Flood protection in Forstern: An open bypass for the Hirschbach?

Created: 01/27/2022, 11:00 am

By: Veronica power

Looks harmless, but caused a number of cellars to flood in 2013: the Hirschbach near the war memorial and Hirschbachwirt (in the background), which flows through pipes in this area.

© Vroni power

One focus in Forstern this year is on flood protection.

The cased Hirschbach in the town center is the most critical point.

Forstern

– In a workshop, the Forstern municipal council agreed to address flood protection as a priority this year and, if possible, to implement a measure directly.

100,000 euros have been budgeted for this.

Göran Brandhorst from the Sehlhoff engineering office presented the plans to the council, even if some of them are already outdated.

After all, the flood protection concept is already a few years old.

In 2015, in the wake of the floods in June two years earlier, Forstern, Buch, Ottenhofen, Pastetten and Hohenlinden had a flood protection concept drawn up together.

So far, none of the proposed measures have been implemented, Sehlhoff reported to the municipal council.

Because you need space for flood protection, and that is usually the limiting factor, since there are problems with easements or land acquisition everywhere.

The focal points in the Forstern municipal area are on Wettinger Strasse, in Tading, inpreise village and in Forstern in the area of ​​the Hirschbach, with the latter being the most critical point.

In 2013, 25 to 30 cellars were flooded here, Mayor Rainer Streu (AWG) recalled.

The Hirschbach flows openly from the south to Tadinger Straße opposite the Hirschbachwirt.

From here the water is piped below the road and the following development with two canals.

And precisely these pipes are a dangerous bottleneck.

If they can no longer absorb the masses of water, they find their way along the Hirschbachweg and Am Zehntstadl streets.

In the further course, the commercial area and finally the downstream areas of Pastetten and Ottenhofen are also threatened.

In the original concept, the Sehlhoff office had suggested supplementing this bottleneck with another, larger canal, in which the water should then be routed past the Hirschbachwirt back into the Hirschbach at the end of the town.

Brandhorst now presented another idea.

An open body of water could be created instead of the additional piping.

"That would be a very nice solution," said the expert.

The idea: The village pond is included in the flood protection and the new body of water is completely routed around the buildings in this area.

The existing twin pipes are to be retained.

Simply enlarging them, as Anton Oskar (CSU) suggested, would probably fail due to the proximity to the buildings.

This bypass would be a great advantage for flood drainage, "and you could design the body of water beautifully and make it tangible, with seating for example," said Brandhorst, but immediately conceded: "That's just an idea, because you need a reason for it. And this is exactly where this idea could fail. Mayor Streu reported that property owners and residents had expressed great concerns in previous discussions about an open ditch: "They were not very or not at all enthusiastic. You can't imagine it at all."

Oskar warned: "Then bushes grow again that no one wants to take care of." However, Sehlhoff interjected that a cased ditch also has to be taken care of.

He also emphasized that a piped bypass would be very expensive, as would its maintenance.

However, the expert could not name any costs.

All calculations from the past are no longer up-to-date.

Brandhorst suspected, however, that the measures should hardly depend on the money, but rather on whether they can be implemented or not.

Possible subsidies are between 50 and 75 percent.

Franz-Josef Obermaier (AWG) called the Hirschbach a junction near the church.

"If we have solved that, we have already achieved a lot," he said, explaining that open solutions are fundamentally better than pipes.

The water management office also sees it that way, said Brandhorst, especially since the risk of clogging is greater with pipes.

"An open solution would require a lot of educational work for the property owners," said Streu.

Brandhorst offered to be present at the talks, also to clear up technical concerns.

According to Sehlhoff, smaller and less complex measures are conceivable at the inlets from Tading and Wettinger Straße as well as inpreise village.

Brandhorst spoke of improved flows, a near-natural expansion of water bodies, retention areas or dam solutions, although surface water should not be underestimated.

Flood protection usually means a combination of measures to increase discharge at bottlenecks and retention to absorb peaks: the water body must be able to overflow somewhere.

So if you tackle the bottleneck of the Hirschbach on Tadinger Straße first, since this is the most critical point, you should implement at least one retention measure at the same time.

The office now wants to review the measures again, make new calculations and update the costs.

vam