Fish Pass at the Upper Outlet
A modern fish passage is being built at the Hochablass in Augsburg, creating ecological connectivity for fish and micro-organisms—an important step toward a healthy Lech River.
A student project team from the Civil Engineering program offers fascinating insights into the planning and implementation of this forward-looking structure.
The focus is on ecological and social issues that demonstrate: Civil Engineering today is far more than just concrete and steel.
The Hochablass, along with the adjacent Kuhsee and the canoeing route, is well known in Augsburg. A fish passage will be built next year for the hydroelectric power plant located beneath the water’s surface. This structure, often colloquially referred to as a “fish ladder,” serves to establish ecological connectivity. Ecological connectivity is essential for establishing a healthy fish population and enables not only fish but also aquatic microorganisms to migrate within the river. These organisms serve as a food source for fish and therefore also play an important role. Ecological connectivity is also required by the European Water Framework Directive (EU-WFD) and has already been implemented at many weirs along the Lech River.
The student project team from the 7th semester of the Civil Engineering program offers an in-depth look at the planning phases. The focus is on the ecological and societal challenges that modern civil engineers must address today—far beyond mere concrete construction. The project is supervised on the university side by Prof. Dr. Hilliges and Prof. Dr. Gattermann; on the client’s side, Mr. Demharter and Mr. Seitz are available as contacts at Stadtwerke Augsburg Projektgesellschaft mbH.
People involved:
Prof. Dr.-Ing. Rita Hilliges
, Prof. Dr.-Ing. Jens Gattermann
, Markus Demharter
As part of their B7 project, the seventh-semester students not only examined the structural implementation but also took a holistic view of the project. The focus was on four key areas that illustrate the complexity of building in the sensitive natural environment along the Lech River: the evaluation of design alternatives, climate analysis, public relations, and long-term performance monitoring.
The Lech River in the Context of Climate Change
The project team analyzed historical flow data and climate projections for the Lech River. The results show clear trends: Water temperatures are rising steadily, leading to lower oxygen levels. This is putting pressure on cold-water species such as trout and huchen.
Why the slot pass won the day
The students examined whether a natural bypass watercourse could be created instead of the planned slotted channel. However, the study showed that such a stream course would have had a massive impact on the park’s tree population and fragmented recreational areas.
A comparison of the options confirmed that the “Vertical Slot Pass” is the preferred solution. This design requires less space, preserves the tree population, and provides optimal flow conditions for the huchen as the keystone species. The decision to proceed with this engineering structure is therefore the more ecologically beneficial solution for the site as a whole.
Building and Construction: Manufacturing Under Challenging Conditions
The construction of the fish ladder poses significant challenges for the construction planning process. The geotechnical project team conducted an in-depth study to determine how the structure could be built under the specific conditions on the banks of the Lech River.
Excavation Pit and Shoring
Since the work area is located directly on the banks of the Lech River and the construction level lies below both the river and groundwater levels, a watertight excavation shoring system is required. The solution: Sheet pile walls around the construction site form a sheet pile box, combined with a dewatering system using vacuum lances. This makes it possible to lower the groundwater level and work without getting your feet wet.
Due to the great depth of excavation, a bracing system consisting of struts and rear anchors was planned. This combination reduces the load on the retaining walls, allows for smaller sheet pile profiles, and minimizes deformation of the system.
Construction Process and Schedule
Another key area of focus was construction scheduling. The geotechnical engineering team divided the project into construction zones and phases and analyzed the timeline for construction. The individual structural components (floor slabs, walls, precast elements) were identified and documented in component drawings.
Special attention was paid to joint design, as the various structural components lead to an increased number of joints. After analyzing various construction options, a hybrid approach combining cast-in-place concrete with strategically placed precast concrete elements was deemed optimal.
The construction schedule developed documents all necessary work steps and logically links them together. The result: a total construction time of about one year—realistic and feasible.
Modern Monitoring: High-Tech Solutions for Functional Testing
Once construction is complete, the crucial question arises: Will the fish use the new route? The project team recommends using a double-chamber fish trap in combination with underwater cameras. This allows for monitoring of fish moving upstream and downstream with minimal injury and stress, while ensuring high system efficiency.
Acceptance Through Communication
Construction sites in public spaces require transparent communication. The project team therefore developed a concept for banners on construction fences that explain to local residents why the work is being done and what environmental benefits the project will bring. Rather than relying solely on “No Entry” signs, the concept focuses on information and transparency.
Practical relevance with immediate impact
For the students, the project offered an opportunity to apply their knowledge directly in a practical setting. It is gratifying that some of the results they produced have been directly incorporated into the current planning process.
Special thanks go to Stadtwerke Augsburg Projektgesellschaft mbH (Mr. Seitz and Mr. Demharter) for providing the project and technical support, as well as to Prof. Dr.-Ing. Rita Hilliges and Prof. Dr.-Ing. Jens Gattermann for their dedicated guidance on behalf of the Technical University of Applied Sciences Augsburg.