Kaprun power plant group: emptying the reservoirs

The high mountain reservoirs of the Wasserfallboden and the Mooserboden have a combined storage capacity of 166 million m³ of water and are between 90 and 100 metres deep. They are fed by precipitation and supply the VERBUND Kaprun power plant group.

To ensure safe operation, the reservoirs have to be emptied every ten years or so as stipulated by the Water Rights Authority. This takes place in the winter months at a time of low, natural inflow. When empty, underwater components can be inspected and any necessary maintenance tasks carried out. In consultation with the Austrian National Committee on Large Dams, the timing of the current emptying was chosen so that the waterways for the new Limberg 3 pumped storage power plant can also be connected to the reservoirs. Another important milestone for Austria’s biggest power plant, which will enter into operation in 2025. 

Emptying is ecologically monitored

The officially approved emptying began in December, since when water levels have fallen by around 1.5 metres daily. After reaching the lowering target, the remaining volume of water that cannot be processed in the turbines will be discharged through the bottom outlets in an orderly and monitored way. The emptying also transports around 80,000 m³ of sediment. This results in a visual clouding of the water in the Kapruner Ache and the Salzach. “This standard-compliant emptying will only transport sediment that is stirred up by the natural drag of the water. In a seamless monitoring process, probes in the Kapruner Ache and in the Salzach continually measure the concentration of suspended matter. Our experience helps us ensure that the strict official requirements are complied with and that the ecological structure is protected,” workgroup manager Tanja Janisch-Breuer explains the procedure. Ahead of this, the Klammsee will be lowered by two metres first in order to function as a natural buffer and absorb some of the sediment.  

Fish stocks saved

The fish stocks in the Klammsee and the Kapruner Ache were fished out and saved in collaboration with the fisheries officials. This project is accompanied by an ecological building supervision programme. After completion of the maintenance and project tasks, refilling of the reservoirs will begin in mid-May. Depending on the amount of rain and melting snow, it will take two to three weeks before electricity generation can start up again. The two high mountain reservoirs will be filled to seasonal levels again by later summer.