Thames Landscape Strategy - Hampton to Kew -

Arcadian Diary July 2004

The Thames is a powerful natural force and like all rivers can create and destroy. It has, with time, been modified and tamed by humans but as with all natural forces it is in a constant state of change. One of the most important initiatives along the Thames at the moment is to find new ways to manage this change and in particular what to do in response to rising sea levels and the increasing risk from flooding.

The Thames floodplain is home to 1.25 million people, major infrastructure and areas of high historical and natural conservation value. The Thames has some of the best flood defences in the UK, protecting London and the Thames Estuary to an extremely high standard. However, these flood defences are getting older, and as climate is changing the time has come to plan for the next generation of flood management measures that will account for population growth, evolution in land management practices and the biodiversity and use of the riverside.

In London, the floodplain is at risk from a number of sources including the twice-daily rise and fall of the tide, North Sea surges, fluvial floods from the upper Thames and urban run-off. In the capital alone there are a staggering 429,000 properties at risk from tidal flooding and 85,000 properties at risk from fluvial floods. The estimated value of this property is £80billion and home to one sixth of London’s population. It is responsibility of The Environment Agency to maintain the high standard of flood defences.

It is now commonly accepted that the effects of climate change will have severe impacts on all of our lives. Heavy rainfall will be more frequent, storms will be greater and sea levels are rising by 6mm a year. It is anticipated that the flow of the Thames as it passes over Teddington Weir will be 20% higher by 2050. These changes may sound low but the consequences of flooding on homes, businesses, power supplies and transport would catastrophic.

This said, the Thames Barrier provides London with one of the best flood defences in the world. But what is little known is that the operation does not just involve the closure of the main barrier but also 8 other major flood barriers on the Thames tributaries to stop flooding ‘by the back door’ and 380 smaller movable defences at great expense. The Barrier was constructed to provide protection to 2030, however, it was designed to allow for changes in the way the river works and as such the defence will continue to operate well after this time.

What is of concern is the frequency of use. The Barrier was designed to be shut 3-4 times a year. As sea level rises and fluvial flooding increases however, the number of closures is increasing. For example in January 2001 alone the Barrier was shut 24 times and in January 2003 24 times. It is this increased usage that is causing concern on the wear and tear to the infrastructure, disruption to shipping and fish migration, cost and the consequences of closure on communities downstream of the defence.

These flooding events in 2001 and 2003 were exceptional but are on the increase and importantly the consequences for riverside communities in our part of London is significant. The Barrier closures that took place in 2001 and 2003 were mainly to protect the area between Kingston and Richmond as at the time a series of very high floods were moving their way down the river from the upper reaches of the Thames and meeting high water in the Estuary downstream of Teddington. The problem we face is one of where does the water in a freshwater (fluvial) flood go when the tidal river is full during a high tide. Without the closure of the barrier river levels would have been 1.5m higher in Richmond and Twickenham causing huge damage to property and devastating the local community. What the Environment Agency is concerned about is what will happen in the future in light of the anticipated changes in sea level and use of the Thames Barrier.

In the past, the solution to flood water between Kingston and Richmond would have been to construct flood walls and embankments but these are increasingly unpredictable and would have a devastating impact on the historic and natural landscape and the way that people enjoy their riverside.

A European initiative has been established (funded by the EU) to investigate new ways to make space for water during exceptional events by allowing managed inundation at certain points along the river. This flood risk management initiative has been called FLOODSCAPE and is a joint project between the UK, Germany, Nederlands and Belgium.

FLOODSCAPE is trying to find local solutions to these problems that address the needs of local communities, wildlife and heritage. Six sites have been chosen across Northern Europe to investigate how this programme will work. In the UK, three sites have been included in Essex, the North Kent Marshes and Ham Lands.

The flood plain, both sides of the river to include Teddington and Twickenham has been surveyed and modelled so that the way the river floods at present and could flood in the future can demonstrated. This has been carried out on 10m square grids and provides a level of accuracy unprecedented before. The task now is to use this data to devise a community based solution that manages flooding whilst taking into account the areas wildlife, use and history.

Ham Lands were for centuries managed as grazed wet meadows but following extensive gravel extraction and subsequent in filling with bomb rubble their character was altered and in particular the capacity for the area to accommodate flooding reduced. The diversity of plant life created by the variety of soil types from the bomb rubble though was exceptional but once grazing by cows ceased in the 1970,s much of this diversity has declined and scrub and invasive species now dominate much of the area. The opportunity to restore sections of Ham Lands to meadowland would allow the river to flood these areas during exceptional floods (estimated at only 2-3times per year and for short periods of time). This would divert water away from the more populated areas in nearby Twickenham, Petersham and Richmond. At the same time the lost Great River Avenue could be restored, acting as an additional flood barrier to protect Ham and Petersham and through land management improvements the declining diversity of the grassland turned around.

In the last couple of weeks a series of options have been published by FLOODSCAPE to provide local people with a way to try and understand how flooding can be accommodated in order to reduce the impact on property and at the same restore and enhance the conservation value of area. These range from a do-nothing approach to a maximum flood alleviation option. A vast array of factors have been included in developing the models including litter, long-term management, funding, recreational use, wildlife and traditional countryside management techniques. FLOODSCAPE is an important development in the on-going renaissance of our river and one which I am sure many people will want to find out more about. The most up to date information can be found on the web by visiting www.floodscape.net or you can write to me at Holly Lodge in Richmond Park and I will pass on your letters to the Environment Agency.

River Fact
In a recent survey carried out to gauge how much people in London knew of what they should do in a major flood a rather worrying 97% of those questioned said that if they heard the flood warning siren they would take shelter in an Underground station!

> Read other Arcadian Diary entries
> Back to the homepage