Don't Get Carried Away on Labor Day
By Phil Keillor and John Karl
MADISON, Wis. (8/31/99) – Several recent drownings at Lake Michigan beaches highlight the importance of understanding currents and how to escape from them, according to Jim Lubner, Water Safety Specialist at the University of Wisconsin Sea Grant Institute.
The two most important currents to know about are longshore and rip currents, Lubner said. Longshore currents flow along the shoreline, and rip currents flow roughly perpendicular to the shoreline on the surface of the water.
"You always want to swim perpendicular to the currents," Lubner said. "In the case of longshore currents, that’s perfectly natural. The current will carry you along, parallel to the shore, and you should just swim toward shore."
Rip currents are a little trickier, Lubner said.
"With rip currents, you get pulled out away from shore, and your natural instinct may be to swim directly towards shore, against the current. But it’s best to swim at right angles to the current, which in this case is parallel to shore. That way, you get out of the current the fastest. Then you can swim towards shore much easier," he said.
"These currents are usually pretty narrow, so you can get out of them in a short distance," said Philip Keillor, a UW Sea Grant Coastal Engineering Specialist.
"Currents are the result of powerful forces at work," Keillor said. "When strong winds blow towards shore, they build up high waves and push water towards the beach. Between the shoreline and the breaking waves, the water piles up higher than the lake level. Gravity then pulls this elevated water back into the lake, and this creates the currents."
A third kind of current is called an undertow, Keillor said. "Swimmers at the surface won’t be affected much by the undertow, because they’ll be above it. If you’re near shore, it could knock you down, but you can just stand up there."
Of course, the safest strategy is to avoid the currents altogether. Knowing when and where they usually form will help.
Longshore currents are most likely when the wind and waves come onshore at an angle other than perpendicular to the shore, Keillor said. The current will then flow downwind along the shore. For example, if you’re standing on shore facing the lake and the waves and wind are approaching from the right, the longshore current will probably flow to the left.
Rip currents form when a longshore current turns away from the shore toward the open lake. They can also flow alongside large solid structures extending off shore. Swimmers, waders, wind surfers, divers, and fishers should stay away from the water alongside harbor breakwaters and jetties, long solid piers or groins, and large shoreline rock outcrops when the water is rough.
Rip currents may also flow along underwater structures such as nearshore reefs and troughs in the nearshore lakebed.
One sign of rip currents is a stretch of breaking waves whose heights are lower than the waves to either side. Other signs of rip currents are patches or lines of foam and debris, and discolored water moving away from shore.
"Remember that the dangers of currents multiply when the water is cold," Lubner said. "Cold water drains heat from the body very fast and interferes with muscle operation and coordination. You can’t swim as far or as fast in cold water."
For More Information:
Jim Lubner, Water Safety Specialist, (414) 227-3291Conceived in 1966, Sea Grant is a national network of 30 university-based programs of research, outreach and education dedicated to the protection and sustainable use of the United States' coastal, ocean and Great Lakes resources. The National Sea Grant Network is a partnership of participating coastal states, private industry and the National Sea Grant College Program , National Oceanic & Atmospheric Administration , U.S. Department of Commerce. The University of Wisconsin Sea Grant College Program is administered by the Sea Grant Institute on the UW-Madison campus in Madison, Wisconsin.
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last updated 16 June 2000
posted 8-31-99 by Karl
www.seagrant.wisc.edu/communications/news_releases/GreatLakesCurrents.html
