Thames Landscape Strategy - Hampton to Kew -

Arcadian Diary October 2007

London’s flood defences are some of the best in the UK and include many miles of walls, protective banks and of course the Thames barrier. However, the combined effects of rising sea level, more storms (leading to flash flooding), increased probability of a tidal surge and the loss of natural flood plain are increasing the likelihood of a major Thames flood sometime in the future. Therefore, the Environment Agency has reappraised the way that London will need to be protected over the coming one hundred years if it is to be protected to the same high standards we enjoy at present. This study is called ‘Thames Estuary 2100’ or ‘TE2100’. Last month the first part of the study was launched setting out the strategic direction for the Environment Agency will adopt in the management of flood risk across the Thames estuary throughout the 21st century.

In developing the TE2100 plan the Environment Agency has looked at many factors to understand current flood risk in the estuary, how this might change in the future and what the consequences of that risk to people, property and wildlife are. This process has quite literally taken years to compile due to the complex nature of the river and all of the many variables that need to be accounted for including climate change. It has been known for many years that water levels are rising in the river but what is uncertain is just how high these levels will be. For this reason, four different sea level change scenarios have been used to inform the project. This allows for flexibility in the future depending on how high sea levels actually rise. The lowest expected sea level rise is just less than one metre whilst in the worst case scenario sea levels could rise a whopping four meters above existing heights. Sensibly the Environment Agency is using the current Government guidance on sea level change to inform their decisions – a rise near to the lowest scenario.

From this, it has been possible to predict the flood risk and consequently how effective the current level of flood defences are likely to be in London. Remarkably, the TE2100 shows that with an adaptable plan for the Thames the existing flood defences have a greater safety margin than was previously understood. Under the current Government climate change scenario it looks as if rising water levels can be managed through this century and as such it is not expected that any major upgrade to the current system of defences or a major new engineering project (such as barriers or barrages) will be needed before 2030 (this of course would change if sea levels rose above the current Government guidance). In essence, our forbearers constructed much more adaptable defences than was previously thought. For example, the Thames Barrier, with some changes, will continue to provide protection for much longer than was expected as it was designed in a way that it could be modified. It really is a miracle of 20th Century ingenuity.

This all sounds very reassuring but the TE2100 study assumes that certain adaptations will be made to the way that the river and water will be managed in the future for the current level of flood defences to be effective. It is essential that these four areas are addressed.

Firstly, maintenance and minor improvement to the many walls and embankments that line the river will be needed by 2050 if the Thames Barrier and existing flood defences are to be sufficient to protect London from flooding. There is little point in having a flood defence if it does not do its job – the disaster in New Orleans showed the importance of having good, well maintained flood defences. A Government budget has been set aside for this.

Secondly, reducing the amount of water that enters our rivers from urban runoff is an important consideration if we are to reduce the need for major new flood defences. The land drainage system needs to be improved and one of the best ways to achieve this is to stop water entering the system in the first place through rain water harvesting and also the use of permeable surfaces. Where a permeable surface is used water slowly seeps into the ground rather than being channelled into drains and sent straight to the river. The impact of this is quite staggering. In July’s storm the River Crane rose by two metres in the space of one hour. All of this water ended up in the River Thames luckily coinciding with low tides. Had permeable surfaces been used more widely these water levels would have been greatly reduced – as would the risk of a Thames flood.

A further criteria is spatial and emergency planning. This will be an essential part of future flood management and this means knowledge. Authorities need knowledge to respond when the floods come. They need to know how land should be planned so as not to decrease the flood plain further. For those people living and working in flood risk areas they need knowledge on what to do if they are flooded and how to reduce the impact of this. With the right knowledge we can all prepare and live much more easily with the threat of flooding. To achieve this we can learn a lot from the Netherlands. For example, all Dutch children are taught how to prepare for a flood and what to do if they hear the flood siren. In London a survey showed that 80% of Londoners would head for an Underground station if they heard the flood warning siren go – probably the single worst thing that could be done! Like London, many Dutch houses have recently been built in the flood plain but unlike our city their structures are designed to work with rising waters. Many of their buildings are designed literally to float or to rise on hydraulic ramps when needed. This novel approach allows residents to go about their daily life as usual safe in the knowledge that when the floods come their properties are safe. Importantly it also protects the flood plain making space for the flood water to go reducing the impact that the rising waters have in neighbouring locations.

This fourth aspect ‘Making space for water ‘ is an essential part of the Environment Agency’s strategy for minimising the consequences of flood risk and a phrase that anyone who lives near to a watercourse is going to have to get used to. We need to create new ‘inter-tidal habitats’ to off-set the impacts of rising sea-levels and fluvial floods by 2030 if the current level of London’s flood defences are to be effective – put simply we need to restore many of the Thames Estuaries’s lost flood plains. This is the most sustainable and natural approach to flood risk management working with the river rather than always trying to fight and control its power. A series of suitable sites have been proposed across London, Essex and Kent to recreate the lost flood plains – not an easy task as most have already been built on!

It is important that where floodplains are restored that they have many functions. In essence they must be spaces that can be used for people to enjoy, for wildlife to flourish and for water to occasionally go during a flood event. Floodplains are wonderful places and importantly are some of the best habitats for wildlife in the UK. For most of the year they are fully accessible for wildlife and the public to enjoy – only being needed for water on those exceptional events when flooding takes place. At these times it would be reassuring to know that there are spaces for the water to go in order to protect our great city. History has taught us that to fight the power of nature in trying to control flooding is often futile and usually involves the construction of even higher walls, barriers and barrages (try to imagine how high walls stretching along the river would damage enjoyment of our glorious Arcadian river). The TE2100 plan proposes a series of achievable and sustainable measures to adapt to climate change that benefits people, water and wildlife – working with the river rather than fighting it. It’s nature’s way.

Visit thames-landscape-strategy.org.uk and follow the links on the homepage if you would like to find out more about the TE2100 project or to find out whether you live in an area that is at risk from flooding and what you can do to minimise that risk.

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