Rehabilitation of banks and riparian zone

Description of measure

This measure refers to rehabilitation of degraded bankside habitats to improve their physical structure and the condition of the riparian zone.  Bank rehabilitation includes bank reprofiling, the creation of aquatic ledges and removal of hard bank protection.  This measure may be undertaken in combination with Managing bank instability and erosion where these have been identified as a problem.

Application

This measure may be applied to rivers where bankside habitats have previously been degraded as a result of channel modification or bank protection.  For example, resectioning (modification of the channel cross section, usually through widening and deepening) can result in unnaturally steep banks with little habitat diversity.  It is important to determine whether there is an underlying bank erosion or instability problem and address the cause of the problem and mitigate the effects. Rehabilitation should only be undertaken once an assessment of the reach within the wider river network has been undertaken to ensure that measures put in place are appropriate. Rehabilitation of the riparian zone for example through planting of vegetation will not be effective if an underlying bank erosion or instability problem has not been addressed.

Rehabilitation may begin with the removal of hard bank protection which may be applied wherever it is determined that the protection is obsolete or can be replaced by soft engineering solutions. It is important to consider an alternative solution that avoids the need for bank protection and allow natural adjustment, for example by relocating footpaths away from the river to provide space for natural bank adjustment to occur.

Use of bank rehabilitation measures may be constrained in high energy environments where it is determined that hard bank protection is necessary to protect development.  This measure will be most effective if it is targeted in individual reaches, although it may also help to improve longer sections of the river. 

Benefits for Water Framework Directive

Bank rehabilitation aims to reduce the uniformity of the existing bank profile and re-establish a more natural hydrological gradient suitable for colonisation by a range of species.  Reprofiling of the channel banks may also help to create flow diversity within the channel if implemented alternately along the river.  This may help to increase localised flow velocities and reduce fine sedimentation on the channel bed.  This measure can help deliver objectives of the Water Framework Directive, by:

  • Assisting the recovery of natural channel form and re-establishment of bank adjustment processes. This can have benefits at the site by aiding re-establishment of varied bank profile and flow velocities.
  • Re-establishing shallower marginal habitat and a hydrological gradient which is likely to benefit macrophytes, invertebrates and fish. Removal of hard bank protection will also enable re-establishment of vegetation on the bank face and bank top, which provides shelter and shading along the channel.
  • Avoiding knock-on impacts on bank stability further upstream and downstream due to discontinuity in bank characteristics and disturbance of natural bank adjustment processes. This can help avoid instability that may be associated with the presence of bank protection by enabling natural lateral adjustment.
  • Improvement in water quality as a result of more varied low flow conditions.

There are several wider benefits that may be associated with bank rehabilitation, including:

  • Increased biodiversity along the river corridor benefiting mammals, such as otters and water voles, and insects.
  • Creation of additional channel capacity during high flows through the incorporation of embayments into the design of bank reprofiling works.
  • Improvement in the aesthetic appearance of the channel, which may be of particular benefit in an urban environment.
  • Potential to incorporate public access and amenity features as part of the works – e.g. provision of viewing platforms.

In addition, bank rehabilitation can be reasonably cheap to implement and is a measure that could potentially be undertaken by local interest groups with appropriate guidance.

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

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