South East Rivers Trust (& the Wandle Trust)

Wetland creation to help the Hogsmill

Latest news on the Chamber Mead wetland creation project.

The Chamber Mead project will breathe life back into the Hogsmill by creating a new wetland habitat that will help clean contaminated water before it enters the river. The Green Lanes Stream joins the Hogsmill just a few hundred metres from its spring source, but brings with it high levels of polluting substances. By creating a series of wetlands through Chamber Mead, this project will allow natural cleaning processes to reduce the impact of sewage and urban pollution on the Hogsmill. 

Why do we need a wetland?

The Hogsmill is one of only 200 chalk streams in the entire world. These special rivers are renowned for their crystal clear waters and extremely high quality water. This means that when in a healthy condition, these rivers support a wonderful array of wildlife, which can only thrive in these rare, pollution-free streams.

Unfortunately, the Hogsmill cannot reach its spectacular potential as it suffers from the chronic pollution issues that affect many urban rivers. Oil, dirt and a cocktail of toxic substances are washed off surrounding roads straight into the river each time it rains. Sewage makes its way into the Hogsmill from a worrying array of sources, which pose a danger to people’s health as well as negatively affecting the river’s wildlife. The Green Lanes Stream, a tributary of the Hogsmill, is a particular hotspot for these kinds of pollution.

The Green Lanes Stream is a hot spot for pollutants including oil and sewage.

Many options for reducing the input of pollutants from the Green Lanes Stream into the Hogsmill have been explored by the Hogsmill Catchment Partnership. Creating a series of wetlands at Chamber Mead is the preferred solution, as this will work with natural processes to achieve this aim, as well as producing many other benefits for people and wildlife.

How do we know a wetland will work?

Constructed wetlands make use of the natural purification processes of vegetation, soils and microbes to remove polluting substances.

As dirt is washed off roads, it will settle at the bottom of the wetland after reaching an area of slow water flow, reducing the input to the Hogsmill. Excess nutrients from sewage inputs will be absorbed and stored by wetland plants, and chemicals including oil will be broken down by micro-organisms.

These are well studied natural processes, and the wonders of wetlands are being used all over the world in similar projects. Many sewage treatment works are also constructing wetlands to treat the water they discharge further before it reaches the river.

How will Chamber Mead change?

The Green Lanes Stream will be diverted to flow diagonally across Chamber Mead, re-joining the Hogsmill just downstream of the Stepping Stones. Along its new path will be a series of wetland basins, planted with native wetland vegetation to remove pollutants from the water.

Site plan of Chamber Mead Wetland.
Light blue shows current path of the Green Lanes Stream.
Dark blue shows new wetland areas.
Brown outline shows area where excavated material may be spread to reduce the number of lorry loads removed from site.

By doing this, not only will the water quality be improved, but the wetland will boost biodiversity within the Hogsmill Local Nature Reserve. The new habitat created will be the ideal place for amphibians like frogs and newts, colourful dragonflies and other aquatic plants and animals.

Creating this wonderful wetland habitat will involve significant groundworks which will leave large areas of bare earth immediately after digging is complete. However, these will green up very quickly as areas of grass will be re-seeded and over 10,000 wetland plants will be added. The area may be fenced off initially to give this new vegetation time to root.

A similar wetland scheme in Tonbridge.

The wetland will provide a valuable educational resource for local schools with free lessons run by the South East Rivers Trust in the months after completion. New dipping platforms, a bridge and family activity trail will maintain and enhance access to the space, making it a valued part of the Hogsmill Local Nature Reserve for years to come.

The popular paddling spot round the Stepping Stones will be maintained and thanks to the new wetland, the water quality here will be much better, reducing the risk to public health.

When is this happening?

Delivery of the work is planned to take place over an 8 week period in the summer of 2021. An application for planning permission is expected in early 2021.

Will there be disruption during work?

Yes – we are afraid there will be some disruption to local residents and park users during construction of the wetland. We are extremely sorry for any inconvenience this will cause, but we’re doing everything we can to minimise the disruption.

