Water And Oceanography

The cause of Rip Currents and why they can be Dangerous



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A rip current is perhaps one of the most dangerous phenomenon responsible for hundreds of drowning deaths every year worldwide. With more than 80% of beach rescues occurring because of rip currents, surprisingly few swimmers understand the dangers or heed warnings. A rip current is a narrow band of powerful current running close to the shore and out to sea at a typical speed of 8kph, sometimes even faster. In shallow water, a rip current can easily pull an unwary swimmer off their feet and drag them rapidly away from the shore.

When caught in a rip current, most swimmers exhaust themselves by futilely thrashing around and attempting to fight their way back to shore because panic sets in when they discover themselves heading rapidly seaward. With some knowledge of characteristic behaviour and how to recognise a rip current, many deaths might be avoided.

The strongest of swimmers will not overcome the speed of even a fairly mile rip current should they attempt to swim directly into the flow. A rip current can extend anywhere from 50m to 800m out to sea yet they are usually less than 10m in width. The best course of action when caught in a rip is to swim with the current while angling to one side. You may be taken a fair way if caught in a fast current but once free of it, you can take your time and work your way back to the shore. The advantages of additional buoyancy characteristic in salt water should help with a relaxed side or backstroke without the danger or exhaustion. Taking care not to drift back into the rip, you are out of danger.

These dangerous currents are created because of how the shoreline is shaped, and may occur in any kind of weather or sea conditions. A deceptively mild sea might harbour a fast and dangerous rip current ready to snatch at the unwary without warning however they can be recognised with a little careful observation. Caused by ocean waves, the energy behind the wave is reflected back when the wave meet land. On gently sloping seashore, waves will push up the slope and the energy dissipates across a wide area as evident by the foaming white wash that forms smooth ramp shapes characteristic of a surf beach.

A rip current is the result of the reflected energy or receding flow being concentrated in small areas. This may be due to a submerged sand bar that create a resistance to waves moving, the energy dissipation is then restricted by the sandbar and the current begins to concentrate between the sandbar and open ocean. The edges form a release point where the concentrated current is suddenly freed of resistance and the energy equalises by the compensation of a fast band of current moving out to sea.

Sometimes it is quite easy to detect the presence of a sandbar because of the surf breaking further from shore, and the white foam dissipates in a basin like formation of deeper water between the sand bar and seashore before the wave energy actually makes landfall. It is the force of waves moving over the sandbars and pushing more water into the basins that can be reflected back that set up the imbalances in force resulting in the rip currents.

When the wave energy becomes trapped, in some cases, the backward pressure of the receding water may break through part of the sandbar, or cause water to flow parallel to the beach until it reaches a low point on the sandbar. In either case, the water that has piled up in the basin rushes out to sea once it finds an opening. The resulting rip current sucks in water from the basin and spits it out on the other side of the sandbar. It is this sideways moving water that will often characterise the presence of a rip current. These are easy to see if the water is reasonably sand-laden, sometimes they are very difficult or impossible to detect.

The danger of rip currents is widely published yet many people seem to disregard all warnings and fall victim to a phenomenon that is so easily avoided with a little care and observation. Beach lifeguards set up safe swimming areas after first inspecting the water conditions to detect the presence of rip currents. No system is perfect and rip currents can form and dissipate in a very short time. If the worse happens, do not panic, go with the current and work diagonally to one side until you are out of the flow, then work your way back to shore. It is a good idea when heading back to shore to continue in the same relative diagonal direction to avoid being caught again. When applicable, signal your distress to lifeguards and help will be with you in short order provided you keep your head and do not panic!

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