Storm surges are transient, localized disturbances at sea level, resulting from the action of a tropical cyclone, an extratropical cyclone, or a squall over the sea. (They should not to be confused with tsunamis, or tidal waves, which result from seismic disturbances). Such disturbances may be a major cause of the damage associated with cyclonic activity. Protection against storm surges may be achieved by the construction of dyke systems (as in the Netherlands), but since the most damaging surges only recur infrequently (the 1953 surge in the Netherlands which drowned 1,800 people was the first of that height for 300 years), there is an additional economic problem in justifying the construction of dykes of adequate height.
Regions particularly vulnerable to storm surges include the Gulf of Mexico, the Atlantic Coast of the USA, the Gulf of Bengal, Japan and other islands of the western Pacific which lie in the typhoon belt, and the coastal regions of the North Sea. Protection is especially difficult where there are numerous and complex estuary systems. In 1993, the UK Ministry of Agriculture spent approximately £60 million on sea defenses for the country's east coast.