River continuity


 For the EU Water Conference 2018, the EC provided a background document, ‘Restoring our Rivers’. This report and its conclusions suggested that river continuity has not been viewed as a significant issue thus far.

However, there are many ongoing and finished projects concerning restoration of river continuity, but the (best) practices part of river continuity restoration and the dissemination of such restoration measures is still underexposed.

The topic river continuity can be seen from different perspectives, like:

  • Fish migration restoration
  • Adaptive management of barriers
  • (National) policies and strategies of improving river continuity
  • River continuity and hydromorphology
  • River continuity and floods & droughts
  • Adjusting barriers or mitigate / compensate for opening up migratory fish habitats.
  • Dam removal

The Policy Brief of the FP7 REFORM (Restoring Rivers for Effective Catchment Management) Project, states that in most EU Member States, the consideration of physical processes remains the main gap in hydromorphological assessment methods. There is a need for more comprehensive process-based hydromorphological assessments that consider the character and dynamics of river reaches and how these are affected by present and past natural and human-induced changes within the catchment as well as the reach (Belletti et al 2015[1]).

The I.S.Rivers 2018 conference in Lyon featured two ECRR workshops. One on river continuity as part of the programme and another one on the integral river basin connectivity. The key conclusions from these workshops were:

  • Concern for the impact on river continuity of both low-head weirs and high dams, with in particular:
    • Evidence of impact of low weirs on non-migratory-fish movement and habitat accessibility.
    • Evidence of impact of high dams on the whole fish community.
  • Concern about the importance of longitudinal hydromorphological continuity, in particular:
    • Importance of combining stakeholders’ interest with hydromorphological changes approaches.
    • Evidence of positive hydromorphological effects from lowering dams in in incised rivers.

River science is being challenged to provide knowledge and greater evidence for discussions and stakeholder engagement in the river continuity decision-making process in many countries.

The French Agency for Biodiversity recently  undertook in 2018 a survey of ECRR members on river connectivity restoration best practices, and the availability of river connectivity national, policies, strategies, plans and approaches. The survey revealed that there were few policies, strategies, plans or programmes on river continuity restoration across these countries. ECRR’s view is that whilst there is a considerable body of evidence and a range of benefits, there is in most countries still no integrated programmed approach to river continuity restoration. ECRR has chosen river continuity restoration as a guiding theme for its promotion plans and supporting activities.


River continuity :

River continuity refers to the possibility for water, sediments, aquatic fauna to pass freely in the upstream and downstream directions along the river (longitudinal continuity) and laterally with the floodplain (lateral continuity) and in a vertical direction (from river interstitial area and groundwater). Any manmade barrier in a river can disrupt this river continuity by fragmenting the river corridor and fluvial habitats. This fragmentation alters  exchanges and passage within the river corridor and river connectivity  on which depend ecological processes.  As result the diversity of habitats and biota can be modified or reduced.  

River continuity restoration :

To restore river continuity, removal of these barriers is the most efficient solution to increase exchanges and passages within the river corridor. Others solutions specially for longitudinal continuity can reduce the impacts of the barriers  by putting in place fish passes to target fish migration, or temporary solutions such as managing hydraulic structures  or water resources.


Refers to any transversal structure which creates a barrier or obstacle as explained above .

Support for river continuity restoration.

In Western Europe, WFD has a positive effect on hydromorphology and river continuity as it has raised its importance at a national level. In France there has been national legislation for river continuity since 2007 and an increasing number of hydromorphology restoration projects have been carried out the past 15 years. Within the UK, hydromorphology is a key driver for assessing GES/GEP and restoration of this underpinning element to support the key indicators of GES.  Most of Scotland’s rivers have been hydromorphologically assessed, on which the decision of prioritising catchments for WFD investment is made. Hydromorphology is also now more integrated with the Floods Directive. For example, flood risk management of structures (weirs, dams, culverts, etc.) – continuity and flooding being seen as interlinked in urban situations.

In the north, in Sweden, the WFD has raised awareness of the critical importance of the need for river continuity. It increased the understanding of water in nature conservation. Demonstrated by the proportion of new water related LIFE projects. In Norway the WFD has helped to increase attention to the issue of river continuity, and has already resulted in an acceleration of the number of measures being implemented: revision of hydropower licenses, improvement of culverts under road crossings (including a handbook), and the reopening and restoration of urban rivers.

In Mediterranean countries, e.g. Spain, river connectivity is one of the most important issues of river restoration for the 2016-2021 planning cycle. The projects are mainly to improve connectivity interrupted by dams, weirs and other obstacles. There is also a wide range of dam removal projects. The NGO’s Wetlands International European Association and CIREF have collaborated to define the criteria to assess before removing dams, focussed on invasive species. This is reported in a set of guidelines for decision-making. Improving river continuity is also high priority in Italy. But, at the same time, in some parts of the country extensive river narrowing and incision problems due to gravel extraction and protection works since the 1940 are using engineered ‘check dams’ as an appropriate ‘restoration’ measure (working with river processes to initiate aggradation). Whilst introducing barriers, this activity combines the appropriate understanding of hydromorphology with necessary engineered structural changes.

For Eastern Europe, there are still issues around the assessment of hydro-morphological impact: for biological elements; in relation to infrastructure projects; in applying Art 4.7 screening; for criteria and data needed; and when dealing with ephemeral rivers.

