We have used the number of Thames Barrier closures as the second indicator for assessing London’s flood risk. This is as part of the London State of the Environment Report.
The number of times the Thames Barrier closes is a direct indication of the number of high tides, storm surges, and high river flows affecting the Thames Estuary. It also shows the effectiveness of the barrier in protecting London.
About the Thames Barrier
The Thames Barrier is closed under storm surge conditions to protect London from flooding from the sea. It may also be closed under periods of high flow over Teddington Weir to reduce the risk of fluvial (river) flooding in some areas of west London including Richmond and Twickenham.
Dangerous conditions can be forecast up to 36 hours in advance using the Storm Tide Forecasting Service at the Met Office and information from the barrier's own computer analyses.
Number of closures
The graph above shows that the Thames Barrier has been raised 119 times since it became operational in 1982 (76 were to protect against tidal flooding and 43 were to alleviate fluvial flooding).
Closures of the barrier have increased through the decades. During its operation, just over two thirds of closures have been since 2000. It was closed four times in the 1980s, 35 times in the 1990s, and 80 times since 2000.
Between 2004 and 2008, all closures of the barrier were to protect London from tidal flooding. In 2009 and 2010 the barrier was closed to protect against fluvial flooding. The barrier had not previously been used to protects against fluvial flooding since 2003. During the first week of 2010, the barrier was closed five times as high fluvial flows and the high spring tides coincided.
Future use of the barrier
As sea level rises, the Thames Barrier will have to close more frequently to prevent overtopping of the flood defences upstream of the barrier.
The risk of the barrier failing is increased the more it is closed, and frequent closures will affect the maintenance regime.
The current recommendation of the Thames Estuary 2100 project is to set 50 as the maximum number of times the barrier should close each year. This will reduce the chance of it failing to unacceptable levels. This is a key constraint in the Thames tidal defence system and reaching this figure will mean we will need to intervene and improve the tidal defence system. The onclick="window.open(this.href);return(false);" onkeypress="window.open(this.href);return(false);">Thames Estuary 2100 summary document estimates that the design limit of 50 closures begins to be exceeded from 2135 onwards.