The wind blows across the smooth surface of the Gulf of Mexico. After a while, little ripples begin to form. Then they combine to form tiny swells. The water molecules themselves don’t move far. Instead, they pass the energy from one to the next, and this energy moves through the water, causing these swells. It is like a mouse running under a carpet. The mouse moves, but the carpet itself doesn’t.
There is a lot of distance, or “fetch” in nautical terms, to travel. The little swells combine to form larger swells that are farther apart. If you measure from the water’s surface to the top of the swells, you 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 sized wave height. When these conditions reach shore, you can have those big, clean, rolling swells that make great surfing waves when they break.
A wave breaks in about 1.3 times its height. So, in general a 3-foot wave breaks in 4 feet 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 2-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 water.
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 lifeguards.