As you know, many coasts are barely above high tide. So if the level of the sea should rise, then they are easily flooded.
When there is a storm it pulls water upwards. Don't believe it? Then think of a tornado. You know that it lifts dirt and even trucks, high off the ground. Now imagine this kind of thing happening over the sea, but over a very big area. The air moves UP and so part of its weight is taken away. As a result the sea level rises.
It is very well known and is called a storm surge. It happened over the Mississippi in 2005 and was partly responsible for the hurricane Katrina flooding. Well, the same kind of thing happened over the North Sea in Europe on the night of 31 January – 1 February 1953 due to a fierce storm. Not only that, but the storm moved south. The North Sea is like a funnel, with its wide end at the north, and its narrow end opposite the Netherlands. All of this made the water level rise nearly 6m above average. All along the coast there were sea walls (called dykes), but no-one had expected a surge this high.
Not surprisingly, many coasts were swamped. Nearly 2000 people were killed.
Why did so many people die? In part, because they didn't know the surge was coming. It is not like today when we have 24 hour news. In those days almost no-one had a TV, and radios went off the air at night. So there was no way of letting people know.
There were many acts of bravery that night. Here is one of them: In one part of the Dutch dykes, the sea level was near the top and everyone knew the dyke was weak. At 5:30 am on 1 February the sea breached the dyke. In desperation, the local mayor ordered the owner of a tug to ram it into the gap in the dyke. The mayor’s plan turned out to be successful, as the ship lodged itself firmly into the dyke, saving many lives.
The North Sea flood of 1953 was one of the most devastating natural disasters ever recorded in the UK. Over 1,600 km of coastline was damaged, and sea walls were breached, flooding 1,000 sq km of farmland. Flooding forced 30,000 people to be evacuated from their homes, and 24,000 properties were seriously damaged.
The people of Britain and the Netherlands were determined not to let it happen again. So they began to strengthen their defences. The Thames Barrier – the big river-bed dam that can rise out of the river bed and stop the sea reaching London – and the Delta project – a vast string of dams all along the Dutch coast – were the result.
Floods are not particularly common events, but they are not that rare either. On average, a river floods about once every three years. Sometimes rivers flood more than others. The bigger the flood, the more rare it is. So the people most at risk are those who live directly beside rivers, for they will get flooded with even small floods.
Floods are all part of the way nature works. Sometimes it rains a lot and rives cannot handle all the water, so they spill over their banks and cause flooding. The floodwater is usually brown, which means it is carrying soil – we call it silt. It can only carry that silt because it is flowing quickly. When it spills over outside the banks it forms a kind of lake, and the water in this lake is still. As a result the silt settles out. When this happens time after time, the silt builds up to give level land. That is called a floodplain. It is very fertile and makes good farmland. But if people build on it they must expect to be flooded. Curiously, some people who live on floodplains are surprised when they get flooded. They don't seem to realise how the floodplain got there in the first place.
