Sediment Management
Dredging
Dredging on the River Bure
The Broads Authority, as navigation authority, has adopted a river catchment approach to sediment management. Our aim is to provide a means of ensuring the sustainable long-term management of sediment within the Broads. The location, volume and movement of sediment, from its sources to where it is deposited, is key information required for successful management. This type of approach is needed within the Broads to protect both the inland navigation and the internationally important wetland.
Our objectives for managing sediment are to:
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Identify the volume of sediment entering the Broads
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Reduce sediment coming into to the waterways through working closely with other organisations
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Clearly define the desired channel dimensions within the waterways, which will inform the future dredging requirement
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Maximise beneficial reuse of dredged sediment
Maintaining adequate water depths for navigation is an important river management task for the Broads Authority. There are two main dredging methods routinely used: grab (or excavator) and suction. Suction dredging works by having a floating platform with an engine that powers a suction pump. The bottom sediment, with a high water content, is passed along tubes to an adjacent disposal site, often a field of low ecological quality.
Dredging is carried out by the Authority throughout the year, along with other river maintenance works.
In early 2006 the Authority trialled a novel technique called water injection dredging. This works by injecting water into the sediments from a specially equiped boat. As water is pumped into the sediment it becomes mixed into the water. The muddy mixture is then carried away on the outgoing tide, flushing the fine sediment downstream and ultimately out to sea. As this method requires strong tidal flow to remove the sediments, it could only possibly be used in the lower reaches of the Broads rivers and in areas not contaminated by toxic substances.
Over the last 60 years, rates of sedimentation have accelerated as a consequence of the environmental changes in the Broads, particularly from greater numbers of algae in the lakes and increased soil erosion. We hope that improvements in water quality, preventative measures taken to reduce the causes of bank erosion and improved methods of bank protection will ultimately lessen the need for dredging.
The Broads Authority’s dredging plans for this year identifying the priority areas for works are set out in the Action Plan 2009/10, and this also sets out progress achieved on projects carried out in previous years.
To find out more see our Sediment Management Strategy and Sediment Management Strategy Action Plan
