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Blue / green infrastructure in urban regeneration

Sustainability By Bill Wilkins, Associate Director, Civil Engineering – 04 November 2021

Overhead view of the Water Garden Project, a series of rectangular water beds in between multi-storey buildings


Bill Wilkins smiling in a striped shirt and dark suit in front of a brick wall

Bill Wilkins

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With COP26 here, the clamour for delivering net zero carbon (NZC) has never been greater. Everyone is focussed on understanding net zero carbon and developing their strategies to address this as we speak, and quite rightly so.

However, most of the focus with these discussions and actions plans tend to be around the building fabric and how we can operate the buildings more sustainably. This is perfectly understandable as currently the operational carbon interventions are better understood and more easily quantifiable compared to embodied carbon in an infrastructure environment. Embodied carbon by comparison is still in its infancy in terms of our quantifiable understanding of the benefits that can be gained through good sustainable design.

Notwithstanding this, as engineers we believe we have a good understanding qualitatively of the right choices from a NZC perspective while we all continue to develop our carbon accounting tools to address this side by side with living lab data gathering studies that are ongoing.

I think it is also fair to say that we will never achieve net zero carbon when focussing on the embodied carbon within external infrastructure alone. However, without a comparable focus on reducing embodied carbon in external spaces / infrastructure construction materials we will not achieve the Paris agreement targeted climate-change mitigation (in terms of greenhouse gas emissions - GHGs - and limiting the global mean temperature rise to 1.5°C ) we are hoping for.

In fact, if we carry on as we are, experts predict that temperatures will rise by at least 3.2°C by 2100. We have seen what impact the current global mean temperatures have had on the environment by rising 1.1°C above pre-industrial levels. We are experiencing increased flash flooding, rising sea levels and melting icecaps, increased heat waves and forest fires - all having a devastating effect on our biodiverse habitats. Some of these events were not predicted to be experienced until we reached 2°C of global warming, so you can see why so many are fighting for immediate action rather than more “blah blah blah” as Greta Thunberg would put it (her comments perfectly justifiable by the way!).

So, as a Chartered Civil Engineer and somebody who has been passionate for some time about sustainable placemaking being embedded into all of our external schemes, I feel it is our duty to re-emphasise the importance of implementing blue and green infrastructure (BGI) on all schemes as part of our suite of tools we must use to help address this climate emergency.

What is BGI?
I won't go into great detail here about what BGI is or where we have previously used it effectively; for more information, please refer to our Blue-Green Infrastructure thought leadership webinar.

When designed correctly, BGI can help not just with mitigating embodied carbon (when delivered as natural solutions working in synergy with landscaped urban greening and/or integrated water management strategies) but also help to make our developments far more climate resilient, especially when it comes to flood mitigation.

Implementation of good BGI brings with it the additional benefits not just of carbon reduction and flood mitigation but also biodiversity net gain, urban heat island effect mitigation, air quality improvements and amenity / social value.

Studies have also linked BGI with an increase in productivity, land values, local spending and a reduction in crime levels. All of these benefits sometimes extend well beyond the red line boundary.

I think we can also all agree that over the duration of the pandemic the importance of green space and connecting with nature on the health and wellbeing of us as individuals has been identified and gained increased recognition exponentially.

What are the drivers?
So, you would think it was a no-brainer that the implementation of nature-based BGI solutions should be a fundamental part of any sustainable development?

Unfortunately, as many of us will have experienced, there has in the past been a perception that BGI was just greenwashing with little payback on investment to justify the "additional" outlay, with the inevitable value engineering exercise putting paid to the good intent of earlier design stages in lieu of the cheaper grey infrastructure with sustainable urban drainage systems (SuDS) tanks in the ground to remain compliant with National Planning Policy Framework requirements and flood legislation.

This "downgrading" wasn't helped by the fact that there wasn't much by way of legislative powers at a national level with sufficient teeth to enforce delivery. Much of the governance devolved to a local planning level generally with enough wiggle room to avoid mandatory nature-based SuDS solutions incorporation working symbiotically with rain gardens, tree canopies with tree pit soakaways, swales and attenuation ponds (ecological infrastructure if you like).

Fortunately, our understanding of the climate emergency has increased almost concurrently with an appreciation of the importance of green space for both our physical health and mental wellbeing. We are now seeing this in our cities especially, where the social and economic impact of the pandemic has raised fundamental questions on how our cities need to change and regenerate to react to the new "norm". We have seen some public and private sectors undergo five normal years of change in less than 18 months amid a huge acceleration in trends such as remote working and the shift to online retail.

These changes have not been driven by legislation changes, although the government's 25-year environment plan - the Environment Bill - is looking to mandate biodiversity net gain and local natural recovery strategies when it eventually becomes law potentially in 2023. These changes were directed by the market in terms of:

  • financial institutions insisting that they will only invest in businesses and developments with NZC pathways / targets
  • portfolio owners look to demonstrate their assets are ‘Paris Proof’ utilising methodologies such as the Carbon Risk Real Estate Monitor (CRREM) and Task Force on Climate- Related Financial Disclosures (TCFD)
  • more astute occupiers demanding more sustainable placemaking from the buildings and surrounding external spaces that they are looking to lease and are willing to pay a premium for such space

Such schemes are also capable of winning investment from government funds such as the Levelling Up Fund, Community Renewal Fund and Towns Fund which will help with the delivery of these interventions without the need to value engineer down to the bare minimum needed to remain compliant with current legislation and planning policy.


So, we have the improved knowledge, the technical means and the public will to incorporate BGI into all of our new and retrofitted developments.

By using nature based BGI solutions, we can start to address the climate emergencies simultaneously with delivering better-quality places for people and nature. Equally, if designed correctly to work symbiotically with landscaped urban greening as one solution rather than two, it can be delivered economically with very little increase in cost compared to more traditional external works finishes and underground SuDS solutions.

The multifunctionality of BGI (or ecological) infrastructure is the key to maximising the benefits here and departing from the “simply greenwashing” mindset that has in the past led to its demise at cost plan stage.

But of course, BGI alone will not solve all of our greenhouse gas emissions or NZC targets. For that, we need a suite of technological and nature-based solutions as well as behaviour changes. However, it is now an important part of our overall embodied carbon reduction and climate resilience strategies, and more importantly we now have the will of investors and end users alike to incorporate into all our schemes.

It is this public determination, more than the slightly toothless legislation currently in play, that I hope and believe will encourage higher-quality sustainable placemaking developments and workspaces to become the "norm" far sooner than any national or local net zero carbon targets will enforce. It will be interesting to see if, amongst other things, the delegates at COP26 from 31 October get into enough detail to give any consideration to the treatment of our external spaces and the strategy to achieve this urgently (as the market is now doing) rather than just more long-term “blah blah blah” targets. I may be listening as I eat my lunch in Angel Meadow or Cathedral Gardens.