Kölnbreinsperre
Hydroelectric generation in Austria has followed two distinct paths. Power stations were constructed in association with barrages on rivers such as the Danube and in the mountains suitable valleys were dammed to impound water to be used for electrical generation.
The Malta Valley (Maltatal) in the west of Carinthia is known as the Valley of Streaming Waters because of its waterfalls.
It is also the location of one of the three hydroelectric power stations that use the water impounded behind the dam at the head of the valley.
The dam (die Sperre) at Kölnbrein was planned in 1930 but construction did not commence until 1971. It was completed in 1974 and at 200 metres from the valley floor to the crest it is the tallest dam in Austria. When the reservoir is full the surface level of the impounded water is at an elevation of approximately 1900 metres above sea level.
The catchment area surrounding the dam can only provide half the volume of water that can be retained behind the dam at its full capacity, so use is made of off peak electricity to pump water that has been used for electricity generation, back to the reservoir impounded behind the Kölnbrein-sperre. This is a vertical lift of about 200 metres.
To gain access to the site from the end of the original road a construction access had to be built. This was no small feat in itself as the road rises 1000 metres in approximately 14 kilometres with gradients up to 13% in some places. Six tunnels had to be excavated through rock obstructions and these remain as they were originally cut – unlined and unlit. One of the tunnels incorporates a steeply inclined and sharp hairpin bend which is a little unnerving on first acquaintance.
The dam structure is arched both vertically and on plan. It is of mass concrete construction and is founded against the granite gneiss which forms the valley sides. Cement was trucked into the site and the coarse and fine aggregates were produced in a quarry developed as part of the works. I have been unable to obtain information about aggregate size, mix design or method used for transporting concrete from the batch plant to the works but I was advised that the mix included fly ash and ice. Individual pours were limited to 30 cubic metres to reduce thermal affects and cooling pipes using pumped local water (average temperature +3C) were also incorporated to keep the temperature down.
The dam is constructed of 30 columns of concrete blocks with a construction joint in each column in the middle of the dam wall. I understand that all the vertical joints were grouted using a cement slurry. The photograph of the rear face of the dam shows the columns and the joints between the blocks. The photo also shows an accumulation of salt at some of the joints which I believe is the result of the deformation and leakage that occurred when the dam was first filled.
To stop the leakage it was necessary to construct an additional mass concrete structure at the base of the dam on the down stream face and consequently the dam didn’t operate to full capacity until 1993.
During construction it was reported that a maximum wind speed of 200 Km/hour was experienced and wind speeds of 80 Km/hour with rain or snow were not unusual.
The dam is monitored with plumb lines mounted in vertical tubes and horizontally using a laser device between stations at each column joint. The movements recorded to date show that the structure is behaving elastically.
The access road to the dam has allowed a very attractive area to be developed for tourism and it has become extremely popular with hikers.
Its popularity can be judged by the fact that timed traffic lights have been installed to control traffic through the tunnels and the construction of a tourist hotel and several Gasthause.
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John Langdon
Klagenfurt
August 2008.