Blue-green thinking

With the country bracing itself for yet another winter of storms and heavy flooding, Luke Strickland of Ramboll Environ looks at the options available to local authorities. 

It's a sad state of affairs that the flooding of our communities and cities has become 'business as usual' and it highlights the growing disconnect between our built environment and the natural environment. I'm sure many of us would agree that we need to adapt our infrastructure to accommodate a changing climate and this includes making space for water in the right places, rather than in the living rooms of people's houses and the ground floors of their businesses. With more and more responsibility being placed on local authorities in terms of practically managing flood risks on a local scale, what options do they have?

The recent National Flood Resilience Review called for more investment in temporary and permanent flood defences over the next 10 years and Theresa May has even placed three battalions of troops on standby to assist in the defence and clean-up from flooding this winter. It's promising that flooding is high up on the Government agenda but, as effective as hard flood defences can be, even the newest ones can be breached - there's always a bigger storm around the corner. Further, they often detract from the public realm and distance people from the natural environment. Sadly, central government spending only goes so far and it can be a lottery as to where the Environment Agency receives funding to build or improve flood infrastructure.

An approach that has been gaining visibility in recent years is natural flood management or "blue-green infrastructure". Natural flood management encompasses a portfolio of approaches and techniques to store and slow rainwater. Examples include trees, "leaky" dams, wetlands, swales and greened roads and public spaces. In this sense, it's nothing particularly new, and on its smaller scale it overlaps with the softer elements of Sustainable Drainage Systems (SuDS). Rather than providing a sole "big ticket" solution to flooding (such as hard flood defences), it's all about a portfolio of smaller interventions providing marginal gains that accumulate through the catchment. 

Image

For too long, the answer to flooding has been resistance: keep it out. Increasingly, the rhetoric is about resilience instead; a recognition that we can't hold the waves at bay. The Chancellor's Autumn Statement, for instance, promised funding to improve the flood resilience of the national road and rail infrastructure.

Natural flood management approaches and blue-green infrastructure provide the multiple benefits we need from a resilient and effective public realm. As well as conveyance and attenuation of flood water, they can provide amenity, attractive spaces and habitat, therefore making a big contribution to improving our collective health, as well as helping our citizens reconnect with the natural environment. The challenge is how to normalise this approach into new development and retrofit it with our existing public realm.

The city of Copenhagen is an excellent case study. On 2 July 2011, 150mm of rainfall fell in just two hours, leaving swathes of the city under up to a metre of water. The city described this as a "cloudburst" event, from the old Danish word skybrud, and it seems a fitting term for the intense storms that are becoming more frequent across Europe. Insurance claims from this flood exceeded over €800m.

Since then, city planners in Copenhagen have been actively seeking to understand how the city can become more resilient to flooding and at the same time increase amenity, ecology and liveability. They developed an overarching cloudburst strategy for implementing resilience, which cascaded into detailed catchment plans. The first adaptation projects have now been completed, with many more still in development.

These solutions take the form of a portfolio approach towards public realm improvements, including cloudburst streets for rainwater retention and conveyance, green streets and central areas of retention in existing squares and lakes. Road profiles and cambers are adapted to provide surface level water storage in cross-section, whilst also keeping a dry lane to maintain movement across the city. 

While it's not a silver bullet, natural flood management through blue-green infrastructure is both feasible and deliverable, and in the face of a changing climate, perhaps it's also essential.

www.ramboll-environ.com


In numbers: Floods

Image

5m - Households in flood risk areas in England and Wales.

1 in 6 - Properties at risk of flooding.

£1.3bn - Insured losses from flooding in Northern England and Wales, Scotland and Northern Ireland between December 2015 and January 2016.

529mm - UK rainfall for winter 2015-16, well above the long-term average of 330.4mm and the second highest total behind 2013-14 (545mm) since records began in 1910. It was the wettest winter on record for Wales, Scotland and Northern Ireland.

£700m - Extra flood defence funding in the 2016 Budget. In the Autumn Statement, Chancellor Philip Hammond announced that £170m will go towards

 flood defences and resilience measures, with £20m for new schemes. There is £50m to improve rail resilience and £100m for roads.