Also, in July 1989 Gabcíkovo was accused of endangering the ecology of the Danube through drying-out, due to the diversion of the majority of flows into the sealed canal (this accusation was made without knowledge about the planned countermeasures, the effect of which would even improve the present unfavourable state, says the author). In November 1989, when Gab˘cíkovo should have already been put into operation, Hungary officially proposed to co-operate with its commissioning – if Nagymaros was abandoned. Yet only two months later, this proposal was also withdrawn.

On both sides of the Danube, the communist regimes were peacefully abandoned and new democratic governments were elected in 1990. In Hungary, those involved in the fight against the ‘Dunasaurus’ (a nicknamed coined by the NGOs opposed to the common development of the Danube) became political representatives. They insisted on abandoning the project, removing all of the structures and returning the territory to its original state – what was quite impossible.

After three unsuccessful negotiations on a governmental level, in 1991 Czechoslovakia decided to ensure the commissioning of the nearly-finished Gabcíkovo by building additional structures in Slovak territory, and to dam the Danube about 10km upstream of Dunakiliti – as shown in Figure 2. The additional structures got the name ‘Variant C structures’ (‘A’ represented the treaty solution and ‘B’ the Hungarian proposal of common commissioning of Gabcíkovo, without Nagymaros).

Gabcíkovo was, after three years of delay, finally commissioned in October 1992. In April 1993, the treaty partners signed a Special Agreement about submitting the dispute to the International Court of Justice (ICJ) in the Hague, with the hope of answering questions about the legality of unilateral steps made by treaty partners.

Solution to the international dispute

Hearings in the Court were held in March and April 1997 and the ICJ issued its verdict in September 1997. According to the verdict :

• Hungary was not entitled to suspend and later abandon in 1989 the works on the common project.

• Czechoslovakia was entitled to proceed in November 1991 with the ‘provisional solution’ (Variant C), but was not entitled to put it into operation in October 1992.

• The notification of Hungary, on 19 May 1992, about termination of the Treaty had no legal effect on the validity of the 1977 Treaty.

• Slovakia, as successor to Czechoslovakia, became a party in the 1977 Treaty.

• Slovakia and Hungary ‘must negotiate in good faith, in the light of prevailing situation and must take all necessary measures to achieve the objectives of the 1977 Treaty, in accordance with such modalities, as they may agree upon.’.

• A joint operational régime must be established and settlement of accounts for the construction and operation of works must be effected, both in accordance with the 1977 Treaty, taking into account mutually agreed modifications,

• If not agreed otherwise, both parties have to compensate the other party with damages, as a result of their illegal conduct.

During the next five months, both parties succeeded in formulating an Agreement to fulfill the verdict, but the 1998 parliamentary elections in Hungary returned the opponents of the HES G-N to power. Their interpretation of the ICJ verdict was that Hungary is not obliged to build Nagymaros – ‘because the Court did not expressively order Hungary to do so’. However, the special agreement did not ask the Court to decide about building individual structures.

In 1999, Hungary offered the solution of fulfilling the ICL verdict, while ignoring the existence of the 1977 Treaty. However, the author believes that this ‘solution’ is in direct contradiction with the ICJ verdict and with the principles of the 1977 Treaty, which – according to the ICJ verdict – remained the main document, regulating future relations of the treaty parties. Years after the ICJ verdict was issued, the treaty parties are even farther from an agreement than they were in February 1998. However, the damages caused by delays in operation grow every year and have already reached billions of Euros. The greatest part of this damage was caused to the economy of Hungary, which spent practically its full share of costs, having absolutely no economic revenue, only to be left with the obligation to pay debts to Austria and to compensate damages caused to Slovakia.

Perspectives on further developments

Construction of fresh-water reservoirs

While southwestern Slovakia has abundant resources of ground-water of high quality, in other regions surface water is the main source of fresh-water supply. At present, 83% of inhabitants are supplied with fresh water from public sources. There exist seven fresh-water reservoirs, with a useful volume of 150Mm3. A further three, with additional volume of 54Mm3, are needed (see Table 3).

Reservoirs and flood-protection

The two main reservoirs on the Váh river assure the flood-protection of the whole Váh valley. The Gab˘cíkovo project significantly increased the flood-safety of settlements along the Danube. All reservoirs built in Slovakia have a part of their volume reserved for mitigation of flood-waves. In spite of this, it is necessary to build polders able to catch and transform flash-floods, which can occur practically anywhere and cause large damage. In 2000 the Slovak government declared a programme of flood protection – but did not include the necessary finances in the state budget. Therefore the programme has onlybeen realised in some places, with the help of foreign grants.

