Wetland Saved From Highways Pollution

A precious part of London’s remaining medieval common land has been saved from the threat of pollution from nearby highways with a simple solution using Hydro’s Downstream Defender®.

Mouchel Parkman, on behalf of the Highways Agency, contacted Hydro about the innovative hydrodynamic vortex separation device that saved Shortwood Pond, a Site of Special Scientific Interest, from serious pollution damage.

The precarious wetland habitat at Shortwood Pond off the A308 by the Crooked Billet Roundabout is home to endangered species such as the Brown Galingale plant and the Little Whirlpool Ramshorn snail. It is part of Staines Moor, located at the eastern end of Colne Valley Park, which contains many Sites of Special Scientific Interest.

Project engineer David Funchal, of Mouchel Parkman, explains: “The Victorian-dug Shortwood Pond is a chalk spring-fed water with no outlet.  Road drainage work in the 1970s directed stormwater runoff into the pond and, in recent years, water quality has been declining, with an increase in black globular sediment smelling strongly of hydrocarbons.

“Increasing traffic contributes to this pollution, and there was also no protection from a major spillage event.  Working with Hydro, we found the Downstream Defender® was ideally suited to protecting the pond, because it separates out and retains the sediments. The entrapped solids and sediments are not washed out by high storm flows as they would be in conventional gully pots. The hydrocarbons and floatable portions are also retained.

“The project was completed within a tight budget and kept to a small footprint.  Apart from chamber emptying, maintenance is minimal. In fact we were able to oversize it to allow for up to 50 l/s and help protect the site against future large storm events”.

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