Prepared for the flood of the century
Created: 06/05/2022, 10:30 am
By: Susanne Greiner
The construction site in Holzhausen, where a retention basin for the Singold with a storage area of 42 hectares is being built, looks almost like a bone.
© WWA Donauwörth
Holzhausen - It seems a bit like a bone: The retention basin near Holzhausen, which is intended to protect the five neighboring communities in the neighboring district against flood levels of the Singold (which are also financially burdened) - but is nevertheless being built on an area in the district of Landsberg.
Construction is scheduled to be completed in autumn 2023.
A total of almost 900,000 cubic meters of water can then be dammed – on an area of 42 hectares.
"At the moment we are at the throttle structure," informs Peter Schoder from the responsible water management office in Donauwörth.
It is the structure that actually regulates the outflow, so to speak, the heart of the system.
It will have two openings at different heights: the lower base outlet, through which the Singold normally rushes unhindered, and an opening higher up, the service outlet.
When more water flows in and the throttle outlet is reached, the bottom outlet closes, the water is dammed and then regulated and discharged via the upper, operational outlet.
According to current precipitation runoff models, a damming period of up to four days is assumed, says Peter Schoder.
Of course, the scenario that it will rain for a longer period of time cannot be ruled out per se.
The finished retention basin is then designed for the water volume of a 100-year flood, the so-called flood of the century, "plus 15 percent due to global warming".
There are difficulties mainly because of the "poor subsoil conditions" where the load-bearing layers of soil are very deep, says Schoder.
The ground is boggy and peaty – which is why the 35 pillars with a diameter of 1.3 meters to anchor the choke structure had to be driven ten meters deep into the ground.
A total of 1,500 cubic meters of concrete will be used in the structure, plus 120 tons of steel.
The almost finished dam itself is 740 meters long with a maximum height of five meters.
There is a path for farmers and cyclists at the crest of the dam, which is around four meters wide.
So that the latter can cycle through, there will also be a “small connection” into the forest, Schoder describes.
If the 'housing' of the choke plant is completed as planned in the fall of this year, the hydraulic steel construction will begin.
The two passages are installed using two steel panels, a kind of 'gate', which regulate the outflow.
Finally, in mid-2023, the renovation of the Iglinger Weg will start, including the establishment of a level measuring point and the construction of an operations building.
In addition, the dam should then also be tested.
Finally, renaturation measures and the expansion of cycle paths in the forest follow.
The completion of the construction measures is planned for autumn 2023.
Of course, there was initially resistance to the construction, says Schoder.
This can be seen from the fact that the planning started around 20 years ago.
But that is also understandable if something has to be built for the benefit of municipalities in another district.
Because the municipalities of Großaitingen, Lamerdingen, Langerringen, Bobingen and Schwabmünchen will benefit from flood protection, and they will also pay 50 percent of the approximately 7.6 million construction costs - the other half will come from the Free State of Bavaria.
Schoder warns that it is not yet possible to say with certainty whether these 7.6 million are the last word in wisdom and refers to the development of steel prices.
So far there are still small delivery problems.
The offers were obtained last year and ordered in good time.
However, the work with the municipality of Igling, on whose territory the property is located, is now cooperative.
Mayor Günter Först sees the matter as "pragmatic".
And always be present at the weekly construction meetings on site.