A rip current can be a diver’s best friend. This phenomenon is produced when waves break on a shallow water bar in rapid succession. Experienced swimmers can ride rip currents out through the surf zone.
“Dangerous Undertow – Swim At Your Own Risk” signs confront you at the seashore. What do the signs really mean? What do you do?
Rip currents are born when waves break on a shallow water (rock or sand) bar in rapid succession. The amount of water spilling toward the beach cannot easily return seaward along the bottom and accumulates between the bar and the shore. This excess water is held in place at the top of the water column by the continuous addition of more water from the incoming breakers. When the height of the accumulated water is sufficient, a current forms and begins to flow seaward across the lowest part of the bar. As this mass of water moves, it erodes a channel. From then on there is a continuous flow of water rushing seaward, which is called a rip current. Sandbars are more susceptible to forming channels than small rocky bars but the power of moving water will cut a slot either way.
The narrower the channel, the faster you can expect the water to move through the gap. The rip current is re-supplied by the collected water from the foamline that flows parallel to the shore. Once the water squeezes through the channel, usually beyond the surf zone, the channel typically widens and the strength and velocity of the rip are reduced.
When arriving at the beach for diving, try to survey the area from a high vantage point. Oftentimes rip currents are very visible. You can see telltale signs, such as surface currents, different colored water and kelp or aquatic plants lying in the water at different angles than neighboring species. Or, you may notice a gap in the breaking waves.
Incoming waves rarely break and spill over in a rip channel. You may notice the water looks different. The current flow against the incoming waves has the effect of increasing the wave steepness. As the crests of the waves become unstable, a small spilling breaker may result or, more likely, there will be a large number of short, steep waves. These may look like wind chop and will look different than adjacent breaking waves.
Sound like a good place to get through the surf zone? For inexperienced swimmers, riding a rip current can be a frightening, out of control experience. For those with more water skills, riding a rip current is a free ride out through the surf zone. Remember, you still have to exit through the breaking surf! Before you take the free ride out, estimate the height, speed and shape of the waves to be certain you will be able to safely return through the surf zone.
Scuba divers can gear up on shore and then enter the water where a rip current is visible. Inflate your BC slightly and kick on the surface. If the channel has sloppy wind chop looking waves, you may need to use your regulator for the swim out. Sometimes the surface is smooth enough for an easy snorkel. Once you have entered the rip, you are usually committed to riding it through the channel. Relax and enjoy the ride.
Once on the seaward side of the sandbar (which could be quite a long distance) the strength of the rip will begin to dissipate. At this point, make a right or left 90 degree turn and swim out of the rip’s path. You can then continue toward your planned dive site, either on the surface or underwater. It is extremely difficult to swim against a rip current. By making a turnout of the current, you can control a seaward swim direction or choose to let the breakers carry you shoreward.
Inexperienced rip riders are sometimes surprised to find shallow water on the sandbar just behind the breaking waves. Resist the temptation to stop and stand on the sandbar to adjust your equipment or discuss the dive plan with your buddy. Chances are an incoming wave will slam into you, tumbling you in the shallow water surf zone as it crosses the sandbar.
If you have never intentionally ridden a rip current, consider making a skin dive first. With minimal gear, it is easier to get the feel of the rip, control your body position, swim out of the rip with less effort and have less drag and equipment weight when you exit through the surf zone.
SUMMARY: While rip currents can be startling to an unsuspecting swimmer, scuba divers can use their knowledge of wave dynamics and rip currents to make an informed decision about where to enter and exit the water. If you are expecting the water flow and have planned your entry, riding a rip current can be an easy way through the surf. It is, of course, critical to have assessed the waves and know the return is within your ability.