Thames Flood Barrier

As a geologist, I know that no project is complete without a field trip, so I took myself off to the Thames Flood Barrier - London's very own adaptation to flooding and sea level change. In true field trip fashion, it rained, and was much colder than anticipated, but at least this time I didn't fall waist deep into a bog...


Much of London is built on the flood plain of the River Thames, and as such is at risk from flooding from high tides and storm surges from the North Sea. Storm surges occur when low pressure systems in the atmosphere above the Atlantic causes a relative rise in sea level, this can be particularly dangerous if the pressure system moves into the North Sea where it is relatively shallower (Environment Agency). Storm surges in conjunction with high tides can cause serious flooding in London.The Thames Flood Barrier was built in response to a disastrous flood in 1953 that killed over 2000 people in countries around the North Sea, including more than 300 people in the UK. East London was badly flooded, with over 3000 people were waiting overnight for rescue boats in Plaistow and West Ham (Thames Barrier Information Centre (TBIC)).


So the solution? Build one of the largest moveable flood barriers in the World, obviously!

Work started in 1971, with raising of the banks along the Thames, then in 1974 construction of the barrier began. Work was finished in 1982, and the barrier was first used in February 1983 (TBIC).

If it wasn't for the barrier, standing here in January 1993 would have been a very bad idea.

But as we know sea level is rising. Tides in the Thames estuary are rising by a rate of 60cm every 100 years. This is especially high because London is 'sinking' into the underlying clay, post-glacial isostatic adjustment is causing this part of the UK to subside, and because the weather is becoming stormier (TBIC). With a relatively higher sea level, storm surges and high tides don't need to be so big to cause as much damage, or even overcome the barrier.


The risk of London flooding is increasing with rising sea level. This is quite apparent when you look at this graph showing how many times the barrier has been shut to protect London since it was built. In April this year the barrier had already been closed a record 48 times!

 

Necessary closures of the barrier are highly variable, but the barrier is being closed more than was originally planned for when it was built (Environment Agency)

But what does this mean for the future?


The barrier was designed to cope with 100 years of rising sea level at a rate of 8 mm a year. But then a new flood management strategy will be needed. The Environment Agency has forecast that the current barrier will start to fail between 2030-2060 and has drawn up the Thames Estuary 2100 plan to discuss how we can minimise the effects of rising sea level. They suggest a combination of natural mitigation such as improved floodplain management and reintroducing intertidal habitats, and more man-made solutions such as building new bigger barriers further downstream.


Most importantly, they have recommended that flood defences are continually assessed and updated. I think this point is really crucial to coping with sea level rise all over the world. There is never going to be a final solution that we can put into place and forget about. Sea level is changing all the time and not always in predictable ways, warming climate will change the patterns of precipitation and storms and therefore the likelihood of flooding. So we really can't quantify the extent of flood defence measures that we will need in the future, and I think the most important thing is to be aware of that.