The twin threats to London of fluvial flooding and storm surges are no longer exceptional.
On the night of Saturday 31 January 1953 and morning of 1 February 1953 the North Sea was experiencing spring tides. Northerly gales forced sea water south at the time of high tide, causing a tidal surge down the North Sea, 5.6 metres above mean sea level.
The combination of high spring tides, storm surge, winds and very large waves resulted in sea defences being overwhelmed in some locations, leading to extensive flooding. In England, 307 people were killed. Nineteen were killed in Scotland, whilst 1800 people lost their lives in the Netherlands.
A storm surge affecting the UK is caused when deep depressions track east from the Atlantic, passing close to the north of Scotland. The winds push the surface waters of the sea forward, a motion known as ‘wind drift’. On reaching the relatively shallow North Sea this water is forced southwards, eventually causing a pile up of water in the south. This is because the water cannot escape through the narrow Dover Strait and the English Channel and so gets trapped in the southern North Sea (source UK Met Office).
To protect London from storm surges travelling up the Thames Estuary, the Thames Barrier was constructed near Woolwich. It is one of the largest flood barriers with mechanised gates in the world.
The Thames Barrier has been closed 182 times since it became operational in 1982 (correct as of February 2018). Of these closures, 95 were to protect against tidal flooding and 87 were to protect against combined tidal/fluvial flooding.
The barrier is closed under storm surge conditions to protect London from flooding from the sea. It may also be closed during periods of high river flow to reduce the risk of fluvial flooding in some areas of west London. The Thames Barrier will then remain closed over high water until the ebb-tide water level downstream of the Thames Barrier has reduced to the same level as upstream. The Thames Barrier is then opened, allowing the water upstream to flow out to sea with the outward-bound tide (source UK Environment Agency).
The twin threats to London of fluvial flooding and storm surges are no longer exceptional. As shown in the figure below, there is a clear trend of increasing closures in recent times – stark testimony that extreme weather-related climate change is now a grim reality.
Thames Barrier closures since 1983 as of February 2018 (source UK Environment Agency).
Bruce Menzies, Chairman, Predict Ability Ltd (PAL)
© Copyright Predict Ability Ltd 2018. All rights reserved.
Image: The Thames Barrier (UK Environment Agency)
Author: Bruce Menzies
Bruce Menzies is Chairman and co-founder of PAL. He founded Global Digital Systems Ltd that won the Queen’s Award For Enterprise 2011. Bruce is co-author of six books on geotechnics and geology, one of which won the British Geotechnical Association Prize 2002. He holds doctorates from the Universities of London and Auckland, and is a Fellow of the Institution of Civil Engineers.