Preventing London from Flooding - What is the Thames Flood Barrier - Broke in London


Preventing London from Flooding – What is the Thames Flood Barrier

Guest post by Jacob Stein

The Thames Barrier is a flood defense installed downstream of Central London in the United Kingdom. The movable floor defense spans a 520 meters-wide section of the road, making it the second longest movable flood protection system globally after Oosterscheldekering (The Eastern Scheldt storm surge barrier) in the Netherlands.

The Thames Barrier has been operational since 1982. It was built and installed to protect the highly dense population located on the floodplains on the west that were susceptible to high tides and storm surges meaning people had to regularly take out their electric submersible water pump.

The Thames Flood Barrier

A cross-sectional diagram of the six rising sections of the flood barrier and how they work

The barrier system divides the entire river channel into 10 different floodgates. 4 of the floodgates are installed above the river, making the outer section non-navigable to river traffic. The remaining 6, larger floodgates are installed flat on the Thames River bed. The 6 barrier gates are typically raised with a predicted high tide. When the 6 barriers are not raised in normal conditions, it allows river traffic to navigate the Thames unimpeded.

Operating the gates uses a special rotating mechanism. Each gate has a circular section in its cross-section made of hollow steel. This section fills with water, allowing the barrier to close in approximately one and a half hours.

During the inception of the barrier construction back in 1975, the idea of constructing a dam or barrier across the Thames for flood protection had been debated for years. The idea of installing a flood protection system across the Thames arose after the catastrophic floods in 1928. These floods not only left thousands homeless and displaced, it also caused the death of fourteen people.

While there was a clear need for a flood protection system on River Thames, the large number of large river vessels and the technological limitation at the time meant that only flood protection improvements on the river banks were implemented.

A few decades later, the disastrous North Sea Flood of January 1953 hit the UK, causing the death of over 300 people. This gave the impetus for flood barriers to be constructed. While London did not experience devasting flooding during this event, the scale of flooding in other parts of the country renewed interest in London’s vulnerability to floods.

A committee investigating the floods recommended an investigation to be done on the possibility of installing a barrier. The Sir Herman Bondi 1967 review, occasioned by the devastating 1962 Hamburg floods, occasioned accelerated progress of the proposal to install the barrier. Consequently, the Thames Barrier Act was passed in Parliament in 1972.

The Thames Barrier at Silvertown, north bank of the river, in open (normal) operation

Each main gate of the barrier is over 20 meters high. Importantly, every gate can withstand a tidal surge nearly 10 meters above the normal tide level. As such, the barrier can protect London from a 1-in-1000-year flood.

However, the barrier has to be raised frequently. With the predicted slow subsistence of southeast England (as part of post-glacial rebound) and changing tidal levels, there is a need to raise the barrier height to offer the intended protection. Furthermore, with the predicted rise of sea levels occasioned by human-induced climate change and London’s increasing population density, the barrier will likely be called into action frequently until its replacement date in 2060.







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