A storm surge is a particularly high level of flooding. It is formed when additional winds sweep inland during normal high tide. As a result, the water rises even more than normal.
If a storm drives the water towards the coast and there also enters a sea bay or an estuary, it rises higher than normal there. When the water rises more than one and a half meters higher than the mean high tide, it is called a storm surge. From two and a half meters one speaks of a severe storm surge. If the water is another meter higher, it is called a very severe storm surge. Light storm surges occur several times a year, severe storm surges only every few years.
Particularly severe storm surges occur when the storm lasts for a long time. If it lasts for several high and low tide phases, the water can only partially run back at low tide. At the next high tide, it runs even higher than at the previous one.
This was the case, for example, with the storm surge of February 1962. It is also known as the “Hamburg Flood” because there was particularly great damage and many deaths in Hamburg. At that time, a water level of five meters and seventy centimeters above mean high water was measured. After this flood, the dykes were raised everywhere, so that later several even higher storm surges hardly caused any damage.
The North Sea coast in its current form was also created by many storm surges. The sea inundated many land areas. Man reclaimed and protected the land through dikes. Without dikes, large parts of northern Germany and the Netherlands would be flooded. Because of climate change, scientists expect that sea levels will continue to rise. This means that even higher storm surges will occur in the future. The levees must therefore be raised even further, or people will have to give up part of the land.