Dredging in the Broads begins lost island restoration
The Broads Authority is trialling an innovative project to use gabion baskets lined with geo-textile materials for the disposal of dredgings from the navigation channel. The interlocking baskets will form a perimeter into which dredged sediment will be placed to form an island.
The experimental work to create a 20m x 20m island will be monitored for a year to assess its viability, stability and habitat creation qualities. If the trial stage is successful and Natural England, Norfolk Wildlife Trust and the Environment Agency agree, the whole island measuring about 1 hectare (2.3 acres) will be restored. This will help separate Duck Broad from the main channel and give shelter to over wintering birds while re-creating reed swamp habitat and restoring channel depth for navigation.
Over £10,000 has been invested in measures to reduce the risk of an outbreak of Prymnesium algae which can prove toxic to fish if the algae blooms. These costs include an impermeable silt curtain which will surround the dredger to limit the release of nutrients and sediment into the main waterway, and monitoring equipment.
Water quality is being tested in three locations on a daily and weekly basis for Prymnesium levels, salinity, dissolved oxygen, temperature and turbidity. An emergency action plan in the event of a Prymnesium outbreak has been drawn up between the Broads Authority and Environment Agency.
Rob Rogers, Broads Authority Head of Construction and Facilities, who is managing the work, said: “The project team has worked very closely with Natural England, the Environment Agency and angling groups to address concerns over Prymnesium and aesthetic issues raised during the consultation stages. The water sampling is showing very low levels of Prymnesium and favourable conditions for dredging. The sampling will continue for some weeks after the project to ensure good scientific data is gathered.”
Heigham Sound, which leads to Hickling Broad and Horsey Mere, has silted up to a depth of 90cms in places resulting in some traditional Broads sailing cruisers going aground. Dredging has been delayed because a disposal site could not be found.
The Broads Authority has designed and built the cages based on gabions filled with soil and rock which have been used by the British Army as barricades in Afghanistan. If this pilot scheme is successful it could be rolled out to restore other eroded islands across the Broads. The work, centred on Duck Broad, does not obstruct boating.
18/05/10
