One river: finding continuity for habitats
Re-establishing river continuity is a key issue for fish, but is also necessary to achieve the objectives of the EU Water Framework Directive.
The need to reconnect rivers to provide access to habitats for migratory species is clear. However, understanding where it will bring the most benefit is the big challenge.
Interruptions to river and habitat continuity are a major pressure on the Danube and its tributaries, and were defined – under hydromorphological alterations – as a Significant Water Management Issue in the Danube River Basin Management Plan. The EU Water Framework Directive (WFD) requires the achievement of good ecological status, which, in addition to traditional pollution parameters also focuses on“biological quality elements”– such as fish.
Assessments undertaken for the 2009 Management Plan identified more than 900 continuity interruptions on large rivers (with more than 4000 km² catchment area) from infrastructure projects for flood protection, hydropower, navigation, among others – out of thousands of continuity interruptions in the entire Danube River Basin. Those continuity interruptions prevent access to habitats and suitable spawning grounds for migratory fish species.
To some extent, all fish are migratory species, and the sturgeon is the most prominent representative of the long-distance migrants. Habitats such as spawning, nursery, wintering and feeding sites have to be in place to secure self-sustaining fish stocks. This means that existing habitats need to be protected, while former and degraded habitats must be restored.
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The largest hydropower dam and reservoir system along the entire Danube is located at the 117-kmlong Djerdap (Iron Gate dam I and II) Gorge, and jointly operated by Romania and Serbia. The Iron Gates dams are the most significant barriers for fish migration.
If fish migration could be established at this point, it would open a stretch of 800 km upstream to the Gabcikovo dam, and would provide migratory fish with access to the Danube and its tributaries within this stretch. Building fish migration aids at this site is a challenge. There is an approximate 30-metre difference in water level at Iron Gate I, and there isn’t much space around the structure of the dam – both problems that cannot be solved easily with standard solutions for fish migration. To find efficient solutions, a specific feasibility study is needed.
Knowing where to begin. Though more than 100 fish migration aids are planned to be built by 2015, the problem can’t be solved at once. To ensure the most effective implementation of these measures, the ICPDR has developed an ecological prioritisation approach for continuity restoration in the Danube River Basin. This approach provides information about where measures would be most efficient ecologically and where they will offer the biggest benefit for fish, letting river managers know where to start first.
“The prioritisation approach is one of the most unique methods where really all the countries committed to improving something,” says Stefan Schmutz, Head of the Institute of Hydrobiology and Aquatic Ecosystem Management at the University of Natural Resources and Life Sciences, Vienna “and this can be used as a template for other catchments.”
The prioritisation index considers factors such as migratory behaviour (with long-distance migrants receiving the most weight), location of the obstacle (with obstacles farther away from the mouth of the river receiving less weight), the length of the reconstructed habitat (to give more weight to river segments that are less fragmented by continuity interruptions) and whether or not the obstacle is in a protected area. It is planned the approach will be updated next year as part of the 2013 update of the Danube Basin Analysis.
The results of the prioritisation assessment show that continuity interruptions in the lower Danube at the Iron Gate dams I and II should be given the highest priority. Within the habitats for long-distance migrants, sites in upstream areas of the basin such as Bavaria should also receive high priority, since these are longer reconstructed habitats within Natura 2000 protected sites. More detailed information on the priority ranking in the whole basin can be found in the Danube River Basin Management Plan, available on www.icpdr.org.
The final decision for any measure, however, is up to the countries and will also have to consider where it is technically feasible to build fish passes or find other solutions, as well as take into account the national priorities for restoration programmes.
Support for state-of-the-art measures. Understanding where and when to build migration aids is half the challenge, but it is vital to make sure such aids actually work. “One of the biggest challenges right now is the lack of data,” says Aleš Bizjak, of the Institute for Water of the Republic of Slovenia.
“Comprehensive research is needed to identify efficient solutions.” River managers need support for the planning, design, construction and operation of fish passes. A guidance document already exists in Bavaria; the Czech Republic is currently preparing such a document and one will soon be finalised in Austria. These guidance documents are useful for not only administrations or consulting engineers, but also the operators of infrastructure facilities by supporting planning for the
investments.
Monitoring fish passes can provide critical information about the effectiveness – or failure – of measures. “Even the experts don’t know the reasons… Is there something wrong with the fish pass, or is that there is not a large enough fish population? One of the main topics right now is how to integrate monitoring results in the planning stage,” says Otto Pirker of Verbund.
In all cases, planning must be done with all stakeholders working together. “The big issue for the Danube Basin is to get the people to understand that fish migration is an essential part of restoring good status,” says Veronika Koller-Kreimer, Head of the Aquatic Ecology Subdivision at the Austrian Ministry for Agriculture, Forestry, Environment and Water Management and Chairperson of the ICPDR Task Group on Hydromorphology.
The ICPDR has had success bringing various stakeholders together to ensure balanced representation of needs for infrastructure projects. The Joint Statement on Navigation and its yearly follow-up meetings, for example, ensure that inland waterway transport projects follow guidelines that protect ecological needs. Furthermore, the ICPDR is currently developing Guiding Principles on Sustainable Hydropower Development, which aim for a similar balance in the field of renewable energy.
Shared habitats, shared solutions. To support river continuity measures, the ICPDR organised a workshop on river and habitat continuity, held in Vienna on 4–5 September. The meeting included members of the ICPDR Task Group on Hydromorphology and the Team of Experts on Hydropower, as well as experts working specifically on the planning, construction and operation of fish migration aids.
The workshop included field trips to three fish migration aids in Austria. “The site visit to the Hydropower Plant Melk was a typical example of where we had to go for a compromise”, ... “Why we came to this decision and how we weighed the advantages and disadvantages – these discussions are a good basis for know-how transfer,” says Pirker.
Providing support for the challenges of river continuity will be an important next step. “We have to support the Danubian countries with the existing experience of other countries to share information on state-of-the-art fish migration aids or where to start restoring continuity,” says Koller-Kreimer. “We have started with this in the working groups of the ICPDR, and we need to continue in the future.”
Sharing experience can ensure that measures in one country are effective for the basin as a whole. “If countries restore continuity, it has to be linked to the activities in the other countries, because the fish don’t stop at the borders,” says Schmutz. “We are dealing with the same ecosystem, the same fish species, and therefore we need strategies that really fit together.”
