Originally published on the ECOreport
Bavaria’s Sylvensteinspeicher (Sylvenstein Dam) has two power plants with a combined electrical capacity of 7 MW (26 GWh a year). Andreas Bauer, of the Regional state office for water management in Weilheim, says that while they are happy to produce electricity, this is a byproduct. The earthen embankment dam’s main purpose is to withstand floods, and retain enough water to service the surrounding area’s droughts. This facility has withstood a number of extreme weather events during its 56 year history. The Sylvensteinspeicher, operated by the Regional state office for water management in Weilheim as part of the Bavarian State Ministry of the Environment and Consumer Protection, is an example of how dams can protect us from climate change.
The 200-meter-wide dam was built at the convergence of the Isar, Dürrach and Walchan rivers, about five kilometers from the Austrian border. Six hundred men were employed building it from 1954 to 1959.
“A few government workers living in the village of Fall had to leave their homes,” said Bauer.
Fall’s original site, and the adjoining fields, is now under the reservoir, and a new village was built on higher ground.
There was no provision made for trout, which can no longer swim beyond the dam site.
These environmental issues seem trivial compared to the floods that periodically raged through settlements along the Isar during the years prior to the dam. Even Munich, some 75 kilometers to the north, was not safe.
This ceased to occur after the Sylvensteinspeicher was built. The dam has withstood every flood during its existence. The worst occurred during 1999, 2005, and 2013.
“The maximum inflow, which occurs once in one hundred years, is about 950 cubic metres per second,” said Bauer.
This dam can hold about 125 million cubic meters of water, which is a quarter of Bavaria’s total capacity.
The Drought of 2003
The summer of 2003 was very hot, and reservoir’s surface dropped about 10 meters. There was only 6 meters to the bottom and, towards the Isar River, “the reservoir looked like a desert.”
“We have to guarantee a discharge of about 20 cubic metres per second in Bad Tölz, during the summertime. This would have been impossible without the Sylvenstein,” said Bauer.
The dam has been undergoing retrofitting, with the most modern technology, from 2011-15.
“We had a lack of knowledge about the exact state of the core and the deterioration of the measurement systems. We wanted a new and homogenous sealing element. A new seepage water measurement system,” said Bauer.
The first step was adding a double-faced-cutoff wall, one meter thick and 70 meters deep, for the whole length of the dam. (Click here to watch a video that the contractor, BAUER Spezialtiefbau GmbH, made of this phase.)
In 2013, they used a tunnel boring machine to dig a drainage gallery with a diameter of 2.5 meters.
The third step was installing 54 drainage piles, so the amount of seepage can be measured.
“We now have a sectional monitoring of the whole dam. We are able to get information if a leak occurs and (know) where it occurs,” said Bauer.
He added, “This should all be seen as a prerequisite for the adaption to climate change.”
A Normal Year
“The snow melt normally starts in April and ends in June,” said Bauer.
“There are many many people on the river during the summer months. They use it for kayaking, going by boat, swimming, fishing. There are many many people on the river, which means we have to let water go carefully. When we increase the discharge, we have to make slow steps. 10 cubic metres, 20, 30 …”
This speaks well of its value when such extreme weather events become more normal.
Bauer made no predictions about the future, saying “We will take it as it comes.”
Photo Credits: Andreas Bauer of Wasserwirtschaftsamt Weilheim in front of the second spillway at Bavaria’s Sylvenstein Dam – Roy L Hales photo; Cropped image – from Der Sylvensteinspeicher, Wasserwirtschaftsamt Weilheim, 2009, map on page 6; Higherwater in Munich during the flood of 1899 – Der Sylvensteinspeicher, p 10;In front of the Sylvensteinspeicher after the first snowfall of 2015 – Roy L Hales photo; sign three quarters of the way up the wall shows the high water mark during the flood of 1999 – Roy L Hales photo; Drainage Gallery under the dam – Roy L Hales photo; Reservoir behind the dam, looking towards the Walchan River – Roy L Hales photo