Despite being a legal consideration for almost a decade, the deployment of effective sustainable drainage systems (SuDS) has, to date, been far too slow – often treated as an afterthought of any new build. However, evolving legislation, climate change and the social pressure to prioritise green spaces are all making the use of SuDS more critical than ever before.

17.12.2019
 
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Here, Paul Wagstaff, Head of Product Management at Aggregate Industries UK, looks at how integrating drainage design at the very start of the feasibility stage of every project is the key to speeding up the SuDS revolution.

While the British weather has always been difficult to predict, recent years have seen a distinctive shift towards even more erratic weather patterns. We only need to look at the persistent wet weather this autumn to see this, as an ongoing deluge of torrential rain throughout October and November have resulted in widespread flash flooding across many parts of the UK, causing devastation and chaos in its wake.

Sadly, amid the ongoing climate crisis, the flood threat is set to increase – those were the were the words of the Environment Agency's (EA) Director of Flood Risk Management, John Curtis, who recently admitted that the flooding is likely to get much worse, happen more frequently and more often.

Currently, around 5 million people live in flood risk areas in England and Wales. However, with an estimated average global temperature rise of 4°C (far above the target of 1.5°C set in the legally binding 2015 Paris Agreement) by the 2080s, many at-risk UK towns may have to be abandoned altogether – that is, unless tangible action is taken now.

Yet, surprisingly, despite the very stark risk presented by flooding, the mitigation efforts around it have, thus far, been somewhat limited. Although the government passed a new law requiring all new developments to include sustainable drainage systems (SuDS) in 2010, it quickly put the rules on hold in a bid to help developers to keep costs down and speed up house-building rates.

Consequently, flood defence measures have been typically overlooked in the building planning process, often being left as an afterthought in the final design stages, forgotten entirely or fitted  retrospectively after a flood has happened. 

Further exacerbating the issue is the rapid rate of urbanisation. Increased infrastructure means an increase in impermeable surfaces – and thus less opportunity for natural ways of excess water being diverted into the drainage network to local watercourses. Given the strain already put on the UK’s old drainage system, which was not built to cope with current volumes, in some cases this has resulted in sewer and surface water flooding.

So, what’s to be done if we are to help safeguard the UK from a large scale flood crisis? 
While not a new concept, a good and often underutilised starting point lies with a SuDS strategy. In short, SuDS is a multi-layered drainage system designed to manage surface water runoff, in a bid to decrease flow rates to watercourses and improve water quality, in a more sustainable and effective way than by conventional drainage such as pipes and tanks.

A typical SuDS will use a combination of water practices to form a holistic management system. This could include source control methods designed to decrease the volume entering the watercourses, such as a green roof comprising of vegetation and landscape designed to intercept and retain precipitation, and pre-treatment steps, such as vegetated ditches helping to remove pollutants. This may be supported with retention ponds, providing storage and treatment for excess water, and infiltration systems, such as trenches and soakaways.

But the considerations don’t end there. In order to fully maximise a SuDS potential, it should be supported with the use of permeable surface material options. This could be, for example, a fast-draining concrete paving solution designed specifically to direct excess water off streets, parking surfaces and driveways, or a porous asphalt blend which will aid water flow measures in vehicle trafficked areas. Here the remit is to allow water to pass through the material into the underlying permeable sub-base thereby maximise control measures.

Of course, this approach does require investment; but it can deliver benefits on multiple fronts. When formalised as an integral part of the design process, good SuDS can significantly help control run off and reduce peak flows, therefore reducing the risk of flooding while also improving the water quality with the removal of pollutants. Plus, in terms of sustainability, SuDS design can create new habitats and rehabilitate or enhance existing ones – benefiting the landscape, community and helping developers tick the ‘green box.’

As we look to the future, the only way to tackle the current housing deficit will be to build more, but with flood incidents only set to increase, it will become ever more important for preventative measures to be incorporated into the inaugural development stages.  Furthermore, with the government currently working on the latest draft of its Flood and Coastal Erosion Risk Management Strategy and flood-risk becoming an even more prominent consideration for would-be house buyers, the issue isn’t going to go away. For that reason it is time for housebuilders to invest in good SuDS en masse and protect homeowners from flooding.

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