14. Houndsden Road Raingardens

Theme: Water quality


  • Reduce the frequency and severity of pollution
  • Increase surface water management at source

Project description

Part of Thames21's Salmons Brook Healthy River Challenge


The Houndsden Gutter is a tributary of the Salmons Brook, a small river runing through Enfield which joins the Lea Navigation. Like many urban streams it suffers from pollution. Oils and heavy metals off the roads when it rains, flowing into surface water drains which lead straight  into our streams and rivers.  The plumbing in some homes and businesses is misconnected, sending water from appliances, sinks and sometimes even toilets into watercourses instead of sewers. As a result the Houndsden Gutter sadly lives up to its name.


In autumn 2015 we worked with the London Borough of Enfield to create two SuDS to improve the water quality in the stream. They have been designed to treat water that runs of Houndsden Road every time it rains. In the first system run-off is directed along the verge in a shallow ditch known as a swale and into the natural woodland basin of the Spinney, where chemicals which would pollute the river are naturally and safely used by plants to grow or broken down by bacteria in the soil. The swales have been planted with sedges and native grasses to slow water flow and begin the treatment, and the woodland basin planted with suitable native seed mixes. Water will then naturally soak into the soil, recharging  the water table. This is particularly important during times of summer  drought. The second system works on the same principle, diverting road run-off through swales and two planted basins, with capacity for an overflow route during times of very heavy rainfall. These SuDS prevent oils and heavy metals washing into the Houndsden Gutter. The stream supports a small fish population, and fish are seriously impacted by such pollutants, so reducing the pollutant levels in the stream is of great importance.




Project lead: Thames21
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Design by LTD Design Consultants and build by Garganey Consulting.