Healthy waterways are at the heart of economic and social well being and good maintenance is vital. But waterways are increasingly faced with complex environmental issues. PRISMA aimed to meet these challenges by developing better methods to process, treat and re-use dredged sediment, with a greater focus on sustainability.
We were awarded more than £700,000 from the European Regional Development Fund to work with partners in the Netherlands, Belgium and France, sharing knowledge and comparing techniques. As a result the Broads Authority has won awards for some of its work.
The project's main aims were to:
- Develop and test adapted methods to improve the dredging process
- Develop and test innovative methods for the treatment of dredged sediment
- Improve the re-use of dredged sediment and promote re-use.
The key results were:
- The re-use of 67,600 cubic metres of sediment for habitat creation, floodbank strengthening, agricultural land and the restoration of eroded spits, banks and reedbeds
- Investments in equipment, machinery and facilities which will help our work beyond the project end, including a new dockyard at Thorpe and a new mud wherry
- Invaluable knowledge gained about different methods of dredging, sediment treatment and re-use through pilots, trials and cross border working
- Various retaining structures, dredging equipment and transport techniques were all trialled, including submersible and concrete pumps, a geotunnel and a centrifuge dewatering system.
You can find out more about the results of the project in the PRISMA summary paper.
A number of pilots were carried out under PRISMA which not only resulted in ongoing tangible benefits but contributed to knowledge and understanding about different sediment management methods to help inform our work in the future.
Reedbeds that had been lost to erosion over a number of decades were restored using dredged sediment. Fabric-lined steel mesh baskets created the perimeter of a spit of land and the void was filled with sediment and planted with reed seed. Read more about Duck Broad.
At Salhouse Broad giant geotextile bags were filled with sediment and the void infilled in the same way. This innovative technique won the UK's first Working with Nature Certificate of Recognition, one of only three to be awarded in Europe, and a commendation in the 2013 Waterways Renaissance Awards.
Upton Little Broad
Upton Little Broad was an extremely shallow lake with little aquatic life. Dredging increased the depth to improve water clarity and encourage plants. The dredged sediment was pumped into geotextile bags and, once the water had drained out, was spread on agricultural land to improve the soil. Using geotextile bags removed the need for major earthworks.
Sediment was used to recreate reedbeds on a section of the Lower Bure where the riverbank had been set back by the Environment Agency. The reedbeds create a natural buffer to better protect the banks from erosion at high tide.
Thorpe River Green
An excavator on a pontoon was used to dredge the River Yare at Thorpe River Green. The pontoon was particularly suitable for small scale dredging work because of its manoeuvrability. The sediment was taken to Postwick tip, a licensed landfill site, because of the raised concentrations of mercury in this stretch of river.