Wave Types

Here is a graphical representation of wave
type with the associated beach slope.

      Before beginning a surf observation, the observer must have a basic understanding of waves and their dynamics. The surf zone is defined as the area between the first breaker shoreward to the beach. Breakers form as a wave enters water which is shallower than half its wave length. The water near the bottom of the wave begins to feel bottom, and is retarded by friction, causing the wave to increase in height until it becomes too high for its motion, and falls over into the preceding trough.
      There are three types of breakers in the surf zone; spilling, plunging, and surging. The slope of the beach and the types of waves approaching the surf zone determine which type of breaker is going to be predominant.

      Spilling: breaks gradually over a distance. White water forms as the crest and expands down the face of the breaker. Only the top portion of the wave curls over however. Light foam may wash gently up the shore. This type of wave is normally found with a flat bottom beach. It is usually the most observed type of wave.

      Plunging: the wave peaks up until it is an advancing vertical wall of water. The crest advances faster than the base of the breaker, curls, and then descends violently into the wave trough. This type of breaker sometimes causes an explosive sound as trapped air escapes behind the wave. It is usually found on a medium to steep sloping beach, with little wind or an offshore wind.

     Surging: advances at the same rate as the base of the breaker, it surges up the beach as a wall of water. It may or may not be accompanied by white water, and is usually found on very steep beaches.

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In a Spilling Breaker, the energy which the wave has transported over many miles of sea is released gradually over a considerable distance. The wave peaks up until it is very steep but not vertical. Only the topmost portion of the wave curls over and descends on the forward slope of the wave, where it then slides down into the trough . This process is why these waves may look like an advancing line of foam.

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In a Plunging Breaker, the energy is released suddenly into a downwardly directed mass of water. A considerable amount of air is trapped when this happens and this air escapes explosively behind the wave, throwing water high above the surface. The plunging breaker is characterized by a loud explosive sound and are more commonly found on the west coast of North America and the Pacific Ocean.

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Surging Breakers

In surging waves, the wave crest tends to advance faster than the base of the wave, which would suggest the formation of a plunging wave. However, the wave then advances faster than the crest, the plunging is arrested, and the breaker surges up the beach face as a wall of water which may or may not be white water. These waves are usually found on beaches with a very steep slope.

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Spilling Breakers Spilling waves break gradually over a distance. White water forms at the crest and expands down the face of the crest and may wash gently up the shore.	Plunging Breakers Plunging waves are usually found on beaches with a medium to steep slope, with little wind or an offshore wind and long-period swell.	Plunging Breakers Plunging waves peak up until it is an advancing vertical wall of water. The crest advances faster than the base of the breaker, the crest curls, then descends violently into the trough.

The graphic (left) shows how the slope of the surf zone can effect what wave type will be experienced. The top graphic shows the gently sloping beach and a spilling breaker type. The bottom graphic shows an abrupt change in slope and the plunging breaker type.

Right: This is an example of shoaling. It occurs when there is a reef or bar offshore giving the impression that the surf zone is farther out than it actually is.