Case study:River Dearne at Mexborough

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Location: 53° 30' 14.25" N, 1° 15' 20.14" W
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Project overview

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Status Complete
Project web site
Themes Fisheries, Flood risk management, Habitat and biodiversity
Country England
Main contact forename Chris
Main contact surname Firth
Main contact user ID
Contact organisation Don Catchment Rivers Trust
Contact organisation web site http://www.dcrt.org.uk/
Partner organisations
Parent multi-site project
This is a parent project
encompassing the following
projects
No
Site plan for the restored reach

Project summary

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The lower River Dearne had suffered substantial changes to its natural gradient as a result of subsidence problems cause by deep mining operations. To alleviate this problem a new straight and over-wide river was created in the 1970s to ensure efficient evacuation of floodwaters. This resulted in physical uniformity of the channel, poor water quality and a lack of habitats for fish and other species.

The restoration scheme drastically reduced the width of the channel (10m to 5.5m) by creating a sinuous course and low flow channel using large boulders to create berms. Flood capacity was maintained by ensuring the in-channel structures were kept to a low level and the berms were designed to be submerged during high flow events. The design included three small backwaters and scrapes and the low berms were created at a variety of levels to enable the establishment of a range of riparian communities and provide habitats for a range of species.

Monitoring surveys and results

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Lessons learnt

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Catchment and subcatchment

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Site

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Name River Dearne at Mexborough
WFD water body codes GB104027063173
WFD (national) typology
WFD water body name
Pre-project morphology Straightened, Over-widened, Uniform
Reference morphology Sinuous, narrower low flow channel
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 Gravel
River corridor land use Agriculture (arable)
Average bankfull channel width category
Average bankfull channel width (m) 5.55.5 m <br />0.0055 km <br />550 cm <br />
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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Reach length directly affected (m) 500500 m <br />0.5 km <br />50,000 cm <br />
Project started 1995/05/01
Works started
Works completed
Project completed 1995/09/01
Total cost category 10 - 50 k€
Total cost (k€) £43,000"£" is not declared as a valid unit of measurement for this property.
Benefit to cost ratio
Funding sources

Cost for project phases

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Investigation and design
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Works and works supervision
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Monitoring



Reasons for river restoration

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Mitigation of a pressure
Hydromorphology Channel pattern/planform
Biology Fish
Physico-chemical
Other reasons for the project


Measures

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Structural measures
Bank/bed modifications Adding sinuosity
Floodplain / River corridor Creation of backwaters
Planform / Channel pattern Backwaters created, Channel narrowing
Other
Non-structural measures
Management interventions Reduced maintenance (est. £2, 500-£3, 000 reduction in maintenance costs per year)
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
Fish: Abundance Yes Yes Yes Yes No Improvement

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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Additional links and references

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Link Description
http://www.therrc.co.uk/pdf/manual/MAN 3 6.pdf RRC Manual of River Restoration Techniques entry

Supplementary Information

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