Sediment has frequently been viewed as a problem, and has been dredged or removed to maintain clear flowing waters. This can encourage further erosion, enlarging watercourses, changing the way they convey water, altering or destroying habitats and leaving artificial defences vulnerable.

Developing a sediment management strategy aims to ensure that sediment is managed in a strategic way to minimise its impacts on water bodies and the habitats that they support. The activity should work with natural processes to ensure that sediment is sustainably managed from source to sea.

Techniques

A variety of techniques can be used to undertake this activity, including:

• Develop of a sediment management strategy - This should include all water bodies in a river catchment or coastal cell to ensure that catchment-scale processes are addressed
• Change the way land drains are managed - This can reduce sediment input
• Reinstate sediment that has been removed - Introduce sediment as part of habitat enhancement works or to improve morphology / sediment transport elsewhere in the water body
• Target sediment removal - So that flood risk is reduced using sediment traps and only undertaking localised dredging
• Allow natural recovery - By minimising the frequency of maintenance

Benefits

The appropriate management of sediment can achieve a range of benefits:

• Direct ecosystem benefits associated with the maintenance of biodiversity
• Natural erosion protection (e.g. through the retention of sediment in front of vulnerable areas)
• Improved water quality through the reduction of suspended sediments
• Reduced costs of maintenance (dredging)

Case Study Benefits

This diagram displays a comparison of benefits scores (using a high-level ecosystem service assessment methodology) associated with the techniques used in each case study. More details on the methodology can be found here. 

These case studies are examples of how this environmental improvement could be delivered. Some are delivered through FCERM (EA) funding and some by other stakeholders (local councils, IDBs, developers, etc.)

• Whitfield Moor (Peatscapes Project) Grip Blocking
• River Hull Headwaters WFD Wet Woodland Project (sediment)

Cost bandings are as follows:

• £ = £1k-£10k
• ££ = £10k-£50k
• £££ = £50k-£100k
• ££££ = £100k-£500k
• £££££ = £500k+

An explanation of the headings in the case studies and the ecosystem services compass diagrams can be found: HERE

Other relevant case studies:

• River Hull Headwaters SSSI Wet Woodland Projec (natural obstructions)
• Buxted Park Weir, Middle Ouse Restoration of Physical Habitats

• Environment Agency (2013) Evidence: Impacts of Dredging
• Environment Agency (2011) River Sediments and Habitats
• Environment Agency (2010) Dredging Pilot Studies Report
• Environment Agency (2012) Rural Sustainable Drainage Systems
• Environment Agency (2010) Fluvial Design Guide

Throughout this best practice, 'environmental improvements' refer to WFD 'mitigation measures'. The names of some mitigation measures are different in England, Scotland and Northern Ireland.

This mitigation measure is named: 

• Sediment management strategies (develop and revise) which could include a) substrate reinstatement, b) sediment traps, c) allow natural recovery minimising maintenance, d) riffle construction, e) reduce all bar necessary management in flood risk areas (England)
• Manage sediment at an impoundment (e.g. getting it past the impoundment) (Scotland)
• Manage sediment sensitively (e.g. where it was previously extracted) (Scotland)
• Investigate the source of excessive silt and eliminate the cause (NI)
• Ensure the natural channel form is considered in any restoration works (NI)
• Cease abstraction and dredging if possible (NI)

• Healthy Catchments - managing water for flood risk and the Water Framework Directive

• Environmental improvements & case studies

• What is the WFD?

• Glossary