BACKGROUND: A professor at the University of Delaware has created a comprehensive computer model that predicts the physical processes in the area from the high tide mark on shore to a depth of 10 meters, called the nearshore ocean.Wave weight, current movement and naturally occurring sediment transport, are analyzed by computers to from a computer model. The model allows weather forecasters to quickly predict dangerous surf conditions and issue immediate warnings. It can even predict some dangerous events weeks before they occur. Swimmers and life guards have more tools to identify rip currents, for example. The model would also be useful for builders designing shore properties.
WHAT ARE RIP CURRENTS? A rip current is a strong flow of water returning seaward along the shore. When wind and waves push water to the shore, the previous backwash is often pushed sideways by the oncoming waves. The backwash streams along the shoreline until it finds an exit back to the sea. The resulting rip current is usually narrow and located in trenches between sandbars, under piers, or along jetties. The current is strongest at the surface and can dampen incoming waves, which might make the area seem deceptively calm. That's one thing to look for when searching for rip currents: unusually calm waters. The color of the water may be different from the surrounding area, and the waterline will be lower on the shore near a rip current.
IT'S NOT THE UNDERTOW: Many of the deaths resulting from rip currents are wrongly attributed to an undertow. The two are related, but distinct. Rip currents occur if there's a place along the beach where the incoming waves aren't as strong, so that the escaping water goes through that weak spot. If there is no spot with weaker surf, the accumulated water flows down and under the waves and back out to sea, forming an undertow.
TIDES AND THE MOON: Rip currents are sometimes erroneously called "rip tides." They are not tides, although particularly low tides can lead to stronger rip currents. What are tides? The strength of gravity depends on the distance from the source; the closer you are, the stronger the "pull" that you feel. The moon's gravity acts on the earth, but the diameter of the earth is large enough compared to the distance of the moon that one side of our planet -- the one nearer the moon -- feels the moon's gravity much more strongly than the side further away from the moon. In effect, the earth is "stretched" by the difference in the moon's gravity across the earth, and this gives rise to the tides. That's why there are two tidal bulges on the earth, one on the near side, and one on the far side.
SAFETY TIPS: The most common advice for escaping a rip current is not to panic and try to swim against the current directly back to shore. People become exhausted very quickly and can easily drown. Instead, you should swim parallel to the beach and then let the waves bring you into shore.
The American Geophysical Union contributed to the information contained in the TV portion of this report.
