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Blending infrastructure colour – an important step to managing flood risk

Grey infrastructure is moving to a blend of grey-green-blue for managing flooding. What does it all mean? Professor Chris Digman of MWH explains.

Chris Digman

For many years, grey infrastructure remained the solution of choice to manage surface water and flood risk. However, it is now becoming much more common to use sustainable drainage systems (SuDS). Whilst SuDS may often be labelled as vegetative solutions, in reality they are a combination of grey and green infrastructure.

"We need to consider blending blue infrastructure into our designs and manage surface water by creating multi-functional infrastructure using minor roads, footpaths, car parks and playing fields. It is important to note that some of this infrastructure already does this, so it’s about formally designing for it so we manage water safely."

The SuDS you choose depends on the context and opportunity (both in time and space). For example, it may not be appropriate to retrofit a green detention basin in the middle of a town centre but a water square as recently opened in Rotterdam in 2013 may be the alternate answer.

Therefore, we need to make best use of the available space we have on public and private land, being creative in our thinking and vision. We need to also spot and plan for the ‘once in a lifetime opportunity’. This is when we are redeveloping or regenerating an area so we don’t miss the chance to radically change how an area is drained (as part of a wider drainage strategy).

Ideally, we will design and maintain SuDS to help create or enhance the urban environment, generating multiple benefits. The use of SuDS in new development and across a growing number of retrofit schemes demonstrates what is achievable. Yet building momentum has been slow in moving away from the ‘below ground concrete pipes’ approach.However, we cannot always manage flood risk using grey and green infrastructure alone, as the solution size may be greater than the space available, or it is cost prohibitive.

This may particularly be the case when considering the latest indications from UKWIR (Rainfall Intensity for Sewer Design) for dealing with the increase in convective rainfall (the type that often leads to urban drainage flooding) because it is likely to be far greater in some places than previously thought.

Therefore, we need to consider blending blue infrastructure into our designs and manage surface water by creating multi-functional infrastructure using minor roads, footpaths, car parks and playing fields. It is important to note that some of this infrastructure already does this, so it’s about formally designing for it so we manage water safely. These approaches are now becoming more common on new development, redevelopment and retrofits.

"The use of more ‘natural’ SuDS akin to green infrastructure can lead to improvements in air quality and health, enhance biodiversity and ecology and be part of creating more attractive urban spaces."

Getting the right blend of colours is an important aspect to making the most of the available funds and create the greatest benefits for our communities. However, in recent years we have taken a piecemeal approach to solving individual problems, with individual solutions. This approach can close off certain options and may often only lead to grey infrastructure solutions.  However, taking a catchment approach will help us achieve more benefits.

By this I mean rather than understanding and solving individual problems i.e. if a water company just looks at flooding, we need to understand the wider issues across a catchment e.g. enabling growth, managing pollution.This has to be irrespective of responsibility if we are to gain catchment visibility of the issues. This is critical as part of the catchment approach is about working in partnership (as noted in the Drainage Strategy Framework).

When we understand the problems and critically, the subsequent interconnectivity of the different drainage networks, then we can develop integrated solutions bringing contributions between partners and a blend of interventions. It can not only help to create the expected benefits like reducing flood risk and improving water quality, it has the potential to do more. For example, the use of more ‘natural’ SuDS akin to green infrastructure can lead to improvements in air quality and health, enhance biodiversity and ecology and be part of creating more attractive urban spaces.

So be bold. Understand how we can integrate different types of blue-green-grey infrastructure working in partnership with responsible bodies and the communities and citizens we serve. If we do this, we will deliver multiple benefits by creating multi-functional assets that can provide greater resilience and more easily adapt to cope with future flooding and climatic challenges.

Professor Chris Digman is MWH Technical Director / visiting professor at the University of Sheffield and expert in integrated urban drainage.

If you would like to contact Jackie Whitelaw about this, or any other story, please email jackie.whitelaw@infrastructure-intelligence.com.