Case study:River Wandle Restoration Project

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Location: 51° 22' 4", -0° 9' 46"
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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


Trout spawning on the Carshalton arm, November 2012, © T. Longstaff (Wandle Trust)
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Catchment and 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) 160
160 m
0.16 km
16,000 cm
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

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

Reach length directly affected (m) 1500
1,500 m
1.5 km
150,000 cm
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

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

Structural measures
Bank/bed modifications Introducing large woody debris, Bank re-grading, Deflectors, Weir removal, Habitat diversification, Restoring riparian vegetation
Floodplain / River corridor Control of invasive species
Planform / Channel pattern Assessment and monitoring program, Channel naturalisation, Re-meandering, Improvement of channel morphology, Weir removal, Creation of fish passes, Channel naturalisation
Other
Non-structural measures
Management interventions
Social measures (incl. engagement) Awareness raising, 'Trout in the Town' project raising the awareness of the river's value in schools, Citizen participation in the restoration project, Community consultation
Other Public consultation, Participation in works, Participation in maintenance


Monitoring

Hydromorphological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Biological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

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

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative


Monitoring documents



Additional documents and videos


Additional links and references

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Supplementary Information

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