WAVES & SURF

Ocean Waves Formation: Ocean waves are usually formed by a distant wind. Usually storms generate strong winds that act on the ocean's surface for several days. The strength of the wind, and the duration it blows have a factor on how the resulting waves will be. The area which the wind affects the surface is called the fetch. The larger the fetch, the greater the waves produced. the small waves generated by storm winds are often confused and disorganized. These waves that come from a storm are called a "sea". The sea travels in the direction that the wind was blowing. After some distance the waves become more uniform in a processes of interference, superposition and assimilation. Smaller waves are eaten by larger waves, faster will overtake the slower ones, and some waves will superimpose or cancel each other out. The organized waves that result are then called a swell, and they travel across the ocean in a wave train. The wave train transmits wave energy through the water, But not much water itself is moved forward. The swells lie low and wide in an undulating rhythm, and they do not create much resistance as they move.

This wave energy can travel across the ocean for hundreds or thousands of miles. Swell height and wave length are measured from a series of wave rider buoys. the height is an average of the larger waves in the series. The wave length when measured in time called the wave period. The time in-between two wave crests is its period. Long wave periods mean that the waves have more power stored in them.  The longer the wave period usually means that the resulting waves will be larger. Swell travels across the surface of the ocean to a depth of about half the wave height. Waves become arranged into sets. Sets are groups of waves with a pattern. Usually sets consist of some smaller waves followed by some larger ones.

Types of Breaking Waves: Waves can break in a variety of ways, the three main types of waves are Mushy rollers, hollow plungers, or surging waves. the mushy rollers are the most predictable wave, because the break gently and gradually. This is usually because the sea floor is gently sloping and and the wave breaks over a greater distance. The hollow plunger is a more violent type of wave. they are usually the result of a steeper shelving sea floor. The wave breaks more violently and the wave gets more vertical, an can even throw its crest over the front of the wave causing it to collapse suddenly. this type of wave can be hazardous to humans. the third type of wave is the surge, which doesn't need to break. the wave can swash up the shore and backwash again in a strong horizontal motion. This is especially dangerous to waders and people entering or exiting the water. Especially dangerous if the wave is surfing over rocks.

Wind on Waves: Wind is important in the creation of waves, but can have a negative effect on the waves afterward. Surfers usually prefer to surf in the mornings when the wind is light or blowing gently away from the shore in an offshore breeze. If the wind gets too strong the wave's surface will become bumpy with small wavelets. If the wind is strong on the surf, small choppy waves are produced that will mess up the surf. If the wind is blowing strong offshore it can make surfing difficult, but can result ion some spectacular spray sheeting off the crests.

Wave generated Rip Currents: We said earlier that swell does not transport water, but rather the swell transmits the energy through the water. however this changes when the waves start to break. Breaking waves begin to push water down the faces of the wave. this results in water building up near the shoreline. When sufficient water has built up it will try to flow back to the sea. The water usually flows along the shore on a Longshore current until it finds a way back to the ocean, usually is a deeper channel or where the wave action is least. the water moving seaward in a current called a "rip current". Rip currents can be extremely strong and can drag swimmers away from shore and our to sea. The rip current is usually localized, so knowing the limits of the rip will help when trying to escape it. Most novice swimmers do not realize they are caught in a rip until it has them firmly in its grasp. A novice may try to swim directly to shore against the current. This is usually futile and just wastes energy. If caught in a rip, the victim should try to swim across the flow of the rip to the side, and then swim towards shore outside of the area of the rip.

Standing Waves: Standing Waves are most common in rivers where a constant water flow over an underwater object creates a wave that breaks continuously. There are standing waves in the ocean where the strong current meets the surf or creates a wave from the flow of water on the seafloor. This kind of wave can be deceptively dangerous, because the swimmer can get held down in a hydraulic vortex. Because the wave is being continuously fed by a current, the wave is endless, and there is no pause for the swimmer to escape. Standing waves are characterized by staying in one position relative to their surroundings.

from The Safe Surfing handbook by David Dorn ©1999-2009 all rights reserved