Case study:River Cole- Life Project

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Location: 51° 37' 53", -1° 39' 46"
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Project overview

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Status Complete
Project web site
Themes Flood risk management, Habitat and biodiversity, Hydromorphology, Monitoring, Social benefits
Country England
Main contact forename Martin
Main contact surname Janes
Main contact user ID User:UlrikaRRC
Contact organisation River Restoration Centre
Contact organisation web site http://www.therrc.co.uk
Partner organisations European Commission (LIFE funding), River Restoration Project (now River Restoration Centre), Environment Agency, National Trust, Countryside Commission, English Nature (now Natural England)
Parent multi-site project

Case_study:River restoration: Benefits for integrated catchment management

This is a parent project
encompassing the following
projects
No
The restored Cole river

Project summary

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The River Cole at Coleshill is a tributary of the Thames and flows through National Trust owned farmland, North East of Swindon on the Oxfordshire and Wiltshire border.

Background: The river has a long history of modifications and already the Domesday Book of 1086 has a record of a mill in Coleshill. On the earliest map from the area, dated 1666, the river appears to have been straightened for milling. The section downstream of the mill has more recently been enlarged to safeguard agricultural production from flooding. Until the late 1700s, the mill was fed by a small artificial channel carrying water from the Cole, but by 1818 the mill leat had been largely extended to take the entire flow of the Cole, and most of the old river course filled in. This type of historical management is typical of many other rural rivers in the United Kingdom.

Restoration: The River Cole was included in a joint initiative between England and Denmark to demonstrate best practice in urban and rural river rehabilitation and encourage river restoration in Europe. The wider aim was to promote further river restoration and demonstrate how river restoration could provide multiple benefits such as enhancement in wildlife, landscape, recreation, water quality, fisheries, amenities and other local interests.

The restoration of the River Cole was initiated in July 1995. The site consists of a 2.5 km long reach divided into two parts, upstream and downstream of the mill. Upstream of the mill the river was restored to its original course (retaining a small flow in the mill leat) to join the old surviving mill by-pass channel. This new smaller channel encourages beneficial flood storage on the fields and allows fish to pass the mill weir. Downstream the river was reduced in size and remeandered across the old course to a more natural profile, retaining existing mature riverside trees. The restoration of bed level, water level and flood regime was achieved by cutting the new meandering river at a much higher level, similar to that prior to the last major deepening scheme of the 1970s.

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Monitoring surveys and results

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Pre-monitoring:

Ecology

• Macrophytes - number of species found per 500 meter channel length. • Macro-invertebrates - species richness and abundance, and as an indicator for water quality/organic pollution (BMWP). • Fish - biomass, density and species richness. • Birds - the assemblage of breeding birds and abundance

Hydromorphology

• Geomorphology - channel cross sections and physical habitat mapping. • The water quality - suspended sediment concentration, nitrogen and phosphorus. • Modeling flood frequency.

Post- monitoring:

Repetition of pre-monitoring was carried out 1 and 2 years after restoration, as well as a public perception survey. Due to its importance as a demonstration project, further monitoring been carried out by Master and PhD students.

Expectations and results:

It was expected that the new meandering channel would provide better habitat opportunities for aquatic species and the hydromorphology and flood frequency in the floodplain would improve because of the more natural channel dimension.

Ecology

Plant species richness increased immediately after restoration. Marginal emergent plant species richness increased significantly, but submerged aquatic plants showed a less immediate effect. The new upstream channel was quickly recolonized by macro-invertebrates. The downstream reach did not change significantly, but some more niche specific taxa were found 12 years after implementation. Two new species were found in the restored Cole, one stonefly (Leuctra geniculata) and a caddis fly (Athripsodes albifrons) Fish biomass and density returned to pre-restoration levels, and species richness remained unchanged. However, long-term surveys have shown an overall decline in fish density at both restored and control sites, indicating impact from an external factor. The number of breeding wetland species did not increase in the first year. The abundance of Yellow Wagtails (Motacilla flava) increased significantly. Casual inspection suggests little change after two years.

Hydromorphology

The river length was increased by 30%. The cross-sectional area was considerably smaller and less deep. The number of natural in-channel features, such as pools and riffles, increased after restoration. In the downstream section maturing trees also provide woody debris, creating habitats and flow diversity. The restoration measures recreated a more natural flooding regime.