Prolonging the Danube waterway into its tributaries

The prolonging of the Danube waterway into the Váh river was already planned in 1930; however, the concept of inland navigation has developed since. Instead of a raft-shute (7m wide) built at Ladce hydro power plant in the later canal-steps, ship-locks 12m wide were built. To ensure the Vah river could be accessed from the Danube at all flow conditions, the impoundment of the Nagymaros river-step is necessary. This should have been in operation since 1992. Vessels are able to enter the Váh but only at the higher water-level in the Danube. Out-flow of loaded vessels can be helped by creating an artificial wave – by peaking operation of the Králová hydro power plant. The present Váh waterway, leading through the locks of Selice and Králová and up to the end of the reservoir along a total length of about 80km, needs the construction of the Sered’ hydroelectric project, to allow the connection of the existing section of the waterway with the system of bypass canals, up to Ilina. There is only one problem hindering the realisation of this multi-purpose project – the necessary finances.

Optimal utilisation of the hydroelectric potential of Slovakia

After the realisation of the Sered’ project on the Lower Váh river and the Bratislava-Wolfsthal river-step on the Danube, there would remain the possibility of building three cascades of mostly low-head river-steps on the Orava, Váh and Hron rivers :

• Eleven river-steps on the Orava river, with heads 6-8m, with a total installed capacity of 42.8MW and average production of 164.4GWh/yr.

• The lowest hydro power plant Dierová is a peaking one, situated just upstream of the estuary of Orava into the Váh, at a reservoir, with head of 40m, installed capacity of 81.4MW, and generation of 120.2GWh/yr.

• Nine river-steps on the Váh river, upstream of the confluence with Orava, with heads 9-16m, a capacity of 57.4MW and average production of 244.3GWh/yr.

• The missing Strecno hydro power plant and reservoir on the Váh river, upstream of Ilina hydro power plant, with head of 23m, 96.9MW of power and 141.8MW annually.

• Twenty-three river-steps on the Hron river, from its estuary to Banská Bystrica, with heads 4-25m, a total capacity of 84.9MW and average production of 392.5GWh/yr.

The systematic development of just the three main rivers could increase the utilisation of the hydroelectric plant by more then 15%, to over 74%. Besides these hydro power plants, there still remains the unutilised hydroelectric power of further rivers and tributaries, where more then 200 micro hydro power plants can be built, if the financing of these investments could be assured.

Problems with financing

During the previous economic system, the utilisation of hydraulic resources was financed from the state budget. To assure the monopoly of electricity production, hydroelectric projects were artificially divided into two state-enterprises:

• The energy producing one, owning only the upper structure of the hydro power plant, including the technological part – producing practically all revenues.

• All remaining hydraulic structures: dams, weirs, canals, levees etc., which were maintained and operated by the River Authority.

While both enterprises were state-owned, the loss of one enterprise was compensated by the profit of the other – in the frame of the state budget. The payment of the energy-producing enterprise to the water-management one was symbolic – it represented only about 10% of the value of produced energy, while the costs of the hydraulic structures represented 85 to 90% of investment costs of the whole hydroelectric project.

In free market conditions, the state property is now being privatised, consequently drastically reducing the income of the state budget in the future. The state now has no funds left for financing the development of hydraulic and hydroelectric resources. In 1994, the state enterprise owning all power plants was transformed into a shareholding company, which is now being sold to an Italian firm – including all hydro power plants. Since 1994, the state-owned River Authority helped to create profit to a Slovak private company – however, if the sale was to be accomplished, Slovakia would use part of its financial resources to permanently increase the profit of the private Italian company.

There is, of course, a solution. If the hydro power plants were to be excluded from the share-holding energy producing company into a state-owned enterprise, the two parts of Slovak hydroelectric projects could be united and their revenues would – besides covering the operation costs of both parts – create the (now non-existent) financial source, which would be able to provide the necessary funds needed to realise new investments, developing the remaining hydroelectric and hydraulic potential of Slovakia.

Author Info:

The author is Miroslav B. Li?ska, former President of the Slovak National Committee on Large Dams. Email:


Table 1
Table 3
Table 2