Vienna is intensifying its efforts to safeguard the city against extreme weather events by undertaking comprehensive upgrades to its flood protection infrastructure. By the end of 2026, the retention basins in Auhof, located along the western stretch of the Wien River, will be extensively renovated and expanded, with concrete serving as the primary construction material.

The increasing frequency of severe weather, attributed to climate change, has heightened flood risks across Austria. The significant flooding incident in September 2024, which saw the Auhof retention basins reach full capacity--holding nearly one million cubic meters of water within just two hours--underscored the critical importance of robust flood prevention measures in Vienna.

Modernization of Auhof Retention Basins

The restoration of the historic Auhof retention basins began in January 2024. However, the urgency of this project was amplified after the September 2024 flood. These basins, situated on the boundary between the Hietzing and Penzing districts, are engineered to temporarily store excess water during flood events, releasing it gradually as river levels recede. The Auhof complex consists of six retention basins with a combined capacity approaching 1.2 million cubic meters, forming a crucial barrier that shields Vienna from potential flooding.

Concrete has been a foundational material for flood infrastructure in Vienna since 1899, when it was first used in the construction of the 8.5-meter-high walls of the Auhof basins. Its durability, low maintenance requirements, and water-resistant properties make it a preferred choice for structures such as retention basins, relief channels, dams, and spillways. The original concrete walls, built over 120 years ago, have required minimal repairs, demonstrating their longevity and effectiveness in flood protection.

Comprehensive Repairs and Structural Enhancements

To ensure the long-term stability of the Auhof retention basins following the recent flood, Vienna's water management department initiated an extensive refurbishment project. This involves addressing age-related damages such as voids, cracks, and surface spalling. The basins are being reinforced with an impermeable reinforced concrete lining, using approximately 11,000 cubic meters of concrete, to preserve the historical structures and extend their operational lifespan for decades to come.

The project also includes deepening the basins, raising the weirs and partition walls by at least 50 centimeters, and utilizing advanced hydraulic modeling to optimize retention capacity. Additional improvements comprise the restoration and elevation of six weir thresholds and the partition wall between the retention area and the main river channel, increasing their height by 25 to 75 centimeters across a stretch of 1.2 kilometers. With these enhancements, the Auhof system is expected to withstand flood events with a statistical recurrence interval of up to 5,000 years. The total investment for the Auhof upgrades is estimated at approximately 30 million euros, with completion targeted for late 2026.

Concrete's Ongoing Contribution to Urban Flood Defense

Concrete remains integral to other flood control and infrastructure projects in Vienna. For instance, the Wiental Canal is undergoing significant strengthening, with 43,000 reinforced concrete segments being installed along its 8.6-kilometer length to bolster the sewer system's resilience during heavy rainfall. These upgrades are scheduled for completion by mid-2026 and are part of a broader strategy to improve the city's flood defenses.

Balancing Infrastructure with Environmental Stewardship

In addition to their technical function, the Auhof retention basins support valuable habitats for local wildlife. During periods of low water, these basins form the largest wetland in western Vienna, fostering natural environments for species such as beavers, muskrats, otters, and around 120 bird species, including kingfishers, black storks, and various reed warblers. The latest renovation efforts include the creation of amphibian ponds and the installation of bat boxes, further enhancing biodiversity in the area.

By prioritizing both flood protection and ecological preservation, Vienna demonstrates a comprehensive approach to urban resilience in the face of climate change. The ongoing upgrades to the Auhof retention basins and related infrastructure projects underscore the vital role concrete plays in ensuring the safety and sustainability of the city's flood defenses.