Understanding Waves

The wind blew across the surface of the smooth surface of the Gulf of Mexico. After awhile little ripples
began to form. Then they combined to form tiny swells. The water molecules themselves didn’t move
far. Instead, they passed the energy from one to the next, and this energy moved through the water
causing these swells. It was like a mouse running under a carpet. The mouse moves, but the carpet itself
There was a lot of distance, or “fetch” in nautical terms, to travel. The little swells combined to form
larger swells that were farther apart. If you measured from the water’s surface to the top of the swells,
you’d have the “wave height”. If you measure the time it takes between the peak of each swell to pass a
stationary point you have the “wave period”. The more fetch the longer the distance these swells will
travel. The farther they travel, the more they start to organize and combine. They form larger swells that
are farther apart. Surfers look for a long period and a good size wave height. When these conditions
reach shore, you can have those big, clean, rolling swells that make great surfing waves when they
A wave breaks in approximately 1.3 times its height. So, in general a 3 foot wave breaks in 4 foot of
water. Wave height is typically measured from the base of the breaking side of the wave to the top. In
some places surfers measure from the back, but the trend seems to use the measurement of the front.
It may be less macho, but it’s more accurate. This is a great trick for boaters and lifeguards. If you see a
two-foot wave breaking in the middle of the bay or ocean, it’s probably only about 2 ½ feet deep there.
This is one of many techniques water people use to “see” the bottom by looking at the surface of the
By the time this particular wave train arrives in Galveston it has traveled a couple of hundred miles.
Depending on what kind of obstacles it encounters it will behave differently. If it spends its energy on a
sandbar it becomes a “breaking” wave. Depending on how steep the slope is it will break hard or gently.
If it hits a vertical or nearly vertical barrier it can form a “surging” wave. It will bounce up but won’t
actually break. An example would be right against the rock jetties or near a breakwater. If the water
doesn’t pass through it just kind of bounces back. Good to know when making a rescue by a breakwater
or jetty.
Waves are important to understand in our line of work. They can cause or contribute to rip currents,
inshore holes and bottom contour. To understand them means to understand how to use or work
around them during a rescue. Understanding waves is a crucial part of how to save lives for ocean