One of many reasons why the take-up of Sustainable Drainage (SUDS) has been less than enthusiastic in England and Wales is the lack of long-term monitoring of SUDS devices and the perception that SUDS don’t work.
The SUDS Applied Research Group at Coventry University has been working with practitioners to provide such data by monitoring the efficiency of SUDS devices such as porous paving systems (PPS), rainfall harvesting installations and vegetated surfaces.
Tarmac Ltd. is a West Midlands firm based in Wolverhampton famous for its road surfaces, but it also makes a PPS called Aquifa™. Members of the SUDS Applied Research Group have been adding contaminants (oil and Coventry street dust) to models of various PPS including Aquifa™, then artificially raining on them to determine how they deal with the pollutants:
Fig 1: Porous paving system surface with patches of contaminant
It was found that very little of any of the contaminant appeared in the effluent water after eight months of monitoring. This work is on-going with a further 18 months work in the planning stages.
Fig 2: Heavy metal concentrations in effluent from a Tarmac Aquifa™ porous pavement after 8 months contaminant additions.
Work in collaboration with the Sport Turf Research Institute and vegetated PPS manufacturer Atlantis, has assessed the ability of various grass species to tolerate oil contamination (Fig 3).
Fig 3: Growth of ryegrass at 0%, 5% and 20% oil contamination
The study expanded to determine the distribution of metals and oil in a vegetated PPS at a primary school in Kenilworth, Warwickshire (Fig 4).
Fig 4: A 5-bay vegetated car park at Clinton Primary School, Kenilworth, Warks
Work is still on-going, with the distribution of metals and oil in the car park bays being plotted onto a geographical information system to allow for the comparison of their concentrations with grass wear and lack of growth.
As was found out during the summer of 2006 and particularly 2007, hard engineered approaches can now no longer cope with excess surface water runoff, with the result that many people have endured the misery of a home flooded with water, or worse.
If predictions of climate change are to be believed, intense storms will become the norm in Britain and SUDS seems set to become one of a powerful arsenal of techniques the Government are supporting to mitigate these impacts.
If manufacturers such as Tarmac Ltd. carry out monitoring and have the data to show the efficiency of their product, then they will be at a distinct advantage in the PPS marketplace and SUDS will be taken as seriously in England and Wales as it is currently in Scotland, USA and Scandinavia.