Case study:River Dearne at Mexborough

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Location: 53° 30' 14", -1° 15' 20"
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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.

Reduced maintenance (est. £2, 500-£3, 000 reduction in maintenance costs per year)

Monitoring surveys and results

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Lessons learnt

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Image gallery


Canalised reach before restoration works
Placement of limestone boulders and berm back-filling
New sinuous reed-fringed course following restoration
Narrowed channel with increased velocities and riffles for fish spawning
Main channel and back water five years on, 2000
Main channel and operational backwater, 2012
Silted backwater channel, 2012
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Catchment and subcatchment

Catchment

River basin district Humber
River basin Don and Rother

Subcatchment

River name River Dearne Darfield STW to River Don
Area category 100 - 1000 km²
Area (km2)
Maximum altitude category 100 - 200 m
Maximum altitude (m) 122
122 m
0.122 km
12,200 cm
Dominant geology Calcareous
Ecoregion Great Britain
Dominant land cover Arable and Horticulture
Waterbody ID GB104027063173



Site

Name River Dearne at Mexborough
WFD water body codes GB104027063173
WFD (national) typology
WFD water body name River Dearne Darfield STW to River Don
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) 5.5
5.5 m
0.0055 km
550 cm
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

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

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
Hydromorphology Channel pattern/planform
Biology Fish
Physico-chemical
Other reasons for the project


Measures

Structural measures
Bank/bed modifications Adding sinuosity
Floodplain / River corridor Creation of backwaters
Planform / Channel pattern Channel narrowing, Creation of backwater
Other
Non-structural measures
Management interventions Reduced maintenance
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
Fish: Abundance Yes Yes Yes Yes No Improvement

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/pdf/manual/MAN 3 6.pdf RRC Manual of River Restoration Techniques entry

Supplementary Information

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