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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(affects all case studies in this 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)	122122 m <br />0.122 km <br />12,200 cm <br />
Dominant geology	Calcareous
Ecoregion	Great Britain
Dominant land cover	Arable and Horticulture
Waterbody ID	GB104027063173

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

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

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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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Image gallery

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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

Additional documents and videos

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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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