Difference between revisions of "Case study:Pearls in Peril LIFE+ GB Project - River Dee"

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Project summary

‘Pearls in Peril’ is a UK-wide project to safeguard the future of the freshwater pearl mussel. The River Dee is designated as a Special Area of Conservation with internationally important populations of freshwater pearl mussel and Atlantic salmon. It is presently assessed as being in ‘unfavourable’ condition by Scottish Natural Heritage. The project has identified sections of the River Dee at Banchory, Aboyne, Sluie/Commonty and Braemar (Mar Lodge)where in-stream restoration has been undertaken. With a further site at Slugain, Braemar to be completed in 2016.

The River Dee at Banchory, Aboyne and Sluie/Commonty is characterised by numerous 'croys' (wedge shaped structures extending from the bank into the river channel that are constructed of boulders removed from the river bed). The croys were mostly built during the 1990's and their purpose was to improve conditions for Salmon fishing. However, the croys did not have the desired effects and in addition to damaging the riverbed habitat when they were built, they also resulted in scour and changes to substrate composition. Pearls in Peril has removed a total of 27 croys and re-distributed the boulders back into the river channel.

This work has restored approximately 18,000m2 of river bed habitat. The removal of the croys, in particular the larger paired croys, creates more natural channel hydraulics and sediment transport. Re-placement of the boulders from the croys on the bed has covered approximately 25% of the main sub-reach and will benefit freshwater pearl mussels through stabilising the bed substrate and creating hydraulic refugia. Boulder placement also provides these benefits and improves habitat for juvenile salmon.

The Car Bank, Braemar - In 1984 the embankment was constructed with a range of materials including local spruce trees, railway sleepers, corrugated iron, approx. 30 old cars, large quantities of concrete, rocks and boulders. Corrugated iron facing was used so that ice would be less likely to become pinned up against the embankment. Pearls in Peril has undertaken controlled removal of the waste materials and re-profiled 90m of bank thus re-connecting the River Dee with its flood plain and restoring natural process that will improve habitat for freshwater pearl mussels and salmonids.

Monitoring surveys and results

Monitoring work is on going and being completed by the Dee District Salmon Fishery Board and the James Hutton Institute (fixed point photography)