Social

Public perception was measured via a questionnaire and 53% of the respondents in Coleshill mostly approved with the measures while 17% strongly approved. The long-term monitoring showed that only about half of the local residents strongly (25%) or mostly (31%) approved to the river restoration project. The restoration measures showed overall positive results for the ecological status. The downstream channel benefited greatly from the restoration measures, but the new upstream course was not fenced off from cattle and has therefore little riparian vegetation. However, due to lack of initial engagement, some local residents were unhappy with the project.

Lessons learnt

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• Engaging the local community is critical • In these early days of river restoration the project showed what could be expected from a restoration project and how it develops (might be different from anticipated) – this needs to be built into decision making process • It is important to do a formal long-term management plan, and have a cooperating (and stable) land owner • The project showed a whole suite of demonstration techniques (included in the Manual of River Restoration Techniques http://www.therrc.co.uk/rrc_manual.php) • The project clearly showed the complexity of a linear system (compared with pond), and that it's difficult to distinguish success between different components • The project gave a big boost to river restoration in the UK and showed that it is possible to do “large scale” (for that time) projects


Image gallery


Construction of the meanders
Aerial photograph of the restored channel
Bifurcation structure upstream of the mill, March 2005
Cows using the livestock crossing
Crayfish found in the river post-restoration, March 2008
The river during flood conditions, March 2010
ShowHideAdditionalImage.png


Catchment and subcatchment

Catchment

River basin district Thames
River basin Vale of White Horse

Subcatchment

River name Cole (Bower Bridge to Thames) including Coleshill
Area category 100 - 1000 km²
Area (km2)
Maximum altitude category 100 - 200 m
Maximum altitude (m) 148
148 m
0.148 km
14,800 cm
Dominant geology Calcareous
Ecoregion Great Britain
Dominant land cover Arable and Horticulture
Waterbody ID GB106039023730



Site

Name River Cole
WFD water body codes GB106039023730
WFD (national) typology
WFD water body name Cole (Bower Bridge to Thames) including Coleshill
Pre-project morphology Straight, Single channel
Reference morphology Sinuous
Desired post project morphology
Heavily modified water body Yes
National/international site designation
Local/regional site designations
Protected species present No
Invasive species present Yes
Species of interest
Dominant hydrology
Dominant substrate Clay, Silt
River corridor land use Extensive agriculture
Average bankfull channel width category
Average bankfull channel width (m) 11
11 m
0.011 km
1,100 cm
Average bankfull channel depth category 0.5 - 2 m
Average bankfull channel depth (m)
Mean discharge category
Mean annual discharge (m3/s)
Average channel gradient category
Average channel gradient 0.0008
Average unit stream power (W/m2)


Project background

Reach length directly affected (m) 2500 m
2.5 km
250,000 cm
Project started 1993/04/01
Works started 1995/07/01
Works completed 1995/09/01
Project completed 1996/12/31
Total cost category
Total cost (k€) 450
450 k€
450,000 €
Benefit to cost ratio
Funding sources EU LIFE Programme, Environment Agency, National Trust, Countryside Commission, English Nature

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 200
200 k€
200,000 €
Post-project management and maintenance
Monitoring



Reasons for river restoration

Mitigation of a pressure
Hydromorphology Quantity & dynamics of flow, Channel pattern/planform, Width & depth variation
Biology Invertebrates: Abundance, Fish: Species composition
Physico-chemical
Other reasons for the project Habitat diversity, Landscape enhancement


Measures

Structural measures
Bank/bed modifications Planting, Depth variation
Floodplain / River corridor Floodplain spillways
Planform / Channel pattern Creation of secondary channel, Adding sinuosity, Creation of backwater
Other Livestock access, New crossings
Non-structural measures
Management interventions
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
Channel pattern/planform Yes Yes No Yes No Improvement
Width & depth variation No Yes Yes No No Improvement
Flow velocities No Yes Yes No No

Biological quality elements

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

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
Public perceptions No Yes Yes No No No change


Monitoring documents



Additional documents and videos


Additional links and references

Link Description
http://www.therrc.co.uk/case studies/cole brochure.pdf River Restoration Centre Case Study
http://www.therrc.co.uk/rrc publications.php All published documents on the project

Supplementary Information

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