While waves are always present on the open coast, they are not continuously active in sheltered
waters. Nonetheless, they are still the major cause of erosion in all coastal areas. Understanding how
wave action influences shoreline processes requires familiarity with several basic characteristics of
waves: height, period, and length (Figure 1). Wave height is the vertical distance between the wave crest
and trough. Wave period is the time it takes two successive wave crests to pass a stationary point, and
wavelength is the distance between successive crests.
As a wave moves through deep water (depths greater than one half the wavelength), these basic