As of: February 3, 2024, 7:20 a.m
By: Katrin Hager
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At the citizens' meeting in the Gasthof Zur Post, engineer Manfred Schindler (right) answered visitors' questions.
© Thomas Plettenberg
There is no one solution - but there are many small ones: This is the conclusion of the flash flood risk management concept for Warngau.
It became clear at the information evening that a retention basin could only have potential at the Schwarzer Graben.
Warngau
- Whether Ahrtal or Simbach: What heavy rain can do can be seen again and again.
It is often said that one could not have imagined such a magnitude.
That's not right, says Michael Spannring: "If you had done flash flood risk management like this before, you would have been able to detect something like this."
As a civil engineer, Spannring is a specialist in hydraulic engineering and, as a local councilor in Warngau, he made his home community aware of the possibility of state-funded flash flood risk management at an early stage.
Warngau is the first of the municipalities in the district to have applied for it so far and has already received the test results.
The model was presented in July, which shows the flows in heavy rain scenarios for Oberwarngau, Osterwarngau and Lochham.
This is not just about bodies of water that can obviously be overflowing, but also about areas that can only become streams when heavy rain runs off - even worsened by hail.
The next step took place on Thursday evening: Which measures make sense?
Manfred Schindler, doctor of engineering at Dr.
Blasy – Dr.
Overland, presented the investigations to around 60 listeners in the hall of the Gasthof Zur Post.
Retention basins only have realistic potential in one place
The engineering office had examined six possible locations for retention basins in the Oberwarngau area, where larger streams are to be expected from the south during extreme heavy rain, three of them west of the federal highway in the area of the railway line and airport, one east of the federal highway and two on the very eastern outskirts of the area from Dorfbach and Schwarzer Graben.
Ultimately, Schindler comes to the conclusion that at almost all potential locations, a lot of measures would bring little success and that the costs and effort would not be in proportion to the benefits.
Large-scale retention basins that could accommodate the flows from the direction of Schaftlach would cost millions, with no prospect of funding.
And that with questionable benefits: the outflow towards western Oberwarngau would initially be throttled;
However, by the time the building was built, the effect would have been largely dissipated due to lateral inflows.
Schindler only sees realistic potential for one option: his recommendation to the community is to examine a retention basin northeast of the Schwarzen Graben.
A dam height of 6.30 meters would fit in with the topography to some extent, and the intervention would also be more justifiable in grassland.
The sprawling Black Graben poses a potential danger for residents in the Lindenstrasse area and further towards the town center, especially since the Dorfbach cannot accommodate any additional capacity there.
Subsidies for water management could also be included because the measure would help protect against water.
But all of this would have to be examined in more detail first.
“We should take a closer look at this,” said Mayor Klaus Thurnhuber.
Michael Holderer, head of the Rosenheim Water Management Office, did not want to hold out any hope for funding when asked on an ad hoc basis.
Only a mix of small measures helps
Instead of individual major interventions, Schindler recommends a canon of small measures.
Elevated dirt roads could reduce the impact of water flowing towards them.
Private individuals could, for example, limit damage with natural hazard insurance or with structural measures with a manageable investment, such as a light shaft extension starting at around 150 euros or a backwater flap for the sewer connection starting at 400 euros.
Fuel storage and heating systems should be secured, valuables should not be stored in endangered areas or filled sandbags should be kept.
In the event of flooding, it is important to switch off the power and not go into danger areas to fetch something.
Spannring made it clear that the danger of flash floods is not an abstract one: an 80-year-old has a 55 percent chance of experiencing a 100-year flood event over the course of his life, and an 8 percent chance of experiencing a 100-year flood event.
Thurnhuber appealed to use the findings: “In extreme cases, human lives and livelihoods are at stake.”
The presentation
The flash flood risk management concept will soon be posted on the municipality's website, where the river flow analysis can also still be found.