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With the new Government’s focus on housebuilding and infrastructure, it is worth remembering that the Plan for Water, and the anticipated introduction of Schedule 3 of the Flood and Water Management Act 2010 in England suggest that SuDS designs must comply with new legislation to deal with both water quantity and quality. With the current emphasis primarily on stormwater quantity, developers, engineers, installers and asset owners may be less knowledgeable about water quality, and the treatment methods available to reduce the risk of pollution.
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SuDS Best Practice focuses on managing rainfall where it lands and using vegetative/green infrastructure, rather than below-ground engineering (grey infrastructure). A major source of water pollution is surface water runoff from built-up areas and highways. In fact, polluted surface water contributes to 18% of water bodies failing to reach ‘good’ status in the Water Framework Directive.
Where the pollutant loads from the runoff has been underestimated, or the vegetative SuDS inadequately configured or poorly maintained, the system may be unable to effectively capture, retain and treat the pollutants. Biodiversity is another element of SuDS Best Practice. A SuDS pond, if used as the “first defence” for medium to high pollutant loading, can itself become a poisonous environment for the very wildlife it is designed to attract, as well as increasing the risk of mobilising pollutants during cleaning, leading to polluted discharges entering downstream water bodies.
Proprietary grey infrastructure treatment devices, placed upstream of vegetative SuDS, can provide a “first defence” to incoming pollutants and protect green infrastructure. Designers of SuDS systems need to better understand how grey infrastructure can be deployed to target specific pollutants before they reach a vegetative SuDS element. This combined use of grey and green can lead to optimised designs that provide best hydraulic and water quality performance, together with lowest cost and environmental impact.
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