PASCHAL provides robust ATHLET formwork system for flood control
How to better protect Danube-abutting communities against floods? Most importantly, by controlling the most powerful tributaries. The seemingly modest and unimposing river Breg, which converges with the river Brigach at Donaueschingen to form the Danube, comprises a 183 square kilometre catchment area of the Black Forest Nature Preserve, and is therefore particularly susceptible to flooding. An ideal location for the flood control basin was found at the city limits to the west of Wolterdingen. A 110 metre wide, 460 metre long, and up to 18 metre high earth-fill dam is being constructed straight across the narrow Bregtal valley, which will be able to hold 4.7 million cubic metres of water along a length of four kilometres, and on an area of 70 hectares. Flood water flow will therefore be greatly reduced, and the flood level for all communities up to Riedlingen, which lies 130km downstream, decreased.
Centre piece and core of the dam is the hydraulics building with a length of 100 metres, which was – by order of the regional council in Freiburg – constructed in 2007/2008 entirely out of in-situ-concrete by Emil Steidle GmbH & Co KG (Sigmaringen). Its cross section is square and U shaped, whereby the outside walls are 1.75 metres at their base, and 0.80 metres at the top; the insides of the walls are perpendicular, while the outside is slanted inwards at a ratio of 1:20. There are an additional two walls with a thickness of 1.5 metres on the inside in flow direction. These support the powerful lock mechanisms.
At the outflow, the bottom slab slants radially by a couple of metres towards the so called Lake Kolk, while simultaneously broadening to a width of 35 metres into a ‘T’ shape. The overall height of the construction is 19.0 metres. The retaining wall is designed to withstand a water level of up to 16.9 metres. The building is topped with ceilings with a thickness between 0.75 and 0.96 metres.
For the casting pit and diversion flumes, 20,000m³ of earth had to be moved, 7,900m³ of which was topsoil excavation.
The entire pit was then surrounded with subterraneous curtains to a depth of five metres, which were filled with bentonite. This step ensures a drastic reduction of river and ground water influx.
Future plans for the dam also include a by-pass road for Wolterdingen, which means that no additional costly bridge construction will be required.