Case study:River Slea Rehabilitation

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Location: 52° 59' 43", -0° 24' 27"
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Project overview

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Status Complete
Project web site
Themes Habitat and biodiversity, Social benefits, Urban
Country England
Main contact forename Marie
Main contact surname Taylor
Main contact user ID
Contact organisation Lincolnshire Rivers Trust
Contact organisation web site http://www.lincsrivers.org.uk/
Partner organisations Wild Trout Trust
Parent multi-site project
This is a parent project
encompassing the following
projects
No
Section 2 following faggot installation to create berms with the help of volunteers

Project summary

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The River Slea is an 18 mile long tributary of the River Witham, Lincolnshire. The River Slea is groundwater fed from Lincolnshire limestone aquifer and the flow depends on the on groundwater levels. Historically the River Slea flowed all year round. In the early 60s the flow of the river began to slow and ceased in 1962. This was due to a number of reasons such as over abstraction, increase in population and changes in weather cycles. After a public campaign in 1992, a pump was installed by the Environment Agency which delivers groundwater to the river at times of no flow. The Lincolnshire Rivers Trust (LRT) commissioned Clear Environmental to deliver the Sleaford Urban Opportunities Study, which was funded by Natural England. This study highlighted how the river would benefit from various rehabilitation techniques to enable wildlife to be more resilient during low flow periods and also contribute towards WFD objectives. With the help of the Wild Trout Trust, three sections of river were identified where restoration could be completed, this covered approximately 1.2km of river. Unfortunately, due to site constraints, work could only be completed on two sections (sections one and two). There were three phases to the works completed, these are detailed below;

Phase 1: Using an excavator, a low flow channel was created in section one and pools were created in section two. River bed material removed was used to create berms and meanders within the existing channel.

Phase 2: Brushwood bundles were installed, to construct berms which created pinch points, narrowing the channel to speed up the flow and maintain the pools created. This part of the project was made possible with the help of volunteers.

Phase 3: Planting of vegetation using coir matting and plug plants, to increase the rate of colonisation of berms and make them appear more natural.

Monitoring surveys and results

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In September 2015, section one of the river was completely dry, but following the creation of the low flow channel, in September 2016 there was still 1ft of water retained within that section.

Before the works were completed, a water vole survey carried out in 2015 only found old unused burrows, with no signs of water voles. In 2016 another water vole survey was carried out, detecting 12 feeding stations and four latrines.

In 2015 section two was completely uniform with no pools or any habitat features. Following the work, 22 berms were constructed providing cover for fish and providing deeper areas that would help maintain the depth during low flow periods. Planting was successful, and in time, the vegetation will grow and create a natural meandering flow.

Lessons learnt

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Work could not be carried out in section 3 due to the firmness of the riverbed. It is reccomended in the future that the firmness of the riverbed should be tested to ensure habitat improvement works can be carried out. Install coir matting vegetation at the same time as installing brushwood, we had to rely on individual plug plants when planting. Although plugs are cheaper than matting.


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Catchment and subcatchment



Site

Name River Slea
WFD water body codes
WFD (national) typology
WFD water body name
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
Average channel gradient
Average unit stream power (W/m2)


Project background

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Project started
Works started
Works completed
Project completed
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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

Mitigation of a pressure Abstraction
Hydromorphology
Biology
Physico-chemical
Other reasons for the project


Measures

Structural measures
Bank/bed modifications Creation of pools, Creation of berms
Floodplain / River corridor Creation of two stage channel
Planform / Channel pattern Creation of meanders, Channel narrowing, Riparian planting
Other
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

Biological quality elements

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Any other monitoring, e.g. social, economic

Element When monitored Type of monitoring Control site used Result
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Monitoring documents



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Additional links and references

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Supplementary Information

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