Storm surges

Storm surges occur irregularly and are very difficult to predict because several processes affecting the sea water have to coincide. Two necessary factors for a storm surge are:

1) A cold front or thunder storm moves at a critical speed V over a sea area.

2) The sea has a moderate depth of only a few tens of metres and the sea bottom is even.

A front is usually associated with a change in air pressure and/or wind, which can lead to a water level anomaly. If the front is moving with a speed close to speed V in the equation V=√gh, where g=9.81 m/s² and h is the water depth, then the anomaly can be amplified due to resonance.

As the anomaly grows it can propagate itself as a series of waves. When these meet the coast a storm surge occurs. Due to the large wave length and long wave period this behaviour is interpreted as a change in water level instead of as a wave.