Orava–Tvrdosin Water Works System

The water works system is located in the valley of the river Orava, between Tvrdosin and the village of Ustie nad Oravou. Its comprises the Orava Water Work, built in the years 1941-1953 and the Tvrdosin Water Work as the balancing reservoir of the top Orava water power station, built in the years 1972-1977.

Orava Water Work

The Orava water reservoir, created by the dam in Ustie nad Oravou, is the top reservoir in the river Orava, and in respect of the total accumulated volume, it is the second largest dam in Slovakia. The dame is located in a very beneficial morphologic profile, namely below the junction of the Whie and Black Orava.

The purpose of the water work is to improve the flows of the rivers Orava and Vah for energetic purposes, industry, agriculture, for retaining the peaks of floods flows in the river Orava, and for sports purposes and recreation.

Hydrologic Conditions

From the hydrologic aspect it is beneficial that almost the whole basin controlled by the Orava reservoir, is rich in precipitations, the average of which exceed 1,000 mm (in the dam profile 1,024 mm) annually. This is the reason of relatively high specific drainage q–17 l.s_1. km-2.

On the other hand, high deviations in flows represents a disadvantage.

Characteristic Flows in the Dam Profile (see attached table)

Objects of Wate Work

The main objects of the water work are the concrete gravitation dam, the reservoir, the functional object, and the power station with related facilities.

Construction Design of the Dam

In order to ensure stability and non-permeability of the subsoil, a special profile of a gravitation concrete dam was projected, with slight batter of the wall on the water side (1:0.4) and the average slope of the air face (1:0,75) on the air side, resulting in prolonged contact of the concrete block with the subsoil rock on the overall length of 30 to 50 m. In addition to that, before the main blocks in the valley part (where the height of the dam reaches 36 to 47.5 m), prolonged block 20 m long and 6 to 6.5 m high were built, which are covered by a clay layer. These very thorough measures should limit the ingresses, prolong the ingress route, and reduce the horizontal pressure on the main block. The same purpose if followed by a unique design of the grout curtain built from the grout tunnel situated in the prolonged block, it is double-row and in some places, it reaches the depth equal to double the height of heaving (D = 2H)j. The main purpose of this relatively complicated design is ensuring stability against shift slidings in the direction of the water stream.

A special element of the six block in the valley part is the lightening cavity (6 m wide) between the blocks, which is functionally used (between the block 8-9). It contains pumps for pumping ingress waters.

The concrete unit of the dam (gravitation wall) is divided by vertical dilatation joints for 26 block with maximum width 14 m. The sealing of the joints between the blocks is made as triple, by reinforced pentagon, shafts with diameter 40x40 filled by clay and special rubber bands covering the joints. This is a sealing of the dilatation joints of the blocks, which enables mutual movement of the individual blocks up to several milimetres.

Main Parameters of the Dam (see attached table)

Funtional Facilities

For transfer of large water, two top overflows 10.70 + 11.30 m wide, which are dampered by gates 4.3 m high with the capacity of 430 m3.s-1. The overflows are in the 10th and 11th block, where also the other functional facilities are located.

The functional block contains four bottom openings with the diameter 2 m and maximum capacity 240 m3.s-1. The bottom openings are closed on the water side by table by closures, and on the output side by segment closures. The overflows and the bottom openings have the capacity of 670 m3.s-1 and together with two turbines with the flow 2x50 m3.s-1, the total capacity of the functional facilities is 770 m3.s-1.

Water Power Station

The water power station is situated below the dam, behind the block 13 and 14. The below-dam power station uses the height from H = 9.9 m to H = 28.0 m. The power station comprises two Kaplan turbines with the flow 2 x 50 = 100 m3.s-1. Water is led to turbines by two pipings with diameter 4.5 m, which are connected to the inflows, located in the main blocks and pass through the interblock, between the power station a and the embankment. The inflows are blocked by table high-pressure valve gate controlled hydraulically. The draft tube – the outflow from the power station, are blocked by steel block tables.

Between the dam and the power station buildings, there are transformers and the distribution station of 110 kV. The power stations works as a half-peak one, fully automated and equipped by remote measurement and control. (see attached table)

Information & Contact:

Research Institute of Water Management,
Nabr. arm. gen. L. Svobodu 5,
811 02 Bratislava,
tel.: 00421 (2) 59343111,
fax: 00421 (2) 54415743