South East Rivers Trust

Chamber Mead Community Wetland Proposal

The Hogsmill – a Chalk Stream in crisis

The Hogsmill is classified as a chalk stream, a globally rare habitat, and one of around only 200 worldwide. Chalk streams give rise to a unique set of species that depend on the clean, chalk-purified water and are consequently very sensitive to any decline in water quality.  The Hogsmill is an important asset for the community, with the stepping stones within the Hogsmill Local Nature Reserve in particular used heavily by children, families and dog walkers.

The Green Lanes Stream enters the Hogsmill a few hundred metres downstream from the main river’s source, adjacent to a two-acre meadow known as Chamber Mead. The Green Lanes Stream has very flashy characteristics as a consequence of draining Epsom town centre, the surrounding roads and the Longmead Industrial Estate. During heavy rainfall the river can also be impacted by discharges of untreated sewage and storm water from the Epsom Storm Tanks, and polluted runoff from roads and other hard surfaces common in urban areas.

Example of poor water quality on the Green Lanes Stream. Oil, sewage fungus and sewage “rag” evident.

As a result of this, the water quality in the river is poor, with long running and recurring pollution incidents. This has been identified as a problem for both the Green Lanes Stream and the Hogsmill River, into which the stream flows, as evidenced through Environment Agency water quality testing. The Hogsmill is unhealthy and polluted, to the detriment of aquatic flora and fauna. This pollution also poses a public health risk to children who play in the river, as well as to dogs and their owners.

Downstream of Chamber Mead, the Hogsmill continues to flow through 2.5km of heavily used public green space, where children frequently paddle and dogs swim, unaware of the water quality issues. Improvements in water quality will improve this current public health issue, making it a safer place for everyone in the local community.  

Chamber Mead – the amenity grassland area at he end of Green Lanes, Ewell. Closest postcode KT19 9SZ.

The Proposed Solution

Given the Hogsmill’s global importance, the South East Rivers Trust has been working hard to protect and restore the river for both communities and wildlife. For example, the Trust hosts the Hogsmill Catchment Partnership which brings together local stakeholders (businesses, NGOs, local government and members of the community) to understand how the river has been changed and impacted; to identify solutions; and to develop projects aimed at improving the health of the river. The Hogsmill Catchment Partnership vision “is for the Hogsmill to be a clean river, rich in biodiversity, that is a resource for an engaged local community.”

A collaborative project between the Hogsmill Catchment Partnership, the Environment Agency and Epsom and Ewell Borough Council is currently underway, led by the South East Rivers Trust. The partners are undertaking a feasibility study investigating how water quality from the Green Lanes Stream can be improved, at the same time as improving open space within the Local Nature Reserve for people and wildlife.

The favoured option involves diverting the Green Lanes Stream through Chamber Mead meadow. The new channel would follow a winding path, passing through a constructed sediment trap and wetlands, before joining the Hogsmill River approximately 200 metres further downstream of where the Green Lanes Stream currently flows into the Hogsmill. Interpretation boards will be installed to spread awareness and understanding of the Hogsmill, the pressures it faces and the work being carried out to tackle this.

A plan of the proposed community wetland – the light blue line is the current flow path of the Green Lanes Stream as it meets the Hogsmill. The dark blue is the proposed diversion.
Examples of similar wetland projects. Left: Wetland within Grosvenor and Hilbert Park, Royal Tunbridge Wells. Right: Richmond Park Golf Course wetland.

What’s so great about a wetland?

The project will bring multiple benefits to the Hogsmill’s health and ecology, provide varied habitat and increase biodiversity, benefit public health and boost local amenity value.

  • Improved water quality: a level of treatment of contaminants through settling of contaminated sediment in the wetlands and physical, biological and chemical processes;
  • Up to 1,000m2 of wetland habitat created: boosting diversity of habitat within the Hogsmill Local Nature Reserve;
A banded damoiselle resting on wetland plants.
  • An extra 200m of un-impacted chalk stream habitat: part of the Hogsmill River will be protected from the influence of the Green Lane Stream’s flashiness and poor water quality, benefiting flora and fauna;
  • Improvements to public health: along a section of the Hogsmill including the stepping stones, which are popular with children for paddling as well as dogs;
The Stepping Stones area is a popular paddling and playing spot for families and dogs.
  • 200m of chalk stream habitat enhanced: habitat restoration works will be carried out along a section of the Hogsmill as part of the project;
  • Increased aesthetics: reduced visible pollution;
  • Improved community amenity: the new wetlands will be an attractive addition to the Hogsmill Local Nature Reserve. Interpretation boards will enhance public appreciation of the Hogsmill and the pressures impacting it;
An example of an interpretation board erected as part of a similar wetland restoration project.
  • Educational facilities: the wetland habitat offers educational opportunities for local schools.
  • Flood risk mitigation: the project will form an important part of a catchment-scale approach to mitigate against flooding, by providing storage during heavy rain events.

Have any Question or Comment?

7 comments on “Chamber Mead Community Wetland Proposal


What will happen to the steam running through Green Lanes?


Why does the diverted water rejoin the stream after the stepping stones
This will leave the stones high and dry in the summer and spoil the enjoyment for all visitors of this feature.
Would it not be better to rejoin the stream before the stepping stones?

Jess Mead

Hello, The stream as it runs along Green Lanes will remain as it is now. The only change is that instead of running straight into the Hogsmill at the current confluence it will flow diagonally across the Chamber Mead Meadow, though some wetlands which will cleanup the water. It will then rejoin the Hogsmill just downstream of the stepping stones.

Jess Mead

Hi Judy,
The reason we’ve designed the project this way is that, at the moment, after heavy rains there are some storm overflow tanks that discharge raw sewage into the Green Lanes Stream. You can read more about them HERE. This means that after summer storms, children could be playing at the stepping stones in water contaminated with sewage. Although the wetland we propose will help cleanup some of this, because of this high flows experienced when the tanks discharge some of it will still be flowing into the Hogsmill under these conditions. So we wanted to make sure that we removed the risk of contaminated water from the stepping stones area which will have a positive benefit on public health.
It is true, as you say, that there will be reduced water volumes in this section of the Hogsmill, though we hope that this will not reduce people’s ability to enjoy the area. Low flows in chalk streams are a problem throughout the South East at the moment, as we are abstracting more water from the underground reservoirs that feed them, than the rainfall is replenishing. This problem seems to have got worse on the Hogsmill in the last couple of years. To try and improve this situation, we are working hard with other members of the Hogsmill Catchment Partnership to put pressure on the Water Companies that are profiting from the abstraction, to try and make sure they are having less of a negative impact on the environment.
If you have any more questions then please don’t hesitate to get in touch.

Grant Woolven

When is this going to happen?

Jess Mead

Hello Grant, there is no definite timeline at the moment. However it will take place in either the summer of 2020 or summer of 2021.

[…] Exciting proposals for a new wetland on South London’s Hogsmill River, as development plans progress for one of the Wandle’s worst fly-tipping blackspots […]

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