Thursday, 28 January 2021 17:55

Can SuDS help achieve biodiversity net gain?

By Mark Manning, Business Development Manager, SDS

Floods, droughts and wildfires provide us with frequent reminders of the impacts of global warming, but the catastrophic decline of wildlife species familiar to our grandparents, from skylarks to house sparrows, frogs, toads, butterflies, moths, barn owls, bats and wildflowers is a silent, almost unnoticed emergency.

sds GEOlight web copyMore than 100 British species have become extinct in the past 100 years and many more are threatened. Some, like bees, are the very lifeblood of nature's health and well-being.

Multiple Benefits
Could Sustainable Drainage Systems (SuDS) help to redress the balance and stop biodiversity declines? The potential of SuDS to green urban infrastructure and encourage wildlife has certainly long been recognised as one of the four 'pillars' of SuDS, alongside their ability to protect against flooding, treat pollution and provide community amenities. Now, the Environment Bill, currently progressing through parliament, embodies a requirement for new developments to deliver a 'net gain' in biodiversity, and SuDS could help developers to achieve those obligations.

Indeed, the Government, in its 25 Year Environment Plan, and in the Environment Bill, has set out a vision for SuDS to be part of a more comprehensive drainage approach to reduce flooding and deliver other benefits, which it says will be clarified in forthcoming revisions to Planning Practice Guidance. This will include how using SuDS can contribute to the delivery of biodiversity net gain. Under the new Environment Bill measures, applicable new developments must deliver a 10% net gain in biodiversity, using a mitigation hierarchy and metric system.

sds Berewood Courtesy of Grainger PLC web captioned copySo, what is Biodiversity Net Gain? Biodiversity net gain is an approach that mandates the need for a development to end up in a better position to support wildlife and habitats than it was before construction began. For some developers, net gain may seem like more red tape and planning hurdles curtailing their profitability, not to mention their freedom to deliver on the Government's equally forceful expectations for new homes and infrastructure.

How Can SuDS Make a Contribution? Bringing drainage to the surface with ponds, swales and basins, offers a dual-purpose opportunity for developers that could limit the commercial loss of land to usable development especially in space-restricted urban sites. So, biodiversity net gain makes the aspirations for SuDS more deliverable, and SuDS can help to support healthy habitats.

Best-Practice Designs
SuDS present an opportunity to use vegetative, landscaped features to manage surface water on a site. They can be designed entirely above-ground, or used in combination with manufactured products, for example, underground stormwater attenuation tanks, such as SDS's GEOlight modular storage system and treatment devices such SDS's Aqua-Swirl vortex separator. Best practice SuDS designs mimic natural processes and manage rainwater as close as possible to where it falls, often by attenuation or infiltration.

However, net gain should also force developers to take a mature approach to good SuDS design. Drainage designers and their developer clients must be guided to understand the needs of the local flora and fauna and consider the whole ecosystem, and to deliver connectivity between habitats both on and off the development.

sds Integrating green infrastructure web copyDesigners should also consider carefully the role of vegetative SuDS components in providing pollution control. If ponds and wetlands are deployed as sacrificial devices to treat pollution, then their ability to support wildlife could well be compromised. Using a hydrodynamic vortex separator, such as SDS Aqua-SwirlTM, at the inlet to the pond to remove sediment and pollutants in the runoff is highly advisable, so that the stormwater management system works in harmony with the environment. Designing a 'hybrid' SuDS system and combining a basin, pond or swale with a manufactured device provides assurance of measured, repeatable and effective pollutant removal.

We should also never forget that water reuse is the first priority of the SuDS design hierarchy, yet this is all too often overlooked. Capturing surface water for reuse by means of rainwater harvesting systems is a legitimate sustainable drainage function, that also saves water in drought prone and water scarce areas. If saving water is a priority, then the biodiversity benefits may be better delivered appropriately, elsewhere. Captured rainwater could even be reused to water the habitats we create, helping the flora and fauna to thrive.

Best of Both Worlds
In our enthusiasm to deliver biodiversity, adapt to climate change and develop more homes and better infrastructure, conflicts of interest can emerge, where one aim is in danger of thwarting another. Sustainable Drainage Systems can help developers to achieve the best of both worlds. Used appropriately alongside other stormwater management or smart technologies, they can help deliver holistic designs that truly connect and restore biodiversity.

What happens next? The Environment Bill is currently progressing through Parliament. Once the Bill receives royal assent, a two-year transition period is planned before a mandatory, audited system of biodiversity net gain becomes law as part of the English planning system.