Good Practice Sediment Management

Sediments are a natural part of aquatic systems which are essential for the hydrological, geomorphological and ecological functioning of those systems. Sediment forms a variety of habitats, which directly and indirectly support a broad range of flora and fauna. Sediment may need to be managed for a number of reasons, including sediment removal or deposition for flood defence purposes; sediment removal and reinstatement for fisheries interest; aggregate extraction; and land drainage.

The aims of sediment management might be to:

  • Ensure environmentally acceptable methods for the disposal of dredged sediments, ensuring use for enhancement where appropriate.
  • Manage sediment supply at source by putting in place agricultural best practice techniques.
  • Reinstate sediment to increase the quantity and / or quality of spawning habitat for targeted species and reducing fine sediment deposition in spawning and / or rearing habitats.
  • Prevent or control the distribution of contaminated sediments.
  • Coordinate; monitor and manage activities which may affect sediment supply, removal and transport at a catchment scale through implementation of a dredging strategy. A dredging strategy will normally seek to safeguard the geomorphology and biological diversity of surface water; preventing unnecessary sediment removal; and ensuring that sediment removal deemed essential (e.g. for navigation, flood risk management, water supply purposes, infrastructure protection etc.) is undertaken in a co-ordinated and sustainable manner, with minimal impact on biological diversity and natural river processes.

The following mitigation measures are included within this manual:

Sediment removal, particularly of gravel substrate, can have significant adverse impacts on the hydromorphology and biology of rivers. Regular removal is not a sustainable practice as deposition of sediment is a natural response of the river to prevailing flow and sediment conditions. This measure provides guidance on ensuring that appropriate approaches are taken to limit the impact of further sediment removal on hydromorphology and biology. The measure also 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).

In most cases it is recommended that sediment is retained in the river channel because it is an intrinsic part of the functioning of the river system, contributes to diverse channel morphology, and provides vital habitats for aquatic organisms. However, in cases where sediment removal is necessary to maintain river function or would be of demonstrable benefit to ecology and geomorphology, and where sediment supply cannot be controlled, it may be possible to actively manage in-channel sediments. This measure is concerned with ensuring that appropriate approaches are taken to limit the impact of further sediment removal on hydromorphology and biology, in situations where sediment removal is deemed necessary.