The use of heavy machinery to excavate the wetlands will make it necessary to close some paths temporarily for the safety of those visiting Chamber Mead. This will be done for the minimum possible duration and a suitable alternative diversion will be put in place.

Once excavated, a large quantity of earth will need to be removed from site in lorries. It is highly probable that access to and from Chamber Mead will be along Green Lanes which is likely to cause disturbance to local residents. We are doing our best to reduce the number of lorry loads required by gaining permission to spread some of the earth on site. However, it’s likely there will still need to be a significant number of lorries involved. Work of this nature will never occur at weekends or at anti-social hours but is likely to have to take place over several weeks.

We hope the wetland we create, and the benefits it will bring to the Hogsmill, its wildlife and local residents, will make up for this short-term disturbance.

Will there be opportunities to get involved with the work?

There will be plenty of opportunities to get involved in different stages of the project including planting wetland vegetation, removing plastic pollution and further habitat enhancement as the wetland matures.

The South East Rivers Trust will be working with local schools to run outdoor learning sessions at the wetland. If you’re a teacher at a nearby school and you’d like your class to be involved – please contact the project team on

What has happened to date?

This project has been planned and developed over several years in conjunction with Epsom and Ewell Borough Council. The need for wetland creation to clean up contaminated water from the Green Lanes Stream is highlighted in the Council’s 100 year plan for the Hogsmill Local Nature Reserve, and the project is supported by members of the Hogsmill Catchment Partnership.

Part of the development process has been carrying out extensive flood modelling to ensure that creating the wetland does not increase flood risk upstream. Ground investigations have confirmed the site is suitable for conversion to wetland and a design has been drawn up with advice from wetland experts. The South East Rivers Trust has now successfully gained funding to progress this project and complete delivery of this ambitious project.

How can I find out more?

If you have any questions at all about the Chamber Mead Wetland project, or would like to discuss any concerns you have with a member of the project team, please email us on

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Have any Question or Comment?

9 comments on “Wetland creation to help the Hogsmill

leonard grover

Get the council to sort the parking out in Greenlanes before you start running lorrys down to Chamber mead. All that is needed is restricted parking times to stop cars parking to use as a free stop for West Ewell railway station, instead of using the charged car park at the station.

leonard grover

Await reply.

Jess Mead

Dear Leonard, thank you for getting in touch and I understand your frustration with parking. However, changes to parking restrictions are completely out of our control I am afraid. You can always visit the Surrey County Council website and request a change to parking restrictions here:
I hope that helps and please do feel free to drop us an email at if you have any more questions.

William Brown

After reading about the proposedChamberMead project I feel part of the pollution of the Green Lanes stream could be the flood outlet on the Longmead Road just near the church. This outlet has always shown signs of pollution and has in the past been investigated but never been rectified. If this source of the pollution could be rectified it could help in ensure cleaner water running into the Hogsmill River

Jackie Dodd

I would love to help with planting up when needed and have friends who might help too.

Mike Davis

I note the request for local schools to get involved.
Is there an opportunity for those of us retired and with the appropriate skills to assist in the project?

Jess Mead

Hi Jackie, there will be lots of opportunities to get involved with the project over the coming year (Covid restrictions permitting). The best thing to do is sign up to our mailing list at as this is where we send out information about all of our upcoming volunteer opportunities. Hope to see you along to one of our volunteer days in the near future.

Jess Mead

Hi Mike, there will be lots of opportunities to get involved with the project over the coming year (Covid restrictions permitting). The best thing to do is sign up to our mailing list at as this is where we send out information about all of our upcoming volunteer opportunities. Hope to see you along to one of our volunteer days in the near future.

Jess Mead

Dear William, thank you for getting in touch. There are many outfalls along the Green Lanes Stream and I am afraid I am unsure about exactly which one you are referring to. Please can you email with more of a description of the location, a photo of the outfall or a map with it marked on and we can then hopefully give you an update on what has been done to date. Or if it’s an outfall we’ve not brought to Thames Water’s attention so far, we can make sure we do that. Thanks.

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