It is important to understand the role of waves in barrier island processes.

What are they and where do they come from?

Waves are created as wind transfers energy to the ocean’s surface. As the wind blows, it pushes the water in front of it. The water gains energy from the wind due to the friction between the wind and water. In order to understand this type of friction, try blowing over a cup of water and observe the ripples or "waves" that result as energy.

Waves come in all shapes and sizes directly related to the strength and duration of the wind. Wave size increases as the strength and duration of the wind, and distance over which it blows increases. The highest point of a wave is called the crest and the lowest point is the trough. The vertical distance between the crest and trough determines the wave height, or amplitude. The horizontal distance between two consecutive crests or two consecutive troughs is called the wavelength. The wave period is the time it takes for each crest to pass a certain point, and the wave velocity, or speed, can be calculated by dividing the wavelength by the wave period (www-class.unl.edu, 2001).

Observe the circular motion of an individual water particle in the diagram below.

Waves do not carry water from one place to another, the water actually moves vertically in an orbital motion. The water moves up as a crest passes, and moves down as a trough passes. The orbital pattern at the surface sets in motion orbits of water beneath it. The vertical orbits decrease in size as energy is lost between each level, until it reaches the bottom where the orbit disappears and there is no motion. This water depth is called the wave base which is approximately 1/2 the wavelength. This means that waves in deep water do not touch the bottom, unless the water depth is less than 1/2 the wave's wavelength (www-class.unl.edu, 2001).

Typically, the waves we see along our coast originate in the open ocean far from shore. Eventually they move landward, across the continental shelf and onto the beach. As waves from offshore approach the shoreline, the waves bend as they enter shallow water due to velocity change (Pinet, 2000). When wave base touches bottom, the waves slow down. Because the wave approaches the shore at an angle, the wave base on one end drags on the bottom before the other end. This causes the wave to bend.