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Sandbars

12 Jun Beach Safety, Chief's Column, GIBP News, On The Beach | Comments Off on Sandbars
Sandbars
 

I got an interesting call from a local woman who told me to write about what it means to “step off a sandbar” and why that can cause someone to drown. The woman, now in her 90’s, said when she was young she had to hand her 3 year old to someone else and trust him to bring her child to shore when she “stepped off a sandbar” herself.

Most of what we focus on in beach safety involves rip currents. Rip currents, responsible for 80% of rescues in the ocean (and presumably drownings) run roughly perpendicular to shore and are formed when water brought in by waves has to find a way back out past the surf zone. In Texas our strongest and most predominant rip currents are formed near a structure like a jetty. This is why we recommend people stay away from the rocks and why we post our towers on the seawall near the groins. If you’re caught in one, float with it and you’ll likely return to shore on your own. If you’re a good swimmer, try swimming parallel to shore, but never try to swim directly into a rip current (directly to shore).

The phrase “stepping off a sandbar” refers to times when someone is standing in relatively shallow water and currents or waves push them from the shallow sandbar into a trough where the water is deeper. Just as is the case with rip currents, if you simply relax and float you’ll be fine, but bad things happen when people panic or choke on water.

At our beaches we have a sandbar and trough system, both of which run parallel to the shoreline. As you walk into the water from shore you’ll step into deeper water, then shallower water, than deeper, shallower, and so on. Gradually it gets deeper and deeper but we have 4-5 sandbars and troughs before it gets deep enough for the bottom to level off. The sandbars farther from shore need bigger waves to break on them but the first couple are easy to spot by the breaking waves even from shore. Waves break in water about 1.3 times their height, so an experienced guard or person can tell water depth by looking at the waves. The waves don’t break in the deeper water so the troughs are calm looking areas between the sandbars.

The difference in depth between the sandbars and troughs is exacerbated by long shore current, which runs parallel to shore. The longer and harder it runs, the deeper the troughs. Generally when the current lets up the bottom levels off to normal in a couple of days, but this past week it was so calm that the normal “jiggling” of the bottom sand didn’t happen and there was a neck deep trough very near the shoreline all week.

Generally the most important way to be safe is to swim near a lifeguard, but it’s also a good idea to stay in shallower water than you would in an artificial environment.