Case study:River Wandle Restoration Project

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Location: 51° 22' 3.71" N, 0° 9' 45.58" W

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Project overview

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Status	Complete
Project web site	http://www.wandletrust.org
Themes	Fisheries, Habitat and biodiversity, Hydromorphology, Monitoring, Social benefits, Water quality, Urban
Country	England
Main contact forename	Tim
Main contact surname	Longstaff
Main contact user ID
Contact organisation	Wandle Trust
Contact organisation web site	http://www.wandletrust.org/
Partner organisations	Environment Agency, Wild Trout Trust, London Borough of Sutton, Defra, Thames Water
This is a parent project encompassing the following projects	Butter Hill Phase 2, River Wandle: Butter Hill Phase 1, River Wandle: Butter Hill Phase 3, River Wandle: Silt & SuDs, Wandle River Restoration Project: Hackbridge

Carshalton Arm Restoration, © Wandle Trust

Project summary

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Historically the River Wandle was a famous chalkstream trout fishery, with the Carshalton arm even lending its name to fishing techniques like the Carshalton Dodge.

The Carshalton arm (a Water Framework Directive waterbody in its own right) in the headwaters was not only identified as strategically important spawning habitat but had the potential to sustain an isolated population if large downstream weirs could not be removed.

However, the 1 km Carshalton waterbody was significantly degraded being overwide, disconnected and impounded by five weirs, over-shaded, contaminated with road runoff, with little habitat variation and limited fish populations. Hence this waterbody was selected for restoration and re-establishment of a wild trout population.

Project Aim: To establish a population of brown trout in the Carshalton arm of the River Wandle for the first time in over 80 years. Objective: To rehabilitate the Carshalton waterbody by improving habitat diversity and quality, fish passage, hydromorphology and water quality; with wild trout used as the indicator species for the river’s recovery.

This Scheme was delivered through a phased approach over six years. A breakdown can be found below of the different phases, with specific project details found on the individual case study pages.

Butter Hill Phase 1: Working in partnership with the Environment Agency, 3 weirs were lowered. Habitat enhancement works were undertaken in the channel with the Wild Trout Trust as part of a practical training day in river restoration techniques for volunteers. A Larinier Fish Pass was installed on a 1.8 m weir downstream.

Butter Hill Phase 2: A small weir which provided a barrier to fish passage and impounded the river for 50 m was notched. This improved fish passage by connecting up 2.5 km of river over two waterbodies. Upstream of the weir, the impounded section was replaced with a narrower channel and marginal shelf which enables the river to be more resilient to low flows and provides a small floodplain in a highly urbanised area.

Butter Hill Phase 3: The weir at ButterHill was reduced in height by 1 m and the fish pass modified to increase efficiency. The length of impounded river was reduced by 150 m (15% of total waterbody length) and fish passage opened up for 500 m upstream (50% of the waterbody length).  A total of 500 m of river was narrowed and meandered with a low flow channel, berms, riffles, pools and marginal wetlands created along the length. Approximately 300 tonnes of gravel were added to restore geomorphology. Volunteers planted 2000 plants and coppiced trees to enhance light penetration.

Silt & SuDs: To reduce urban diffuse pollution, five innovative measures were installed and trialled to determine their effectiveness for mitigation of urban diffuse pollution, particularly road runoff: Downstream Defenders, Siltex, Smart Sponges, Mycofilters and Rain Gardens.

Monitoring surveys and results

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The transformation of the Carshalton arm of the River Wandle is a flagship project for what is possible in an urban environment. With both water and habitat quality having been addressed through the four phases, this section of river has been fully rehabilitated resulting in a diverse and functioning headwater with successful trout recruitment for the first time in over 80 years; achieving the overall project aim and its objectives.

It has just been confirmed (July 2015) that this project has delivered all of the Mitigation Measures required to the enable the Carshalton waterbody to reach Good Ecological Potential.

Fish Data: The EA has a monitoring site for the Carshalton arm at Butter Hill, where much of the work has been carried out. This provides a good time series of fish, invertebrate and plant data.

Environment Agency electrofishing survey results show that there were no wild trout found in the area prior to 2006. Survey results from 2009 and 2011 find low numbers of trout, likely 2+ and 3+ individuals. However following works, in 2015 the story is much different with a Redd count of 10 (increased from 2 in 2012) providing evidence that suitable spawning habitat has been successfully increased. Excitingly, 67 0+ trout were found in the same survey site which shows that fish are not only spawning but successfully recruiting and that optimum juvenile habitat has been created.

EA monitoring shows that other fish species have benefitted from the restoration work. Numbers of bullhead increased from 10-99 in 2011 to 1000+ in 2015. Similarly, three-spined sticklebacks also increased from 100-999 in 2012 to 1000+ in 2015.

Lessons learnt

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Image gallery

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Trout spawning on the Carshalton arm, November 2012, © T. Longstaff (Wandle Trust)

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 London Subcatchment River name Wandle (Carshalton Branch at Carshalton) Area category 10 - 100 km² Area (km2) Maximum altitude category 100 - 200 m Maximum altitude (m) 160160 m <br />0.16 km <br />16,000 cm <br /> Dominant geology Calcareous Ecoregion Great Britain Dominant land cover Suburban Waterbody ID GB106039017640 Other case studies in this subcatchment: Butter Hill Phase 2, River Wandle: Butter Hill Phase 1, River Wandle: Silt & SuDs, Wandle River Restoration Project: Hackbridge Site Edit site Name Butter Hill, Carshalton WFD water body codes GB106039017640 WFD (national) typology Low, Small, Calcareous WFD water body name Wandle (Carshalton Branch at Carshalton) Pre-project morphology Over deepened, Over-widened, Ponded, Straightened Reference morphology Pool-riffle Desired post project morphology Heavily modified water body Yes National/international site designation Local/regional site designations Protected species present No Invasive species present No Species of interest Dominant hydrology Flashy, Artificially regulated Dominant substrate Gravel, Silt, Bedrock River corridor land use Average bankfull channel width category 2 - 5 m Average bankfull channel width (m) Average bankfull channel depth category 0.5 - 2 m Average bankfull channel depth (m) Mean discharge category 1 - 10 m³/s 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) 15001,500 m <br />1.5 km <br />150,000 cm <br /> Project started 2008/01/01 Works started 2010/01/01 Works completed 2012/09/01 Project completed 2012/12/01 Total cost category Total cost (k€) 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 Flood risk management, Barriers to fish migration Hydromorphology Channel pattern/planform, Continuity of sediment transport, Quantity & dynamics of flow, Substrate conditions, Width & depth variation Biology Invertebrates, Fish Physico-chemical Temperature Other reasons for the project Community demand Measures Edit Measures Structural measures Bank/bed modifications Introducting large woody debris, Bank re-grading, Creation of deflectors, Removal of weirs, Habitat diversification, Restoring riparian vegetation Floodplain / River corridor Control of invasive species Planform / Channel pattern Allow future natural channel changes to occur, Assessment and monitoring program, Channel naturalisation; Creation of new meandering channel, Establishment of fish passage, Improvement of channel morphology, Removal of a weir Other Non-structural measures Management interventions Social measures (incl. engagement) Awareness campaigns, 'Trout in the Town' project raising the awareness of the river's value in schools, Citizen participation in the restoration project, Communication and dissemination program of environmental problems in the area Other Public consultation, Participation in works, Participation in maintenance 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 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 Supplementary Information Edit Supplementary Information