Case study:Ddu Restoration Project

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Location: 52° 57' 36.89" N, 4° 8' 28.76" W

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Project overview

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Status	In progress
Project web site
Themes	Fisheries, Habitat and biodiversity, Hydromorphology, Land use management - agriculture, Monitoring
Country	Wales
Main contact forename	Huw
Main contact surname	Jones
Main contact user ID	User:Huw Jones
Contact organisation	Natural Resources Wales
Contact organisation web site	http://naturalresources.wales/
Partner organisations	Snowdonia National Park Authority, Welsh Government
Parent multi-site project
This is a parent project encompassing the following projects	No

Restoration of the river

Project summary

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This river was badly damaged by dredging / drainage operations in 1995-6. Investigation work led to the discovery of a previously unknown population of Margaritifera margaritifera - the population was badly damaged by this work. Work to restore some sections of the Afon Ddu has been carried out by legacy Environment Agency Wales and Countryside Council for Wales and partner organisation Snowdonia National Park Authority since 2005. The bulk of this work concentrated on fencing out the river to reduce livestock access, but a short section of the most damaged section was restored in 2006. The river was designated as a pearl mussel Site of Special Scientific Interest in 2010/11. Since the formation of Natural Resources Wales, further work has been carried out with the aim of restoring in channel geomorphology, through the replacement of boulders and gravel seeding with an objective of improving the habitat for salmonids and Margaritifera margaritifera. The small catchment size means that close co-operation with landowners is likely to be more effective than in larger, dispersed, catchments in terms of achieving water quality objectives. Approx. £90,000 has been spent on fencing and habitat works on this river since 2005 by the partner organisations. This river is an UK Biodiversity Plan Priority River for Margaritifera margaritifera, along with two other Welsh rivers.

Monitoring surveys and results

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Long term monitoring of Margaritifera margaritifera numbers in this river indicate a continuing decline in adult numbers, in common with other Welsh rivers. In the Afon Ddu, this has been mostly linked to unsuitable river habitat, both due to physical modifications and some issues with water quality. Monitoring of the success of the restoration work will in future be linked to NRWs use of the Redox potential measuring technique to determine the quality and cleanliness of the interstitial gravel which the juvenile stage of Margaritifera margaritifera rely upon. Monitoring indicates that the encystment stage of the Margaritifera margaritifera is occurring normally in this river, and that juvenile salmonid host numbers are good.

Lessons learnt

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Landowner buy in and suitable catchment management is essential, and there is a good uptake of the Welsh Government's Glasdir Agri-Environment scheme in this small catchment. Successful captive rearing of juvenile mussels at the NRW Aquaculture Unit at Cynrig is considered to be an important future development to secure the future of the species. Due to the sensitive species present in this river, a spread out one step at a time approach to restoration has been appropriate.

Image gallery

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Catchment and subcatchment Select a catchment/subcatchment Site Edit site Name Afon & Llyn Du WFD water body codes GB110065053690 WFD (national) typology WFD water body name Cwmystradllyn Pre-project morphology Over deepened Reference morphology Pool-riffle Desired post project morphology Pool-riffle Heavily modified water body No National/international site designation UK - Site of Special Scientific Interest Local/regional site designations Protected species present Yes Invasive species present No Species of interest Freshwater pearl mussel (Margaritifera margaritifera) Dominant hydrology Perennial Dominant substrate Gravel River corridor land use Non-intensive agriculture (grazing) Average bankfull channel width category Less than 2 m Average bankfull channel width (m) Average bankfull channel depth category Less than 0.5 m Average bankfull channel depth (m) Mean discharge category Less than 0.1 m³/s Mean annual discharge (m3/s) Average channel gradient category Average channel gradient Average unit stream power (W/m2) Project background Edit project background Reach length directly affected (m) Project started 2005/06/01 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 Monitoring Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Hydromorphology Biology Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Boulder restoration, Addition of substrate and in channel features Floodplain / River corridor Fencing of riparian zone Planform / Channel pattern Creation of fish passes Other Deculverting Non-structural measures Management interventions Agricultural business changed its way of working Social measures (incl. engagement) Other Monitoring Hydromorphological quality elements Edit Hydromorphological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Biological quality elements Edit biological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Physico-chemical quality elements Edit Physico-chemical quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Any other monitoring, e.g. social, economic Edit Other responses Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Monitoring documents Upload monitoring documents Additional documents and videos Upload additional documents Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information