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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Catchment and subcatchment

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(affects all case studies in this subcatchment)

Site

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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

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Reach length directly affected (m)	800m0.8 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€)	~596"~" is not declared as a valid unit of measurement for this property.
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€	~450"~" is not declared as a valid unit of measurement for this property.
Post-project management and maintenance
Monitoring	10 - 50 k€	2424 k€ <br />24,000 € <br />

Reasons for river restoration

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Mitigation of a pressure	Barriers to fish migration, Flood risk management
Hydromorphology
Biology	Fish
Physico-chemical
Other reasons for the project

Measures

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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

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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

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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

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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
Habitat mapping	Yes	Yes	Yes	Yes	No	Awaiting results

Monitoring documents

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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.

Additional documents and videos

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Photo update from October 2012 (courtesy of Dominic Martyn)

Additional links and references

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Link	Description

Supplementary Information

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Post-project ecological/hydromorphological monitoring assessments during 2011/12. Data should be available during 2012.