Growing up at the beach, of course lots of people took their dogs to the beach, just as they do today. One day a beautiful dog disappeared into the Ocean in Dewey, in what many thought was a rip current. For those of you with dogs that enjoy the Ocean be aware that they are just as much at risk as their humans in getting caught in a Rip. It’s our job to assess the Ocean’s status to be sure they don’t fall victim as this dog did. Unfortunately we can’t teach them to swim parallel to shore. —Sandy
Where and Why Rip Currents Form
C
oastal scientists have been investigating rip currents for more than 75 years. This research has been conducted through field observations, measurements, laboratory measurements, wave tank experiments, computer and numerical modeling. The mechanics of rip current development are complex and involve interactions between waves and currents, waves and water levels, waves and the shape of the near shore bottom (bathymetry), as well as wave-wave interaction. Rip currents can occur along any coastline that has breaking waves. Scientific investigations of wave and current interactions along the coast have shown that rip currents are likely present on most beaches every day as a component of the complex pattern of near shore circulation. As waves travel from deep to shallow water, they eventually break near the shoreline. As waves break, they generate currents that flow in both the offshore (away from the coast) and the alongshore directions. Currents flowing away from the coast are called rip currents. Along all coastlines, near shore circulation cells may develop when waves break strongly in some locations and weakly in others. These
weaker and stronger wave breaking patterns are most often seen on beaches with a sand bar and channel system in the near shore zone. A rip current forms as the narrow, fast-moving section of water travels in an offshore direction. Rip currents can also result from a wave's natural variability or when a current traveling along the shoreline encounters a structure such as a groin or jetty and is forced offshore. Rip current strength and speed varies. This variability makes rip currents especially dangerous to uninformed beach goers. Rapid fluctuations or pulses in wave groups can quickly generate rip currents with velocities measured up to eight feet per second.
Waves, Currents and Water Level Variations As waves break along a shoreline or over a sandbar, an increase in water level occurs. This increase in water level is known as “set-up.” The increase in water level is especially evident as waves break over a sandbar, resulting in an increased set-up of water on the landward side of the bar. Thus, waves breaking over a sandbar can result in mass transport of water
Delmarva Unleashed Late Summer 2017
17
