Greening Brownfields

Greening Brownfields: Unlocking the potential for SuDS on brownfield land

This International Women’s Day we are celebrating the inspirational women that contribute to our success. Leading the way are the heads of our Water and Geoenvironmental teams, Jacqueline Diaz-Nieto and Amy Juden, who share their collaborative thoughts on the potential for SuDS to be used on brownfield sites.

With a housing crisis that shows no sign of slowing, coupled with a desire to conserve our dwindling green spaces, there is a renewed push to find development space on brownfield land. The regulative landscape will soon see the introduction of Schedule 3 which means the industry will need to consider using sustainable drainage systems (SuDS) on every development site.

Using sustainable drainage systems on brownfield land brings advantages. Sustainable drainage systems can be designed to complement the ground conditions and constraints and bring multiple additional benefits to a project; greening brownfield sites. The wide-ranging positives of this approach shouldn’t be underestimated.

Schedule 3 requires designers to consider SuDS within a hierarchy that prioritises discharging surface water to ground, and with SuDS also serving a dual purpose of satisfying the Biodiversity Net Gain (BNG) requirements, making SuDS work on brownfield sites makes financial and environmental sense and will ensure compliance with new requirements.

Resistance may exist against infiltration drainage on potentially contaminated sites. It is true that infiltrating water has the potential to mobilise soil contaminants and subsequently pollute rivers and groundwater, however, depending on the contaminants and their leachability (mobility in water), infiltration could be acceptable if properly assessed and designed. This is especially true for diffuse infiltration limited to pre-development rates, which is likely to be suitable on all but the most severely contaminated development sites. Concentrated soak-away drainage might not be suitable through made ground or contaminated materials, but it may still be possible to locate these to discharge at slightly greater depth into natural ground, or on a less contaminated part of the site. Even on development sites where leachable contamination has been identified it may be possible to plan the remediation strategy such that these soils are relocated to less sensitive areas or capped by hard surfacing.

Even on highly contaminated sites, SuDS designed not to infiltrate can bring significant advantages, and shouldn’t be ruled out. Waste disposal costs for contaminated soil, particularly if classed as hazardous can be a significant cost to development. Keeping drainage systems shallow and designing out deep drainage and large attenuation tanks can reduce the associated excavation and removal costs, particularly relevant for contaminated ground. Shallow water storage used in SuDS could include gravel layers or geocellular crates under permeable paving or lined landscaping features. These solutions can come into their own for redevelopment of former landfill sites, where not only is excavation and soil disposal costly, it may also come with specific environmental permitting requirements. With wait times for some bespoke environmental permit decisions extending over 24 months, this is not an appealing option for developers or contractors, and SuDS may provide the solution!

SuDS champions often talk about the four pillars of good SuDS being the design for quantity, quality, amenity and biodiversity. Whilst often overlooked by traditional drainage designers, the potential amenity and biodiversity benefits of SuDS on brownfield land is huge and can strengthen the case for making SuDS work on brownfield land. Well-designed SuDS not only provide the hydraulic attenuation requirements to achieve greenfield runoff rates, reducing the risk of flooding downstream, but vegetated SuDS (with the shallow attenuation below ground) provide much-desired urban greening, they also bring a myriad of other social and environmental benefits.

SuDS sells! SuDS provide multiple landscape and biodiversity benefits, making new developments an attractive place to be as well as providing amenity and social value along with the economic advantages of rejuvenating an area. Together these factors make developments much more desirable. This is particularly pertinent when a site was previously derelict, unused, or unloved. Getting SuDS onto your brownfield sites is literally turning brown to green!

Success in these designs depends on understanding the ground model, specific constraints in the ground from previous uses, levels of contamination and the pathways for contaminant migration. Drainage designs for brownfield sites therefore benefit massively from the input of geoenvironmental professionals from the start. Experts who understand all aspects and can advise SuDS designers on safe working depths for the SuDS attenuation layer and specify from the start whether leaky SuDS can be designed, busting the popular myth that SuDS on brownfield sites must be tanked.

At EPG, our combined skills and experience in drainage design, ground conditions and land contamination allows us to unlock the potential benefits of SuDS on brownfield sites and provide clients with a one-stop shop.

Our dynamic team is changing the narrative around holistic environmental designs for challenging sites. Don’t believe anyone who tells you that you can’t infiltrate on brownfield land. Challenge any design that includes a deep-dig through contaminated ground for a large attenuation tank. Get in touch with EPG to see if we can do better and provide you with a more cost-effective, greener design using our innovative approach.