LANDSCAPING & EXTERNAL WORKS 67
A SUSTAINABLE MIX OF GREY, GREEN & BLUE
As the UK targets 1.5 million new homes, sustainable drainage must be part of the plan, says Ben Puddy of Hydro International; he explains how blending blue, green and grey systems can build the perfect drainage mixture to support climate-resilient communities.
T
he Government has put housing at the heart of unlocking growth in the UK, committing to deliver the biggest housebuilding programme in two generations.
The deliverability of building 1.5 million homes, the overhaul of the UK’s planning system, and the impact on the green belt have so far dominated the debate.
What receives considerably less airtime is climate resilience: the question of how, in a time when extreme weather events are becoming commonplace, we can deliver new settlements and towns with the drainage systems that are suitable for a changing climate.
BLENDING NATURE & ENGINEERED SOLUTIONS With targets in place for Biodiversity Net Gain (BNG) and a greater focus in the development community on creating green and biodiverse spaces that promote community wellbeing, there is a drive to embed nature-based drainage solutions. Green and blue – nature-based solutions on the surface – are increasingly being seen as the prime solution to alleviate the burden on our wastewater infrastructure. The reality is that on many sites it is often more effi cient for these solutions to be integrated with below ground ‘grey’ systems.
There are a number of reasons why this blend of drainage engineering is likely to be more successful. For many new housing sites, a solely natural green and blue SuDS solution that returns surface water into the environment is often not feasible due to limitations including soil types and ground conditions. n these scenarios, grey ow
attenuation systems are vital to effectively manage surface water runoff. Selecting the right ow control solution
is an essential element of a successful SuDS system. A better performing ow control passes a higher volume of ows earlier during rainfall and means that less capacity on site is needed to store excess ows. This approach not only reduces the land take of storage ponds or detention basins where needed, but also cuts construction costs.
SuDS installations must be resilient to increased run-off from urban creep, new developments and a changing climate. Flow controls that have the option for future adjustment will be key, as changes in ow rate can be accommodated through modifi cations to the unit, rather than requiring total replacement. Blended grey, green and blue solutions can make best use of the land available and provide housebuilders and developers with an optimal combination of effective surface water storage and public amenity space. Sitting beneath swales, detention basins or ponds, storage and infi ltration tanks add capacity while
reducing the surface-level impact of the drainage solution. Adding smart ow and sediment level monitoring within these below ground stormwater drainage systems provides asset owners with a greater understanding of performance over time. This enables proactive maintenance and optimises environmental protection.
THE GREY ADVANTAGE Ponds and swales have the ability to treat water suffi ciently to meet water quality legislation (as outlined in the CIRIA SuDS Manual (C753) Simple Index Approach). However, an additional proprietary, below-ground grey solution can boost performance and bring additional benefi ts.
A stormwater treatment system, incorporated upstream of a pond can provide effi cient pre-treatment and remove sediments, litter and hydrocarbons while reducing the footprint of the wider solution.
NATURE-BASED AND GREY UNDERGROUND SYSTEMS ARE NOT AN ‘EITHER OR’ DECISION FOR HOUSEBUILDERS
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