Case study:River Wandle Restoration Project
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- 1 Project overview
- 2 Image gallery
- 3 Catchment and subcatchment
- 4 Site
- 5 Project background
- 6 Reasons for river restoration
- 7 Measures
- 8 Monitoring
- 9 Additional documents and videos
- 10 Additional links and references
- 11 Supplementary Information
|Project web site||http://www.wandletrust.org|
|Themes||Fisheries, Habitat and biodiversity, Hydromorphology, Monitoring, Social benefits, Water quality, Urban|
|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
|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|
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
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.
Catchment and subcatchment
Select a catchment/subcatchment
Cost for project phases
Reasons for river restoration
Hydromorphological quality elements
Biological quality elements
Physico-chemical quality elements
Additional documents and videos