The Thames Estuary is particularly vulnerable to flooding for a number of reasons. The South-eastern corner of the British Isles is slowly tilting downwards and sea levels are rising. As a result, the high tide in central London is rising at a possible rate of 75cm per century.
There is another more compelling reason. When an area of low pressure - perhaps hundreds of miles across - moves eastwards across the Atlantic towards the British Isles, it raises the level of seawater beneath it by up to a third of a metre. If this 'plateau' of sea water passes north of Scotland and then down into the shallow basin of the North Sea, perhaps further heightened by strong winds from the north, it can cause excessively high surge tides in the Thames Estuary of up to four metres leading towards London. When a surge tide also coincides with a spring tide (which occur twice monthly), flooding would be a serious possibility.
The problem is made much worse when floodwater from upstream meets a high surge tide coming up from the Thames Estuary.
Teddington Weir is where the Thames becomes tidal.
On a typical summer's day about 3,000 million litres of fresh water will pass over it. On a typical winter's day the quantity will be at least four times greater, and sometimes eight times.
In the winter of 1947, the peak flow at Teddington was 61,698 million litres a day. This flow was nearly three times that of a typical winter's day and more than 20 times that of a typical summer's day.
Our new and informative section dedicated to the Thames Barrier, including visitor information, history, how the barrier works, conference facilities.
A look at our flood risk management plan and consultation for the Thames estuary.