The final stage of the innovative reed bed creation at Duck Broad has begun with the dredging of Heigham Sound which will increase water depth for boat users.
Contractors Goodchild Marine Services are pumping 10,000 m³ of sediment from the navigation channel into a void created by 250 mud-filled gabion baskets. Once the spit of mud has dried out it will be planted with young reed to restore habitat and provide a quiet area for wildlife in Duck Broad as it was 60 years ago.
Dredging is being carried out using a mud pumping method, which minimises disturbance to sediment. A silt curtain has been placed round the perimeter of the new spit, to prevent the spread of any suspended sediment during the filling process. Dredging in cold water conditions over the winter also reduces the risk of working when natural populations of the algae Prymnesium are most likely to bloom, which is important for this project, as the algae can be toxic to fish.
Weekly water monitoring will check that Prymnesium numbers remain within the threshold set by Natural England and sensors will record water quality data every half hour based on research carried out by the John Innes Centre.
Dr Dan Hoare, the Broads Authority’s Environment and Design Supervisor, said: “We have put lots of safeguards in place to prevent any environmental impacts of the mud pumping and inconvenience to boating. The increased water depth will be of great benefit to all users of these waterways. It should also help improve water quality in the longer term as sediment on the bottom will be stirred up less.”
The work is being match-funded by the European Regional Development Fund through PRISMA (Promoting Integrated Sediment Management) which involves working with Dutch, Belgian and French partners to develop new ways of reducing and re-using sediment.
Press Release, November 26, 2013