Chapter 2- The Diving Environment The Diving Environment knot, but the speed increases with wave height, increased angle of waves to the shore, and the steepness of the beach. The intensity of a longshore current is greatest inside the surf zone, diminishing as you move away from shore. A longshore current can move you “down” the beach, perhaps to an undesirable exit area. Visibility near shore will be reduced by a longshore current which transports sediment down current. Items dropped near shore will tend to move in the direction of the longshore current. A strong longshore current tends to form a “cut,” “trench,” or “inshore hole” in the surf zone, especially on steeply sloping beaches. When wading on what you might consider a continuous incline, you may suddenly and unexpectedly find yourself in water over your head. Beaches where longshore currents are likely should be evaluated prior to entering the water, so actions can be taken to compensate for any effects. The currents can often be detected by watching floating wood, birds, or other debris for lateral movement. If the surf is so large that a strong longshore current is produced, diving is inadvisable. Rip Currents A rip current is formed by water seeking its own level (figure 2-14). When a large set of waves approaches the beach, the surge of the water “piles up” the water on the incline of the beach. This water, being higher than the average water level, seeks to return to that level. If the return occurs through a deeper section of the offshore bottom, then a rip current may form. Or, the water may cut its own channel, first at one place, then at another on an unpredictable schedule. The distance a rip current may flow varies in length from a few meters (or yards) to a kilometer (0.6 mi) or more. These currents are the leading cause of surf rescues of swimmers and can pose problems for divers when encountered unexpectedly. The intensity of a rip current is greatest during the lull in a set of waves. There is a direct relationship between the size of the surf and the intensity of a rip current. Larger surf equates stronger current. The Anatomy of a Rip Current There are four types of rip currents: • Permanent–Formed by a rock channel or subsurface topography which changes very little. Permanent structures such as piers, jetties, pipelines, or outcroppings can also create rips. • Fixed–A fixed rip is second in longevity of location only to a permanent rip current. A hole or gully in the offshore bottom can create a rip current that can last from several hours up to several months. • Flash–Temporary in nature for any given location. Caused by a large surf buildup during a short period of time. They appear suddenly and without warning and are relatively short-lived. • Traveling–A traveling rip current is propelled along a shore frontage by a strong longshore current. This type of rip may travel over large segments of beach before dissipating itself. 43 FIGURE 2-13. LONGSHORE CURRENT Rip Current Sand Bars Sandy Beach FIGURE 2-14. RIP CURRENT
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