Case study:River Dulais Restoration Project

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Location: 51° 54' 11.98" N, 3° 58' 13.08" W

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Project overview

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Status	Complete
Project web site
Themes	Fisheries, Habitat and biodiversity
Country	Wales
Main contact forename	Nick
Main contact surname	Elbourne
Main contact user ID
Contact organisation	River Restoration Centre
Contact organisation web site	http://www.therrc.co.uk
Partner organisations	Environment Agency Wales, Salix River & Wetland Services Limited
Parent multi-site project
This is a parent project encompassing the following projects	No

River Dulais one year after restoration works completed. Courtesy of RRC

Project summary

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The River Dulais (Afon Dulais) is a tributary of the River Towy, and is an important spawning habitat for migratory fish. The river had a history of instability and planform adjustment. Unrestricted grazing, by sheep and cattle, had resulted in a loss of bankside vegetation. 4.9 km of the catchment had been fenced, however some areas needed more extensive bank protection. Root wads were installed into the bank as an alternative to blockstone. In areas where the channel had additional capacity to scour or degrade brushwood protection was also used in between root wads. Careful thought was given to creating a smooth profile along the bank to reduce the risk of erosion. The riverbank above each root wad was protected by erosion control matting. Forty root wads were installed over eighty metres of bank, with two to three metres of trunk left attached to the root wad. Crack willow (Salix fragilis), grey willow (Salix cinerea) and white willow (Salix alba) with an average trunk diameter of between 30cm and 60cm were used. Live willow was chosen as each tree should root and shoot to quickly bind the surrounding bank. All trees were sourced from within the Dulais catchment and two adjacent river valleys. Since installation stabilisation of a complex outer meander bend has been achieved and each of the root wads installed has grown well.

Monitoring surveys and results

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Lessons learnt

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Catchment and subcatchment

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(affects all case studies in this subcatchment)

Site

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Name	River Dulais
WFD water body codes	GB110060036210
WFD (national) typology
WFD water body name	Dulais - conf with Ddu to confluence with Tywi
Pre-project morphology
Reference morphology
Desired post project morphology
Heavily modified water body	No
National/international site designation
Local/regional site designations
Protected species present	No
Invasive species present	No
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	0.01 - 0.1
Average channel gradient
Average unit stream power (W/m2)

Project background

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Reach length directly affected (m)	500 m0.5 km <br />50,000 cm <br />
Project started	2004/05/01
Works started
Works completed
Project completed	2004/05/31
Total cost category	10 - 50 k€
Total cost (k€)	33 k€33,000 € <br />
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		3333 k€ <br />33,000 € <br />	Salix
Post-project management and maintenance
Monitoring

Supplementary funding information

Works split into €20k for revetment work and €13k for fencing

Reasons for river restoration

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Mitigation of a pressure
Hydromorphology	Channel pattern/planform, Structure & condition of riparian/lake shore zones
Biology	Lack of vegetation, Macrophytes
Physico-chemical
Other reasons for the project	Promote soft-engineering/river restoration techniques

Measures

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Structural measures
Bank/bed modifications	Bank stabilisation
Floodplain / River corridor	Control of riparian vegetation, Creation of wetlands
Planform / Channel pattern	Channel narrowing
Other
Non-structural measures
Management interventions	Fencing
Social measures (incl. engagement)
Other

Monitoring

Hydromorphological quality elements

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quality elements

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

Biological quality elements

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quality elements

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

Physico-chemical quality elements

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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

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

Monitoring documents

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Image gallery

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Root wad being installed in the bank

Dulais before restoration (2003)

Dulais after restoration (2005)

Additional documents and videos

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Additional links and references

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Link	Description
http://www.therrc.co.uk/case studies/rrn%20issue%2023.pdf	River Restoration Centre news article

Supplementary Information

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Monitoring encompassed HABSCORE and electro fishing surveys, which were undertaken by the Environment Agency Wales just after construction in 2004 and again in 2006. Three sites were surveyed within the project reach, and a further three upstream to act as controls. At each site two semi-quantitative and one quantitative electro fishing surveys were carried out to determine population estimates for salmon and trout fry and parr. No marked differences were observed in fish densities between the two survey occasions, with some sites showing a reduction in fish numbers. However, it should be noted that the post-scheme surveys were undertaken just one year after the works, with the full benefits not likely to be realised until several years after implementation.

Where flow is focussed directly at the root wads, an area of localised scour has formed under the base of the exposed root ball. This provides an overhanging vegetated bank, which is a valuable new habitat feature. Diverse bankside cover has resulted and cleaner gravels are present, with visibly less fine sediment. Overall the channel geometry is now similar to more well-vegetated reaches of the river. Due to its rural and over-wide location maintenance of flow conveyance was not deemed to be an issue, even with the very fast growth rate of willow no post-project maintenance (coppicing) was required.