River segments with hydropower facilities are usually considered as ‘heavily modified water bodies’ under the Water Framework Directive. A natural river continuously carries bed load material downstream, forming gravel and shallow water areas. These structures are important spawning grounds and nursery areas for many species. Barrages disrupt this process by keeping the bed load in the retaining area, which eventually silts up. This is the case for the river Iller (Germany), which is heavily influenced by water power facilities. Between Altusried and Lautrach, four power plants with barrages stop the natural bed load transport of the river.
The riverbanks are steep and mounted with large rocks. Key habitats are still missing for several species that lived in this part of the river before the barriers were present. The barrages already have bypasses to enable fish to pass the barrier. However, they look like stone troughs as well. Therefore, despite the existing fish bypass structures, no natural development of the river banks and the alluvial zones is possible. Bed load insertion plays a key role in the process of establishing these key habitats. However, conventional insertion of gravel (dumping large amounts of gravel) is not very effective and disrupts the environment itself as it implies aggressive excavation and transport of sediments.
The LIFE+ ISOBEL project would continue with the conventional approach at one barrage and demonstrate innovative and environmentally-friendly approaches at two other barrages to revitalise the free flowing parts of the river Iller and its fish bypasses, and to reach the good ecological status of all water bodies requested by the Water Framework Directive. The fourth barrage has a natural bed load contribution and remains untreated as base line. The project’s integrated bed load management system would be accompanied by guidelines for its implementation in rivers throughout Europe. The main added value of the proposed system would be its much higher effectiveness and reduced negative environmental impacts (transport, noise, energy).
The project aimed to:
- Define the ‘good ecological status’ for the targeted water body;
- Establish suitable near-natural varied water structures and create missing habitats for the flora and fauna (e.g. spawning and nursery grounds) by replacing existing rock mountings by flat riverside structures;
- Connect river, river banks and alluvial zones;
- Develop and implement a target-orientated, minimally invasive, bed load management;
- Implement bed load management in a systematic way with protecting structures, which reduce drifting at high water levels;
- Make the ecosystem more robust and climate resilient;
- Evaluate the water structure development, the effects on biodiversity and socio-economic impacts; and
- Develop guidelines to boost replication and transferability of project results.
The LIFE+ - Isobel project demonstrated bed load arrangement and management at four hydropower barrages on the river Iller. Innovative approaches were taken at two sections, while a conventional approach was taken at a third section, and a fourth section was selected for comparison due to the barrage having a natural supply of gravel. The project was thus able to identify the optimum method for revitalising the free flowing parts of the river Iller.
The team first established a set of indicators covering hydrology, morphology, fish, macrozoobenthos, amphibians and reptiles, flora, physico-chemical parameters and costs. These indicators were used to monitor and evaluate actions taken at the selected sites. The monitoring will continue for several years after the project to confirm the results since alpine rivers are subject to fluctuating conditions (monitoring over 10 years is required for reliable conclusions). Nevertheless, the results after the four years of the project support the benefit of the actions. Gravel at the target sections has been found to be more resilient to the impact of floods, which thus reduces the amount of gravel required for refilling, along with cost and transport savings. The populations of macrozoobenthos have also been boosted, with higher fish numbers recorded. The project team has also observed a positive development in the spawning of target species as well as the appearance of new fish species. The biodiversity of the riverbanks has also improved due to measures taken by the project.
Specific results included:
- Achievement of “good ecological potential” at three sections of the river Iller (1 km each);
- “Minimally invasive” bed load management with low CO2-emissions and costs;
- Enhanced bypasses at four water power plants (structural elements);
- Improved biodiversity (development of self-sustaining populations of many endangered species as Hucho hucho, Cottus gobio, Triturus cristatus); and
- Improved climate resilience.
Another key outcome of the project was the creation of steering committee comprising all stakeholder groups, including representatives of the fishery and tourism sectors, water authority officials, Environmental Protection Agency (EPA) staff and nature conservation experts. This consensus-oriented committee ensured the smooth implementation of the project despite the adverse weather conditions and heavy floods. The committee is also ensuring the continued monitoring over the coming years as well as helping develop regulation for bed load management by the Bavarian EPA.
Finally, the project actions are being replicated on the Filzinger Wehr barrage on the same river Iller, as well as to a non-alpine river, the river Danube. The beneficiary is carrying out another project, LIFE CityRiver, which is seeking to prevent deepening beds of the Danube endangering buildings in the city of Donauwörth.
Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).