Posted on Jul 28, 2014

Natural flood defences can help protect our coast and rivers

During last winter, the UK saw some of the worst flooding it has had for many years. With homes and farmland under feet of water, the questions that have inevitably followed focus on how flooding on such a scale can be prevented in the future. Daniel Bastreri is a principal marine consultant at leading UK ecology consultancy Thomson Ecology. In this article he discusses the different man-made and natural solutions that may help to solve this difficult issue.

From an ecologist’s viewpoint, flooding is a natural phenomenon that happens the world over. The difference is how we deal with it. Back in the mists of time, flooding was a fact of life in the UK – London regularly flooded and there are medieval chronicles of Whitehall Palace surrounded by water. Similarly if you look at Norfolk during the pre-Roman era, a great part of it was made up of small islands accessible only by causeways or boats. Water was an accepted part of life and locals knew that flooding was a very real possibility and planned accordingly.

In recent years, we have come to rely heavily on man-made hard flood defences and adaptations of the landscape. Purpose-built structures, like the Thames Barrier for London, have done a lot to help protect big urban areas from flooding and there has been heavy investment in hard sea defences to stop coastal towns from flooding. However, man-made flood defences are costly to install and maintain, and can realistically only partially solve the problem. Likewise, interventions such as river dredging have a high cost of maintenance and, in some instances, an adverse effect on the ability of the land to hold enough water for farming and consumption. As a society we need to be more strategically prepared for potential flooding and think about how nature’s natural flood defences can be utilised more fully to our advantage.

Thomson Ecology works closely with planners and developers at the early stage of projects, providing strategic advice on biodiversity management of proposed schemes. This can include solutions that effectively protect and improve the natural environment. As far as understanding our river systems is concerned, the UK is well ahead of the game. As part of its role, The Environment Agency collects data on water quality, water levels and the natural flow of rivers and tributaries in England and Wales. River dredging has been heralded, particularly by residents on the Somerset Levels, as the answer to all their flooding problems. In truth, it may help but only as part of a wider solution. As ecologists, we know that dredging can be detrimental to water capture, water quality and biodiversity in rivers, estuaries and coastal areas. It needs to be used in an informed and fully assessed way, and although it can be part of the answer to flood prevention, it is not the only solution. A key issue going forward will be planning and land management around rivers and river catchments.

Dredging can be very effective in coastal waters where rising sea levels mean that shorelines often require repair after storms and flooding. Eastbourne is a good recent example where the Environment Agency and local councils continue using dredged material to replenish parts of the coastline that were battered by high winds and waves during the recent bad weather. In some cases, sand or gravel accumulate at one end of the beach, starving the other sections of material. This material is then moved (recycled) back and distributed along the coast using rolling machinery. When this is not possible, dredgers collect material from the seabed and place it on the shore by ‘rainbowing’, which is using pressurised water mixed with dredged sand to deposit the sand on the beach. As an ecology consultancy, we work with dredging companies, local authorities and harbour authorities to provide appropriate ecological surveys as part of their consents process for dredging operations for harbour and waterway maintenance.

Alongside man-made solutions such as dredging, the UK also needs to look how natural flood defence schemes can help to prevent flooding. There are some excellent examples around the UK of natural flood defence schemes where nature is being used to literally hold back the water. Wallasea Island’s Wild Coast project is a scheme that Thomson Ecology has been working on, with Crossrail and the RSPB, in Burnham-on-Crouch in Essex. This is a ground-breaking project that aims to combat the threat of coastal flooding by recreating wetlands, mudflats and saltmarsh, lagoons and pasture. The expectation is that the project will help the coast and its wildlife to adapt in the face of rising water levels, which may result from climate change.

The Wallasea Island Wild Coast project and others like it demonstrate that certain types of vegetation and landscape are very good at retaining water. Plants and animals that live in these sorts of very wet environments are adapted and thrive in these conditions.
Another, similar, project that Thomson Ecology has been working on is Steart Marshes in Somerset, which is a great example of how the natural environment can help combat rising sea levels and increasing risks of flooding . As part of this project the Wildlife and Wetlands Trust and the Environment Agency are turning hundreds of hectares of the Steart Peninsula into new saltmarsh and freshwater wetlands. As well as replacing threatened habitats for wildlife, this vast new landscape will continue to be productive and useful as it will be farmed in association with local graziers, and will increase protection for Steart village against flooding.

Whether it is sea or river, the fact is that we as a country have to plan for potential flooding within new developments that are near water. Some of this may be a question of ensuring that new construction is built to withstand flooding and some of it may be through ensuring that we preserve, manage and enhance flood plains and salt marshes, allowing nature to do its job. There are so many good examples of nature at work that they shouldn’t be ignored.

Developers and local authorities need to use natural flood defences wisely, retaining some of the natural environment that, with management and improvement, can help mitigate some of the effects of flooding. With the human population growing at the rate it is, there’s a limit to the environment for this sort of expansion – we have to adapt and plan in different ways.
Shoreline restoration in the face of rising sea levels and flood risk is increasingly about preserving natural flood defences and working to minimise risk. There is a place for hard defences and dredging as part of human solutions to flood prevention and we work hard with our clients to ensure that where dredging is necessary, the natural environment is monitored effectively. Dredged material can also be used in a sustainable way to create green space and biodiversity-rich environments when sediments are clean and not contaminated with toxic waste. Wallasea Island is a particularly good example of how creating green areas can help to protect biodiversity and create a natural flood barrier that is rich is wildlife.

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