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Harnessing the benefits of Sustainable Drainage Systems (SuDS)
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In recent blogs, we introduced the concepts of Biodiversity Net Gain (BNG) and Natural Capital (NC) as important tools in enabling balanced decision-making for sustainable development. Continuing our green infrastructure series, we explain the role that Sustainable Drainage Systems (SuDS) play in achieving BNG and NC, and their increasingly important use in combating climate change through sustainable development.

So what are SuDS?

SuDS are primarily a method of managing rainfall within the built environment. Traditionally, drainage systems routed rainfall to underground pipe networks, aiming to drain the site to sewer as rapidly as possible. Depending on the age of the system, the sewers either led directly to watercourses, contributing to increased flood risk downstream, or to sewage treatment works, contributing to the occurrence of combined sewer overflows (CSOs), in turn impacting the water environment, as recently reported in the UK media.

To combat these adverse outcomes, SuDS instead aim to mimic the natural environment’s response to rainfall, usually by incorporating natural elements at the ground surface which reduce the flow of water offsite, as currently being implemented at the former British Army training camp at Whitehill Bordon, Hampshire’s emerging Green Town. Examples of SuDS include green roofs, ponds, basins, swales, wetlands and rain gardens.

The need for sustainable drainage is not new. SuDS first appeared in the late 1990s and have since been progressively adopted and developed in many countries across the world. Improving river water quality by reducing sewer discharges has been a major focus in the US for over 30 years. SuDS are also being implemented across Europe, with case studies in major cities such as Barcelona leading the way in Spain, where a technical guide for SuDS (in Catalan) has recently been released to provide a framework to increase implementation.

Why SuDS matter

My own experience of SuDS began in the mid-2000s, as a means to manage flood risk downstream of new developments. Indeed, flood risk assessments (FRAs) remain the primary driver for the implementation of SuDS in the UK, driven by the requirements of ‘lead local flood authorities’ (LLFAs) in their role as statutory consultees for drainage. However, alongside their core functions of managing the flow and quality of water, it is now recognised that well-designed SuDS can mimic the natural environment’s ability to provide additional benefits to society and the environment. Their ability to recharge groundwater resources, provide habitat for wildlife and deliver attractive and healthy places for people align perfectly with the concepts of biodiversity net gain and natural capital.

Resilience to climate change and reversing the degradation of our natural environment are challenges that will increase in importance over the coming years. Regulation and oversight frameworks will continue to be strengthened in response, such as the upcoming updates to industry-endorsed SuDS guidance in the UK, which is expected to significantly strengthen the ability of the LLFAs to drive the delivery of multiple-benefit SuDS through the planning process for new developments. A holistic approach to SuDS design will therefore be essential to successful delivery of these increasingly integrated solutions.

An innovative, integrated approach

In the UK, the biodiversity aspects of the Environment Act 2021 show the benefits of an integrated approach, such as the target to halt species decline by 2030 by (amongst other things) requiring new developments to deliver a 10% increase in biodiversity. SuDS can contribute considerably to BNG requirements through water-enriched habitat. Wetland habitats are often valued highly in a BNG context, potentially enabling BNG to be achieved in a smaller area, and increasing the potential for all biodiversity gain to be delivered on site. This provides cost-efficiencies for developments that achieve an integrated approach, and has the added benefit of bringing nature closer to communities, increasing the natural capital value of the development.

Over the last 20 years at Wood, we have seen the market drivers grow from designing and delivering SuDS in response to flood risk assessment of new development, to providing a truly integrated solution to our clients, in line with an increasingly integrated regulatory environment. Our extensive experience in flood risk management helps maximise opportunities for SuDS, supported by our industry-leading augmented reality FloodVue™ tool, which offers the ability to visualise potential flooding scenarios through a clear, immersive picture of severe weather impacts at any location globally.

Alongside such innovations, strategic and development-led masterplanning can maximise value by integrating SuDS early in the design process, realising their benefits across a range of projects. By co-locating SuDS with other development constraints and opportunities, we can minimise unnecessary land-take and achieve integration of blue-green infrastructure, amenity and landscape, biodiversity and urban design, ensuring developers are well-placed to respond to the challenges posed by climate change through sustainable and environmentally-sensitive projects.

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