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SuDS: the hard and soft side of climate resilience

23 May 2019

SuDS can either be natural or engineered. Here, Martin Lambley, Product Manager at Wavin UK, takes a look at the advantages and disadvantages of both options.

SuDS: the hard and soft side of climate resilience
Image credit: Susdrain

When you talk about Sustainable Drainage Systems (SuDS), it can mean different things to different people.

SuDS generally aim to mimic natural drainage, but for some this means using man-made or engineered structures, and for others it's about natural landscape features.

In this post, we take a look at the pros and cons of both and how they can be utilised to help provide optimum resilience to climate change and the extreme weather that's associated with it.

Generally SuDS follow the principles of natural drainage, managing surface water as near to source of possible and using a variety of methods to slow the flow, attenuate and infiltrate.

Landscaped SuDS include ponds, basins and swales, but there's also a ‘grey’ infrastructure approach which utilises hard or engineered components to ensure optimal capacity for high rainfall.

So, which is likely to provide the best solution to climate change and the extreme weather conditions associated with it?

Landscaped SuDS

Landscaped SuDS include features such as attenuation ponds, rills and swales that are integrated into the landscape and collect water during periods of high rainfall before letting it slowly soak into the ground.

Planting with hardy and drought-resistant vegetation can be used to slow flow and naturally cleanse water. The natural features of landscaped SuDS are also ideal for boosting biodiversity and creating better places to live with attractive open areas and increased amenities.

The well-being value of SuDS is well-recognised and includes increased opportunities for physical activity, improved air quality, space for relaxation in order to reduce stress and improve mental well-being. All of these benefits are especially true when the features form an integral part of the overall landscape design.

While landscaped SuDS have many benefits, the downside is that they can take up significant areas of land, making them unsuitable for some sites. Cost is a big implication for developers when allocating large areas of land to such features.

Maintenance and adoption issues of landscaped SuDS have also, in the past, prevented them from being implemented in some situations. While landscaped SuDS that are integrated into the overall landscape design appear to be the ultimate answer to our climate change issues, in many situations, a more pragmatic approach is required.

Engineered SuDS

Engineered SuDS include permeable paving, geocellular attenuation and infiltration tanks and are ideal for high density, commercial and industrial developments.

Geocellular tanks are commonly used to manage surface water runoff either as a soakaway or storage tank. They are usually modular and flexible, robust and easy to install.

The key benefit with them is the large volume of water that can be stored in a relatively small site. They're often also perceived as lower risk than landscaped SuDS, as capacity and flow rates can be guaranteed allowing for accurate modelling of different situations by engineers.

Geocellular tanks are often employed as a solution with proven qualities and performance to reinforce and enhance planning applications therefore enabling planning developments to proceed.

Engineered SuDS can be engineered to help manage water quality but do little to address the requirement for SuDS to provide of biodiversity and amenity, however they're suitable for use underneath public spaces such as play areas and therefore allow optimal use to be made of the space available.

Engineered SuDS tend to offer a more predictable and lower risk maintenance plan that, in the past, water companies have been more willing to adopt. Some of the issues around the adoption of SuDS could be set to change with the upcoming Sewers for Adoption 8th edition guidance.

A combined approach

A greater understanding of the SuDS solutions available will allow engineers and landscape architects to use a combined approach to surface water management on any given site that blends both engineered and landscaped SuDS, allowing each to play to its strengths and providing the optimal range of benefits for all stakeholders while ensuring optimal resilience to climate change.

There isn’t necessarily a single correct answer to SuDS design to help increase climate resilience but there may be several options that can be used depending on the design criteria and opportunities and constraints of the site.

Landscaped SuDS can often be used for source control, which manages rainfall where it falls, while engineered SuDS will provide a more robust and high capacity option for storage of rainfall.

For example a green roof utilises a vegetation layer grown in a substrate with a drainage layer below to promote storage, attenuation and evapotranspiration, meanwhile providing benefits like thermal comfort and biodiversity.

For extreme weather events in urban areas, where there may not be space available to achieve the required conveyance capacity through landscaped SuDS alone, and the addition of hard SuDS is essential.

The upcoming sewers for adoption 8th Edition guidance will allow a route for adoption of some landscaped and engineered SuDS. It will allow for them to be properly considered and integrated into the urban design process and provide schemes that meet surface water management requirements and improve climate resilience, while also contributing a range of other benefits, including increased air quality, improved mental well-being and increased biodiversity.

What do you think? Could a combination of engineered and landscaped SuDS be a way of making our urban areas more resilient to climate change?

Sign up to Wavin’s Spotlight, an initiative to promote ‘out of the box’ thinking around the challenges posed by flood waters, climate change and urban development.

Want to learn more about SuDS

Visit the ICE and Wavin Sustainable Drainage Systems Hub and discover more cost-effective and sustainable ways to manage the rise of excess surface water.

  • Martin Lambley, global urban climate resilience product manager at Wavin