Gravel reinstatement in rivers

Description of measure

The measure includes methods of mitigating the impacts of historic sediment removal through reinstatement of gravel substrate within the channel, incorporating both gravel augmentation (or seeding) and direct modification of the channel bed to create substrate features (e.g. riffles).

Application

This measure is relevant to all rivers, including both gravel bedded rivers and those with mixed bed substrates.  Sediment reinstatement may be applied in rivers that where sediment removal has previously taken place and natural recovery of sediment substrate conditions is not likely due to a lack of sediment supply or degree of historical modification.  In addition, reinstatement could also be applied in rivers where impounding structures (e.g. large weirs, dams and reservoirs) prevent the downstream transport of coarse sediments. 

Reinstatement should be undertaken in a sensitive manner, and due consideration given to the appropriate form of the reinstated bed sediments.  For example, the creation of gravel riffle features within a river system should only be applied where pool-riffle sequences would naturally occur, and may not be appropriate for low energy streams (Environment Agency, 2008).

Where sediment has previously been removed from a river system, local reinstatement of in-channel sediment-related features only enhances localised habitat rather than restoring deficient natural processes associated with sediment supply.  Sediment features are often designed to be static rather than transitory as they may naturally be.  Only by restoring the sediment regime at a sub-catchment or catchment-scale can reinstatement be successful at larger spatial and temporal scales. 

Benefits for Water Framework Directive

Gravel reinstatement in rivers can help deliver objectives of the Water Framework Directive by:

  • Allowing the development of sediment-related features which occur naturally in alluvial channels.  The presence of such features is important in providing a range of flow velocities, flow depths and substrates and hence a diversity of habitats within a channel.  Selection of substrate of a suitable grain size distribution is therefore important to ensure that it is suitable for the types of communities that are present in the river. 
  • Assisting the recovery of more natural channel morphology and provide more diverse bed conditions and habitats upon which macrophytes, invertebrates and fish depend.
  • Improving water quality status, for example, through the oxygenation of water over riffles and the reducing the re-suspension of fine sediment that can cause turbidity and spread of sediment-bound contaminants downstream.

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

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