Dam and barrier removal

There is growing attention on removal of dams (Dam Removal Europe) for river continuity restoration. It is also clear that not all dams can, or have to be, removed because many have important functions required by society, including hydropower production, water supply and water safety.

The focus is on obsolete structures and those with limited use for society where they mostly act as a barrier for water, sediment and river biology. In most cases the removal of obsolete dams is a viable solution for river restoration. Barrier removal restores local river morphology and results in a return to natural functioning for sediment dynamics and river wildlife. No other mitigation measures, for example fish passes, can do this. This can lead to the rapid restoration of fauna and flora that have been suppressed since the structures in question were first built.

ECRR’s view is that there is a need to integrate the issue of dam removal into River Basin Management Plans.  They should include:

  • Development of an action plan to prioritise removal of dams that are obsolete or have insignificant benefits to society, and integration of this plan within the 3rd River Basin Management Plans;
  • Redirection of finances to make funds available for barrier removal in the 3rd River Basin Management Plans;
  • Delivery of status reports on the progress of dam and barrier removal, including presenting the positive benefits of removals

More information on dam removal here.


The use of water for hydropower is one of the biggest impacts on ecology and continuity of river systems and has caused the loss of valuable fish stocks in many Nordic rivers. It is also one of the key solutions supported by the renewable energy directive, which in many cases may compromise the achievement of WFD objectives if the two directives are not implemented in a mutually balanced manner. In the renewable energy directive, there is comprehensive sustainability criteria for biofuels but not for hydropower. This situation can lead to competing objectives in safeguarding or re-establishing connectivity of rivers.

Across Europe there are existing and now redundant hydropower dams, existing plants that require renewal or renegotiation of licenses and newly planned hydropower development, especially in Central and Eastern Europe. Each scenario requires evaluating differently but there needs to be coherence between the renewable energy and WFD legislation.

From the side of the energy sector, hydropower is considered important because of the ability to generate according to energy usage, to balance the production by other sources. The majority of hydropower is produced by big hydropower stations which are designed to be regulated in this way. Conversely, small or pico ‘run-of-river’ hydropower contributes only a minor percentage to the total generation of renewable energy and cannot provide this energy regulation facility. However, they can have a big cumulative impact on river continuity and river ecology.

In some countries there has had to be significant progress to implement strict guidelines and permitting for low head micro/pico hydro, due to the increased demand from rapidly introduced government incentive schemes. In some countries like Finland and Sweden there are examples from municipalities and municipal power companies choosing to stop their existing small hydropower because of other more important uses like recreational fishing. There are now examples also of projects to demolish big hydropower plants and dams, to revive migratory fish stocks. The biggest ongoing dam and power plant removal project in Europe is on the Sèlune River in France.

New hydropower projects that compromise the achievement of WFD objectives should not be subsidised. New permits should comply with the requirements of the WFD article 4.7, including up-to date mitigation measures for all new permits. At existing power plants, permit renewal applications or license revision should always assess the possibility to improve fish passage provision and also restoration and construction of habitats for ensuring natural life cycles, including the necessary environmental flows.

There are promising results in terms of restoring natural reproduction in old or constructed channels with the introduction of ecological flows, but this is still not yet a common measure across Europe. In the national fish pass strategy of Finland new habitats in bypass channels are seen as an important tool. River sections which have been left dry because of water abstraction into power plants have be restored by agreeing sufficient ecological flows.

To better manage the interaction between sustainable hydropower energy and good river ecosystems, national level change of legislation will be needed in many countries.

In 2020 in Sweden, a new law enters into force that compels all water power plants to apply for re-examination to ensure compliance with modern environmental requirements and EU directives.

In Norway, there are positive examples of the development of new tools and mitigation measures that allow for continued hydropower production in combination with significantly reduced environmental impacts, like the "manual for environmental design in regulated salmon rivers[2]". The national plan for revision of over 100 prioritized hydropower licenses, in combination with introduction and increased use of "nature management clauses" in licenses in Norway, aim to reduce the negative environmental impact through modernized environmental requirements, for instance introduction of ecological flows, improved fish passage and restoration of salmon spawning grounds and river mussel habitats.

ECRR’s view is that there should be clear cross-cutting guidance for hydropower at the EU level. This guidance should include:

  • not subsidizing projects that compromise the achievement of WFD objectives,
  • to require strict mitigation measures in the permitting policy of member and aspirant countries,
  • implement revision of licenses for existing facilities to bring them in line with WFD requirements,
  • and to assess the possible removal of hydropower dams that are obsolete or have insignificant benefits to society.

AMBER Project

AMBER stands for Adaptive Management of Barriers in European Rivers and seeks to apply the management to the operation of barriers in European Rivers to achieve a more effective restoration of stream connectivity. To do this, they develop tools, models and toolkits that will allow hydropower companies and river managers to maximize benefits and minimize ecological impacts. An important part of the AMBER project is to create an inventory of barriers within Europe rivers – so called barrier ATLAS. With this atlas the AMBER Team and environment managers can make strategic and and educated management plans enhancing the health of European rivers.More information on the Amber Project here. 


[1] Belletti, B., Rinaldi, M., Buijse, A.D., Gurnell, A.M., Mosselman, E (2014) A review of assessment methods for river hydromorphology. Environmental Earth Sciences.

[2] https://www.researchgate.net/publication/309075303_Handbook_for_environmental_design_in_regulated_salmon_rivers

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