Case study:Arborfield nature like bypass and weirs project

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Location: 51° 24' 19.55" N, 0° 55' 42.70" W

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Project overview

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Status	Complete
Project web site
Themes	Flood risk management, Habitat and biodiversity
Country	England
Main contact forename	Dominic
Main contact surname	Martyn
Main contact user ID
Contact organisation	Environment Agency
Contact organisation web site	http://www.environment-agency.gov.uk
Partner organisations
Parent multi-site project
This is a parent project encompassing the following projects	No

One of the five weir structures to be lowered during the project - pre-works. Courtesy of Wild Trout Trust and the Environment Agency.

Project summary

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In this reach, impassable flow control structures impounded the river by 1.4m, for over 4km upstream. WFD fisheries surveys determined moderate to poor ecological status upstream of the structures, with good ecological status downstream.

Project objectives to improve WFD status upstream of weir structures from 'moderate' to 'good', along with flood alleviation. Works involved lowering of 5 structures along an 800m section of river, construction of a 200m nature-like bypass channel, in addition to two backwaters and creation of 80m of new riffle habitat for spawning.

Monitoring surveys and results

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Lessons learnt

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Image gallery

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Small fixed-crest weir prior to lowering. Courtesy of Wild Trout Trust and the Environment Agency.

Small fixed-crest weir after lowering. Courtesy of Wild Trout Trust and the Environment Agency.

Backwater effect - 900m upstream of impounding weir structures. Courtesy of Wild Trout Trust and the Environment Agency.

900m upstream of lowered impounding weir structures. Note significant reduction in backwater effect. Courtesy of Wild Trout Trust and the Environment Agency.

Channel 2900m upstream of impounding weir structures, prior to lowering. Courtesy of Wild Trout Trust and the Environment Agency.

Channel 2900m upstream of lowered impounding weir structures. Note significant driop in water level and exposure of gravel riffle - now spawned on by chub. Courtesy of Wild Trout Trust and the Environment Agency.

Catchment and subcatchment Select a catchment/subcatchment Edit the catchment and subcatchment details (affects all case studies in this subcatchment) Catchment River basin district Thames River basin Loddon Subcatchment River name Loddon (Swallowfield to River Thames confluence) Area category 100 - 1000 km² Area (km2) Maximum altitude category Less than 100 m Maximum altitude (m) 9999 m <br />0.099 km <br />9,900 cm <br /> Dominant geology Calcareous Ecoregion Great Britain Dominant land cover Suburban Waterbody ID GB106039023160 Site Edit site Name Loddon at Arborfield WFD water body codes GB106039023160 WFD (national) typology Low, Medium, Calcareous WFD water body name Loddon (Swallowfield to River Thames confluence) 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 Target fish species: sea trout, eels, dace, barbel, chub, roach, bullhead, lamprey and pike. 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 1 - 10 m³/s Mean annual discharge (m3/s) 2.162.16 m³/s <br />2,160 l/s <br /> Average channel gradient category Average channel gradient Average unit stream power (W/m2) Project background Edit project background Reach length directly affected (m) 800800 m <br />0.8 km <br />80,000 cm <br /> Project started 2010/06/30 Works started Works completed 2011/07/06 Project completed Total cost category more than 10000 k€ Total cost (k€) 596596 k€ <br />596,000 € <br /> Benefit to cost ratio Funding sources DEFRA, Environment Agency FCRM and Fisheries, Thames Water, Barbel Society Cost for project phases Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname Investigation and design 100 - 500 k€ 120120 k€ <br />120,000 € <br /> Stakeholder engagement and communication Works and works supervision 100 - 500 k€ 450450 k€ <br />450,000 € <br /> Post-project management and maintenance Monitoring 10 - 50 k€ 2424 k€ <br />24,000 € <br /> Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Barriers to fish migration, Flood risk management Hydromorphology Biology Fish Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Creation of 80m of (riffle habitat) spawning gravels. Floodplain / River corridor Thames Water weir lowering and repair work to four out of five structures - to lower upstream water levels and reduce overbank flow frequency. Planform / Channel pattern Construction of 200m weir bypass channel to create free fish migration status. Two backwater areas created towards the end of the bypass channel and directly downstream of its exit. Other Non-structural measures Management interventions Social measures (incl. engagement) Other Presentations and meetings with local citizens. Volunteers involved in construction and future management of project. Monitoring Hydromorphological quality elements Edit Hydromorphological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Channel pattern/planform Yes Yes No Yes No Awaiting results Quantity & dynamics of flow Yes Yes No Yes No Awaiting results Biological quality elements Edit biological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Fish Yes Yes Yes Yes Yes Awaiting results Invertebrates Yes Yes No Yes No Awaiting results Macrophytes Yes Yes No Yes No Awaiting results 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 Habitat mapping Yes Yes Yes Yes No Awaiting results Monitoring documents Upload monitoring documents Additional documents and videos Upload additional documents Photo update from October 2012 (courtesy of Dominic Martyn) Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information Post-project ecological/hydromorphological monitoring assessments during 2011/12. Data should be available during 2012.