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

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Revision as of 10:33, 4 October 2016

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Location: 57° 2' 53", -2° 30' 22"
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Project overview

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Status In progress
Project web site http://https://www.pearlsinperil.org.uk/
Themes Fisheries, Habitat and biodiversity, Hydromorphology, Water quality
Country Scotland
Main contact forename Jackie
Main contact surname Webley
Main contact user ID User:Pearlsinperil
Contact organisation Scottish Natural Heritage
Contact organisation web site http://http://www.snh.gov.uk/protecting-scotlands-nature/protected-species/life-projects/pearls-in-peril/
Partner organisations Dee District Salmon Fishery Board, Dee Catchment Partnership, Cairngorms National Park, Forestry Commission Scotland, Scottish Environment Protection Agency (SEPA)
Parent multi-site project

Case_study:Pearls in Peril LIFE project

This is a parent project
encompassing the following
Pearls in Peril project logo

Project summary

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‘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

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

Lessons learnt

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During the procurement process for the physical in stream works, it would have been beneficial to provide contractors with templates of the information required to allow them to meet the mandatory requirements more easily.

Image gallery

75106 PIP Dee Upper 29 June 2016.jpg
75106 PIP Dee Middle 29 June 2016.jpg
Upper Dee Tree Enclosures.jpg
Dee Surveying 0.jpg
Dee Croy-removal.jpg

Catchment and subcatchment


WFD water body codes
WFD (national) typology
WFD water body name
Pre-project morphology
Reference morphology
Desired post project morphology
Heavily modified water body
National/international site designation
Local/regional site designations
Protected species present
Invasive species present
Species of interest
Dominant hydrology
Dominant substrate
River corridor land use
Average bankfull channel width category
Average bankfull channel width (m)
Average bankfull channel depth category
Average bankfull channel depth (m)
Mean discharge category
Mean annual discharge (m3/s)
Average channel gradient category
Average channel gradient
Average unit stream power (W/m2)

Project background

Reach length directly affected (m)
Project started 2012/09/03
Works started
Works completed
Project completed
Total cost category
Total cost (k€)
Benefit to cost ratio
Funding sources

Cost for project phases

Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname
Investigation and design
Stakeholder engagement and communication
Works and works supervision
Post-project management and maintenance

Reasons for river restoration

Mitigation of a pressure To safeguard the future of the most important pearl mussel populations in Great Britain
Biology FWPM and salmonid abundance
Physico-chemical water quality
Other reasons for the project


Structural measures
Bank/bed modifications
Floodplain / River corridor
Planform / Channel pattern
Non-structural measures
Management interventions
Social measures (incl. engagement)


Hydromorphological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Biological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative
Invertebrates: Abundance Yes Yes No Yes No
Fish: Abundance Yes Yes No Yes No

Physico-chemical quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative
Oxygen balance No No Yes No No

Any other monitoring, e.g. social, economic

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Monitoring documents

Additional documents and videos

Additional links and references

Link Description

Supplementary Information

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