Create and restore backwater habitats

Description of measure

Backwaters are defined as areas of water that are open to the channel at one end (usually the downstream end if it is a cutoff meander or oxbow). They are aquatic habitats that are connected to the main channel, sometimes seasonally or periodically, characterised by slow currents, shallow water and silt substrates. Backwaters can be formed naturally as the main river migrates across the floodplain, cutting off meanders. The emphasis of this design guidance is on restoration or creation of self-sustaining backwater habitats.

Application

Backwater habitats can be used as habitat restoration after rivers have been straightened and resectioned to increase morphological diversity. There is often an opportunity to include a range of backwater habitat types into flood risk management or river restoration projects. Different types of backwater habitat can be created depending upon the situation including:

  • Restoring or enhancing existing features where these exist such as cut-off meanders, oxbows or flood swales.
  • Creating new off-line spawning and rearing habitat adjacent to the main channel where there are no remnants of backwater (usually in areas where the floodplain has been developed).
  • Retaining sections of redundant watercourse as part of a larger river restoration project where a restored river is constructed on a new alignment. At the downstream end of meander sections it is possible to connect the redundant sections retain a section of backwater.

Benefits for Water Framework Directive

Backwaters provide important habitat for a range of aquatic flora and fauna, including invertebrates, macrophytes and fish. They can help deliver objectives of the WFD by:

  • Providing refuge for juvenile fish during times of flood (Saldi-Caromile et al., 2004).
  • Creating warmer conditions and shallow refugia in times of flood which are ideal nursery areas for young amphibians, invertebrates (e.g. dragonflies and damselflies) and other insects which live in still, unpolluted waters.
  • Increasing morphological diversity and enhancing the ecological value of the river channel.
  • Promoting the removal of fine silt from river systems. Reduction in suspended sediments promotes better water clarity, allowing light to penetrate to greater depths, benefiting macrophytes and phytobenthos along with the invertebrates that depend on them.

To read more about the effectiveness of the measure within academic literature please click here: Effectiveness for Biological Quality Elements

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