Case study:River Dulais Restoration Project

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Location: 51° 54' 12", -3° 58' 13"
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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 Richard
Main contact surname Edwards
Main contact user ID
Contact organisation Salix River & Wetland Services Limited
Contact organisation web site
Partner organisations Natural Resources Wales
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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Image gallery


Root wad being installed in the bank
Dulais before restoration (2003)
Dulais after restoration (2005)
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Catchment and subcatchment

Catchment

River basin district Western Wales
River basin Loughor to Taf

Subcatchment

River name Dulais - conf with Ddu to confluence with Tywi
Area category 10 - 100 km²
Area (km2)
Maximum altitude category 200 - 500 m
Maximum altitude (m) 285
285 m
0.285 km
28,500 cm
Dominant geology Siliceous
Ecoregion Great Britain
Dominant land cover Improved grassland
Waterbody ID GB110060036210



Site

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

Reach length directly affected (m) 500 m
0.5 km
50,000 cm
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 €
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 33
33 k€
33,000 €
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

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

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


Monitoring

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

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

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
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.