15. Grovelands Park Wetlands
Theme: Water quality
Objectives:
- Reduce the frequency and severity of pollution
- Increase surface water management at source
Project description
Part of Thames21's Salmons Brook Health River Challenge
The water system in Grovelands Park, Enfield, has been artificially engineered over time, with the stream being contained in an underground pipe, hidded from view and useless to wildlife. Here beneath the ground two surface water drains from local roads and homes washed pollutants straight into the stream everytime it rained. Plumbing misconnections added to the problem.
In spring 2014, we worked with the London Borough of Enfield to create a Sustainable Drianage System, or Rainscape, to intercept pollutants entering the stream in Grovelands Park. Flows in the surface water drains were diverted into shallow ditches, known as swales, and then into a wetland basin. The swales and basin were planted with sedges suitable for the semi-shaded woodland conditions. The plants use excess nutrients such as phosphates and nitrates to grow, preventing them building up in the water which causes the toxic algal blooms. The plants also oxygenate the water. The clean water then soaks into the ground, as it would naturally, or overflows back into the stream. Rainwater washing of an area the size of 11 rugby fields is cleaned in this rainscape.
At the same time the London Borough of Enfield naturalised the stream, breaking it out of its underground ppipe and allowing it to find its own course meandering through the woodland. These two projects restored the water system to its natural state, better able to cope with floods and slowing high flows of storm water, as well as treating pollutants.