The first stages of the restoration of the spit between the river Bure and Salhouse Broad to 1946 specifications.

For the last sixty years the marginal zone at Salhouse Broad has slowly eroded. In the current situation the spit has become significantly narrow, further erosion would threaten the structural integrity of the river bank and related riverside mooring. The PRISMA project aims to restore the 1946 waterline, by re-establishing reedbed. The 7,000m2 of reedbed shall be constructed by placing a retaining structure at the 1946 waterline and backfilling the void with sediment. The focus of the construction practises is on sustainability and innovation. Locally sourced alder poles shall be used for the piling. A retaining wall is to be constructed made of a woven geo-textile bag ‘Geotube©’. The four geo-textile bags have a total length of 170 metres, a width of 8.5 metres, a circumference of 18.6 metres and will hold approximately 3,000m3 of sediment. The sizable geotube© relies on gravity unlike conventional retaining structures. Sediment used for the restoration project shall be dredged locally from the navigation channel of the river Bure. Dredging will be carried out with a conventional crane and grab. The sediment requires to be transported to the Broad by barge where it shall be unloaded by excavator and backhoe. The excavator will place the sediment into a screener and subsequently a concrete pump. This pump is capable of pumping with relatively solid sediment through pipelines into the geotube© and backfill.

The final product will be a natural reedbed in the broad with a strengthened river bank, made possible with reused sediment; no geo-textiles shall be visible.

 

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