Matthew Elliott – Managing flood risk amid climate change

In 2020, the UK Government announced £5.2b of investment into 2,000 new flood and coastal defences to protect 336,000 England properties by 2027. Although a welcome step towards improving flood resilience and reducing climate change impact, this alone cannot turn the tide.

Matthew Elliott – Director, Civil & Structural, Tetra Tech – offers his perspective on the UK’s current flood risk and how Tetra Tech supports flood mitigation.

What is the current state of flood risk in the UK?

A lot of the UK coastal line is low-lying. While we do not have the same problems seen in, say, the Netherlands, if the sea level were to rise by only several metres, large parts of eastern England would go under water – such as around the Humber Estuary, River Trent, The Wash and areas around the Thames, plus significant areas in Somerset and the northwest.

Quite clearly, a lot of money needs to be invested smartly into flood prevention infrastructure, seeing as we know sea levels are rising and that a rise of up to 1.6m over the next 100 years is now considered through the planning process. Inland, we have a legacy of development inappropriately located on flood plains.

How is the UK’s approach to managing flood risk changing?

There has been a general shift away from exclusively building hard structures (e.g. embankments, walls, pumping stations etc). There is a recognition that we need to turn to a mix of solutions. With rivers, for example, we need to hold water back in the upland areas, so there is much investment looking at natural flood management techniques (something as simple as planting trees will slow water down).

Inevitably, in towns and cities, we do need flood embankments and protective walls. Of course, along with these, pumping stations are required to deal with side flows. Along the coast, defences can also take the form of walls or embankments. However, withdrawing the protected line and allowing developments of salt marshes is now a better all-round solution in some areas. There is a wide range of things that can be done.

The other side to managing flood risk is through the planning system. Substantial processes have been implemented over the years to direct new developments away from flood-prone areas unless it can be demonstrated in areas with extensive risk that continued new development there is justified. This is clearly a response to the fact that many buildings in the 60s and 70s were developed on flood plains and these developments now need significant investment in flood defences.

What are the biggest challenges for flood mitigation?

In considering new development, it is necessary to balance the objectives of different parties: a developer might look to maximise land value by increasing the number of residential units on a site, whereas the Environment Agency will want to maximise the space for water. So, it is always about finding compromises to enable viable development while still making space for water and ensuring the land is developed in a way that reduces flood risk.

A big part of flood mitigation also means recognising that in some cases, no amount of measures will completely solve the problem. There is always a degree of flood risk that people will need to live with in many areas.

How does Tetra Tech support flood mitigation schemes?

Our objective when working with either private sector developers or public bodies is to look for innovative and cost-effective ‘win-win’ solutions. As a multidisciplinary company, we can do this because we are able to look at flood schemes from many perspectives, including planning, engineering, landscape, ecology, and all aspects of design.

For example, we worked with a developer in northern Hull alongside River Hull, where the land is low-lying. Through an area action plan, it has been proposed that if existing flood defences are improved, land could be reallocated from commercial to residential. In working closely with Environment Agency and Hull City Council, we provided the evidence base enabling the adoption of the area action plan. Now we are working on the design of new adaptable defences that can be raised further in the future if climate change makes this necessary.

The double benefit is that the City of Hull secures land for new residential development to meet its housing targets, but the Environment Agency also gets a new and improved adaptable asset. That’s the kind of win-win scenario we always aim for.

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