Accident signal and alarm systems.
While the bottom of the wave moving into the side. The sea level will decrease and the edge recession back out of the sea coast. If the coast is steep. To shorten the distance this retreat can be up to 800 meters. Also, the lower one. Potential flood before the crest of a wave impact side. Water flooding, this may decrease before top the next wave will move in. For example, in the case of the water level in the first drop. There may be a big wave followed another.