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.

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

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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

Catchment and subcatchment Select a catchment/subcatchment Edit the catchment and subcatchment details (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 Edit 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) 5.55.5 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 Edit project background 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 Edit reasons for restoration Mitigation of a pressure Hydromorphology Channel pattern/planform Biology Fish Physico-chemical Other reasons for the project Measures Edit 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 Edit Hydromorphological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Biological quality elements Edit 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 Edit 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 Edit Other responses Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Monitoring documents Upload monitoring documents Additional documents and videos Upload additional documents Additional links and references Edit 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 Edit Supplementary Information