A beautiful community landscape featuring new wetland basins, nested between trees, to treat polluted water, has been created from what was a neglected, rubbish-strewn and highly polluted stream corridor.
This project demonstrates how community and public spaces in urban areas can be designed to clean heavily polluted urban waterways and simultaneously to enhance landscapes for the enjoyment of local people and wildlife. The involvement of the community in the development, implementation and maintenance of the project can provide a sense of ownership of the space which helps to ensure its long term viability. This involvement also serves to inform the public of the reality of waste and pollution in their immediate environment that might otherwise remain unnoticed.
Before the creation of our ‘SuDS Park’, this ribbon of woodland to either side of the stream was a no-go area. The public perception was that it was good for wildlife but also a site for antisocial behaviour.
At the same time as working to improve the water quality of the stream, we wanted to make the landscape more friendly and inviting to the local community and to wildlife. In order to establish a healthy population of plant species and friendly pollution-munching microbes within the treatment wetlands, we needed to thin the woodland in places to let more light into the woodland floor. This also makes the woodland more inviting and improves its diversity of flora and fauna.
The wetland basins have been designed to blend into the existing landscape as much as possible. We have improved the profile of what was a deeply-incised stream and provided stepping-stone and weir crossing points to improve access.
The local community was involved through the development of the project and have developed a sense of ownership through scrub clearance and wetland planting days and we are hopeful that informal paths will develop as people enjoy the improved environment and extra wildlife attracted to the wetlands.
The stream receives flows from surface water drains as well as numerous domestic mis-connections, resulting in a highly polluted watercourse that is subject to flashy flow patterns. It emerges from a culvert into the woodland landscape where we have lifted its base level and created a series of weirs diverting low-flows into wetland basins that treat the water to remove pollutants. Each wetland 'cell' filters and treats the polluted water making it a little cleaner step by step as it travels along the wooded valley.
The weirs allow larger flows that occur in storms to continue along the original stream channel but catch the first flush in the wetland cells.
The treatment of pollutants occurs by particles settling to the bottom of the wetland areas as the water travels more slowly, and by 'bioremediation' whereby microbes and plants convert the pollution into harmless substances.
Monitoring by Thames21 in 2012-2013 identified elevated levels of ammonia, nitrate, faecal coliforms and phosphorus in the watercourse.
Within the Enfield area it is estimated that up to 10% of all properties have misconnections. In the areas upstream of Glenbrook this figure has been identified as being approximately 5% of all properties (55 dwellings).
To achieve ideal levels of pollutants at the end of the system, more than 1100m2 of dedicated treatment wetland would be required.
It has been possible to sensitively create approximately 700m2 of wetland treatment areas within the landscape which is enough to have a significant impact on pollution levels. Thames21 & Thames Water will continue to tackle misconnections to further improve water quality outcomes and ongoing monitoring by Thames21 will determine the efficacy of the system.