So you know that the roads can be pretty dirty. You see the direct effects of it on your car when you think it’s probably time to give it a clean. The dirt on the roads is also really well illustrated when it snows and soon the pure white snow changes to black slush. But where does all of this dirt come from?
You see trucks and lorries leaking oil and busses belching out thick clouds of exhaust fumes when pulling away from traffic lights. You see gulley pots full of litter, cigarette butts and sand that has run off the nearest building site. Or the paint that is dripped out of vans or has been poured into the curb. You walk along the street dodging ‘dog eggs’ which litter the pavement. Then in winter the roads get spread with grit and salt during cold snaps.
You may consider of all of these things as unsightly or unpleasant when on the roads, but within a short period of time and with a bit of rain, all of these substances are washed away and are out of sight and out of mind. But where does it disappear to?
The answer: often the nearest watercourse.
The initial runoff, known as the ‘first flush’, runs black especially in urban areas. In turn with many other outfalls also discharging the entire river turns black.
First flush on the River Wandle, South East Rivers Trust
So what is in this run-off?
Basically it consists of a nasty cocktail containing pieces of the road surface, tyres, brake pads and other material from engine parts from regular wear. Throw into the mix some fuel, gear oil, grease, brake fluid and antifreeze. Then for good measure add some pesticides, fertilisers, plant detritus, some illicit dumping of substances, inputs from misconnected drains and in winter de-icing grit and salt.
Unsurprisingly road runoff can be detrimental to the receiving watercourse, whose impacts on riverine ecology can be acute or chronic. The sediment smothers gravels vital for invertebrates and fish. The turbid water reduces light penetration so plant communities suffer due to limited photosynthesis. Furthermore, the sediment blocks the feeding mechanisms of filter feeders and gills of other aquatic organisms.
The Poly Aromatic Hydrocarbons (PAHs) (oils) and heavy metals are both known to be toxic to aquatic fauna. High concentrations of heavy metals associated with the ‘first flush’ can ‘shock’ aquatic environments as the water is polluted with levels several times higher the normal concentration. Multiple studies have shown that heavy metals can also cause long term impacts as they bio-accumulate within the food chain.
So what can we do?
It is well known that these contaminants freely bind to sediment. It therefore follows that if the sediment is removed, so too will many of the contaminants. This is the plan to protect the Beverley Brook in Richmond Park.
The Rivers Trust and WWF are managing three water management projects in the Thames and South East River Basins, for the benefit of both people and wildlife. The wider initiative is funded by the Coca-Cola Foundation and contributes to Coca-Cola’s promise to safely return the full amount of water used in finished beverages and their production to communities and nature by 2020 – an ongoing commitment as they managed to reach this goal five years ahead of target. Globally Coca-Cola works in over 2000 communities and supports more than 248 community water partnership projects in over 71 countries – this being one of them.
We are delighted to announce that the South East Rivers Trust is delivering one of these three projects which will see a large (and I mean very large) silt trap, known as a Downstream Defender® supplied by Hydro International, installed onto a surface water drain. The drain currently carries run-off from the incredibly urban surrounding catchment directly into the Beverley Brook. The Downstream Defender will trap a large portion of the sediment and associated contaminants, preventing them from reaching the Beverley Brook. Intermittently the trap will be emptied with a gulley sucker and the toxic sludge removed to landfill. Consequently, the health of the river will improve making it a better place for both wildlife and people.
Last Tuesday we launched this collaborative project with the arrival of the Downstream Defender to Richmond Park. We’d like to thank our funders, the Coca-Cola Foundation, as well as all our partners including WWF, The Rivers Trust, the Environment Agency, The Royal Parks, the Friends of Richmond Park and Thames Water. Also a big thank you to Hydro International for supplying the Downstream Defender and for their much appreciated contributions to the launch event. Thank you to all the guys at Kenward Groundworks; Tony, Matt, Dave, Mark and Woody for all your efforts with installing the chamber. And finally thanks to John Sutton from Clearwater Photography for taking photograph of the launch and project.
Partners with the Downstream Defender Silt Trap
Celebrating the launch of the project with partners and volunteers
Photos: John Sutton, Clearwater Photography