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Andrea Schmidt-Schwonbeck
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Renovation of Rosshaupten Dam
Supervision of work relating to improving the dam’s watertightness

Inros Lackner is responsible for the supervision of renovation work on the dam of Germany's largest reservoir. The Forggensee lake is flowed through by the River Lech, and is located in the Bavarian region of Allgäu, below Neuschwanstein Castle. Great volumes of water from melting snow and heavy rainfall flow into the lake, making it the most significant element influencing the uniformity of water flow, and flood protection, on the Lech. The Rosshaupten power plant, with its two Kaplan turbines, typically generates approximately 50,000 KW of renewable energy from hydropower – enough for about 48,000 households.

Rosshaupten Dam was built in 1954, and creates the head storage reservoir for the Lech power plant chain. The renovation became necessary in order to ensure the reliability of the reservoir’s storage capacity. The client is Uniper Kraftwerke GmbH. At the outset, exploratory geological drilling was carried out and the dam’s permeability was determined by means of water pressure tests. As a result, it was decided to construct a diaphragm wall over the entire dam length of about 150 m, as the main component of the new sealing. To facilitate the installation of the wall, a line of soil replacement drillings with a diameter of 1000 mm was carried out to a depth of 40 m. The diaphragm wall, with a total depth of about 80 m and a width of 1 m, was very demanding for the designers and the construction supervision team, as there is little or no experience to date in Germany with this type of work in such dimensions.