A kind of spring cleaning was now needed at Sylvensteinsee. The bank and also the water were cleared of driftwood.
Lenggries - Anyone who drives to Sylvensteinsee will notice the large crane that stands next to the dam. It was necessary to clear driftwood from the reservoir and especially the area near the dam. The work took around ten days and was recently completed.
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The team led by power plant operations manager Andreas Riesch invested 300 hours of work – in the water and on land. “Highest praise to the staff,” says Tobias Lang, who is responsible for the reservoir at the Weilheim Water Management Office. The campaign in this form is necessary every few years. “We rarely do this with a crane,” says Lang.
During floods, the tributaries to the Sylvenstein bring with them a lot of wood
Especially during floods, the tributaries bring a lot of wood into the reservoir. Sometimes entire carpets form on the lake. A lot of things drift into the Walchenarm. There is a chain of trees on which the flotsam gets stuck and is pulled ashore by the employees of the water management office. Then entrepreneurs can pick up the wood.
But not everything ends up in the Walchenarm. Some wood is also drifting towards the dam. If the water level rises during flooding, some of it gets caught in the trees on the bank - and remains there when the level falls again. A lot of things wash up in winter, because in summer a chain of trees demarcates the area in front of the bottom drain through which water is released into the Isar. This chain not only keeps larger trunks and branches away from the whirlpool that forms there, but also boaters or stand-up paddlers. “Smaller wood also finds its way into this area in summer,” says Lang. However, there are also larger tree trunks lurking beneath the surface. Lang calls this wood “torpedoes,” which has been in the lake for a long time and is so saturated with water that it floats beneath the surface. This wood was also pulled ashore from the boat.
100 cubic meters of wood becomes 250 cubic meters of wood chips
There - on the narrow path that leads along the dam - the employees cleared the driftwood with the excavator and loaded it into containers, which were then hoisted to the road by the crane. The whole thing was stored and finally shredded at the junction to the Schronbachtal. The approximately 100 cubic meters of driftwood became 250 cubic meters of wood chips. “That’s about three trucks full,” says Tobias Lang.
Wood is removed for flood safety reasons
However, the amounts of wood that are removed vary greatly. “There are years without any driftwood,” says Lang. During the last major flood in 2013, 2,200 cubic meters of material were removed. But of course that is nothing compared to the amounts of gravel that have to be converted every year because the reservoir interrupts the natural onward transport from the tributaries. Around 80,000 cubic meters of gravel are removed every year, says Lang. “And on average it’s 700 to 750 cubic meters of wood.”
Incidentally, the wood is not removed for aesthetic reasons. “This is also a question of flood safety,” says Lang. If the wood stays in the lake, it could not only get into the overflow structures during floods and hinder the outflow there. It could also cause some damage to the bottom drain and headrace tunnel or the associated systems.