Case study:Arborfield nature like bypass and weirs project

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Location: 51° 24' 28.95" N, 0° 55' 27.36" 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	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 weir bypass channel to create free fish migration status, in addition to two backwaters created towards the end of the bypass channel and directly downstream of its exit; as well as creation of 80m of new riffle habitat for spawning.

After twenty years of work, a significant partnership project helping to deliver Water Framework Directive objectives has been completed on the River Loddon at Arborfield, near Reading.

The problem: Arborfield weirs were highlighted as the most significant barrier to fish migration in the Loddon catchment limiting natural habitat types upstream. Local access and flooding issues were raised.

The solution: Two hundred meters of complex channel and backwaters bypassing Arborfield weirs have been created. This will provide some 20km of free fish passage from the River Thames towards Basingstoke at certain times of year for a range of fish like sea trout, barbel and eels. The project delivers enhanced fish spawning and nursery grounds and restores impounded habitat.

The new river channel will help the Loddon towards meeting 'Good Ecological Status' required by the Water Framework Directive (WFD) and aims to be helpful as a case study for similar WFD-led projects around the country.

Project Objectives:

• Working with communities: anglers and local people shaped objectives and gave practical input; University of Reading and Cranfield University are helping with monitoring.
• Allow free fish passage to enable fish to complete lifecycles. We have seen fish entering the channel from top and bottom, confirming the bypass is passable for a variety of small fish.
• Improve Water Framework Directive status from moderate to good: create new fish spawning and nursery areas and monitor effects.
• Restore impounded habitat: lower weirs to restore flow and habitats. Chub have been observed spawning twice on restored riffles upstream since the weirs were lowered.
• Restore Biodiversity Action Plan habitat; construct wet feeds to key areas.
• Provide national case study: ‘before’ and ‘after’ studies to inform others.
• Improve site health and safety: better, safer access around site.
• Local flood risk: lower weirs have reduced breaching to adjacent land.

Works included: Thames Water weir lowering and repair work to four out of five structures - to lower upstream water levels and reduce overbank flow frequency.

Monitoring surveys and results

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Over 1 hectare of nationally important wetland habitats will be restored - benefiting wildlife such as otters, kingfishers and dragonflies. A key feature of the 400k project was the successful partnership with Thames Water, the University of Reading, Farley Estate and Arborleigh Angling Club. Over 60 volunteer days were given

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.

plan

A mosaic of habitats was created in the new river channel, using many existing natural features

The completed bypass inlet in September 2011

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 Introduction of spawning gravels, Riffle creation Floodplain / River corridor Planform / Channel pattern Bypass channel, Improving fish migration, Lowering of weir, Creation of backwater 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) Newsletter November 2011 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.