New inspection gate at standard water level
Until now, the reservoir had to be almost completely emptied before maintenance inspections could be carried out because the extraction structure's inspection gate was 5m below the standard water level. The water flow shut-off on the new extraction tower is at standard water level. This allows essential work to be carried out without lowering the water, while at the same time slowing down cyanobacterial growth in summer by varying the height at which the surface water is extracted.
Construction pit and jet-grout bodies by Stump-Franki
Before the civil engineering work began, the water level of the reservoir was lowered by 5m and an access road was built for the drilling equipment, which weighed around 80t. In May 2022, the specialist civil engineering team began constructing the jet-grout bodies to seal off the bottom of the construction pit. The sides of the pit were sealed the following June with around 50 running metres of secant bored pile wall made from piles with a diameter of 1,200mm. The piles had to be securely embedded in the granite bedrock up to 16m below the top edge of the terrain. The upper part of the construction pit was shored in sections with the jet-grout slab as a temporary bracing course, while the lower part was braced on the inside with chording and steel girders. The jet-grout slab was dismantled once the civil engineering work had been completed.
Thermal stratification of reservoir water slows down cyanobacterial growth
The unsightly carpets of bacteria are triggered by plant nutrients such as phosphorus and nitrogen that enter the water from the catchment area. If the concentration is too high, these nutrients, in combination with light, lead to the formation of algae and bacteria, especially on the warm surface of shallow lakes. The remodelling of the extraction structure at the Eixendorf dam is primarily intended to maintain the thermal stratification of the reservoir water. This prevents the warm water on the surface from mixing with the cold water at the bottom of the reservoir and keeps the organic substances that are bound in the bottom sediment from being dissolved in the water.
© Stump-Franki
