Other Maintenance dredging of inland waterways and constructing a breakwater and reedbed with dredged sediment.
The Broads Authority is restoring a lost reed bed and eroded strip of land at Salhouse Broad, Norfolk. (A Broad is a shallow manmade lake, conventionally dug for peat) Erosion over the last 60 years has caused the land between Salhouse Broad and the River Bure to become significantly narrow –down to 2 metres in places-- threatening the integrity of the river bank and its riverside mooring. Now 7,000m ² of reed bed is being constructed using dredged sediment retained by four giant geotextile bags. The geotubes© are fixed to locally sourced alder poles; cut from river banks near Salhouse Broad. The geotubes are being filled with 3000m ³ of sediment dredged from the River Bure to provide a 170m retaining bank. The geotubes, which are 8.5 metres wide and have a circumference of 18.6 m are big enough to drive a car through! Once filled, they will sink below the waterline and the void behind the bags will be filled in with 8000m³ of dredged sediment to restore the reed bed as it was in 1946. Dredging of the river Bure is required for navigational purposes, shoals have accumulated on the inside of bends and other slow flowing areas. Dredging to a depth of 2.00 metres below mean low water is required, allowing pleasure cruisers and sailing vessels to navigate the river. Sediment from the river Bure is being carried to Salhouse by barge where it is unloaded into a pump by an excavator. The pump, conventionally used for concrete, fills the bags via a pipeline. The use of a concrete pump is required because the sediment pumped is undiluted, in-situ sediment. Geotubes have been filled with sediment before, however not with in-situ (solid) sediment with a concrete pump under water! The surface of the geotextile bags will be planted with reed seed and rhizomes sourced from vegetation scrapes, carried out as part of reed bed management on an adjacent site this winter to help restore it as a natural reed bed.
A detailed environmental assessment was carried out prior to the works focussing on the specific works area. The Broads are manmade and require specific management to ensure high quality habitats. The aim is to enhance biodiversity by re-creating reedbed, a habitat type that has diminished locally as well as nationally.
Stakeholders; landowner, local site managers, the Environment Agency and Natural England as well as the navigation committee were involved from the start of the project. This was achieved by liaising with them during individual meetings. The project was also flexible enough to make minor changes where required during the whole process as it is highly innovative. This is done on several occasions.
The project followed the steps described, of particular difficulty was to keep 'all' stakeholders pleased. When one works in a dynamic environment like the broads with many different stakeholders somethimes it takes significant efford to please everyone.
The Broads Authority is part of the National Park family and we act as the stewards of Broads. Besides this duty we also require to maintain navigation. By combining the two aspects we can carry out our work more effectively. Win-win situations are essential for operational as well as economic reasons. We aim at the same time to improve the natural environment.
No extra costs compared to conventional approach Sourcing local materials is somethimes not competative in relation to 'on the shelf' products, however because of the win-win situations and the reduction of transport no extra cost were incurred.
Legal requirements prevented (some of) the Working with Nature philosophy being applied Sediment is still regard as a waste in legislation, 'building' with sediment is therefore particulary difficult. Because we used sediment within the same waterbody, no hinder was incurred.
Please contact William Coulet for further information, video's, photo's reports and other information is available.