Große Gaißach: Flood protection measures are expected to be implemented from 2024
Created: 04/26/2022, 11:00 am
The Great Gaißach flows peacefully in its bed.
However, the demolition of the terrain on the impact slope (right bank) clearly shows how high and with how much force this creek can overflow its banks at high tide.
© rbe
The Great Gaißach caused damage during a flood in 2020.
Protective measures are being planned to prevent this from happening again.
Gaißach – The Great Gaißach is a torrent from the mountains.
A flood can have far-reaching consequences.
The plan approval procedure for the planned flood protection structures is to be initiated this year.
Great Gaißach: The water body can become dangerous during high water
Largely shielded from view by dense woodland on both sides of the bank, the Große Gaißach flows from the district of Mühl to the confluence with the Isar.
It is not easy to imagine that this peacefully meandering body of water can turn into a fury in the event of a flood, causing flooding and devastation to the Gaißach Moser saw industrial estate, the residential development and the substation in the south of the Tölz settlement and the too narrowly dimensioned passage under the B 13 threatened.
You can find more current news from the region around Bad Tölz at Merkur.de/Bad Tölz.
In 2020, residential buildings were flooded during the flood
There have been three floods there since 1999, each with almost 50 cubic meters per second, the last of which two years ago provided a small foretaste of what can happen there in a hundred-year flood: The experts calculated that the creek’s catchment area was 37 square kilometers from the Water Management Office Weilheim (WWA) for a discharge volume of 86 cubic meters per second.
During the comparatively harmless flood in August 2020, the weir collapsed below the bridge for draining the Linsesägbach, which flows through the Moralt area and the Tölzer Kohlstatt.
The floods then poured into the adjacent residential buildings next to the bridge.
Planning for flood protection: dyke is to be filled up
Johannes Haas, the responsible project manager at the WWA, explains the plans for flood protection on the lower Große Gaißach, which this summer are to go to the Tölz district office and then to the planning approval process.
Depending on how it goes, Haas expects that the appropriate flood protection structures will not be able to begin “before 2024”.
This is what the plans of the water management office look like: The new protective dyke, which is intended to protect the houses in the Tölz settlement, is drawn in as a red band.
On the left is the existing drain of the Linsesägbach, which is to be filled and drained.
Instead, it is discharged 200 meters upstream through a pressure line (shown in red).
© Graphics: Water Management Office
A 460 meter long and one to three meter high flood protection dyke is to be built on the low-lying, level meadow towards the Tölz settlement;
the soccer field in this area will be moved south into the flood zone.
The bank reinforcements are also to be raised towards the Gaißacher Mosersäge commercial area.
Waters are to be deepened - demolition of the overpass is not necessary
The bottom of the water body is to be successively deepened towards the B 13 overpass (by 1.20 meters in front of the bridge and by 1.80 meters below it).
The bridge is to be refounded and statically stabilized.
It will not be necessary to demolish and rebuild the busy overpass.
The existing weir system below the bridge will be dismantled without replacement, reports the expert from the WWA.
The existing gradient of a total of four meters up to the confluence with the Isar will be "stepped in a stepped manner and streamlined, so that fish and other small creatures can pass through the barrier again in the future".
The photo shows the underpass of the Große Gaißach under the federal highway 13 shortly before the confluence with the Isar: Because the cross-section of the passage is clearly too small for the flow of a hundred-year flood, the bottom of the stream and thus also the foundation of the bridge are to be laid significantly deeper will.
© rbe
And how is the derivation to the Linsensägbach?
"The existing drain at the weir will be filled and drained," says Haas.
Instead, the Alte Gaißach is diverted almost 200 meters further upstream through a pressure line to the existing stream bed of the body of water.
Protective measures were already a topic in the Gaißach municipal council in 2016
As early as 2016, the water management office had proposed planned protective measures for the area where the Große Gaißach flows through the Mühl district to the municipal council.
At the time, Mayor Stefan Fadinger described the necessary cuts in the townscape as a "crass and massive intervention in the property of the residents".
For this reason, this section of the planning was put on hold for the time being and removed from the process.
By Rainer Bannier
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