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An Examination of Rip Current incidents on the Great Lakes. Megan Babich NWS Marquette, MI. Overview. What is a rip current ? Conditions necessary for rip current development The Great Lakes Current Incident Database

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Presentation Transcript
  • What is a rip current?
  • Conditions necessary for rip current development
  • The Great Lakes Current Incident Database
  • Comparisons between ocean rip currents and Great Lakes rip currents based on collected data
what is a rip current
What is a rip current?

A narrow jet of water moving swiftly away from shore, roughly perpendicular to the shoreline.

A way for water piled up on shore to escape back into the lake/ocean.

Grand Marais, MI:

Lake Superior

Photo Courtesy of Don Rolfson, NWS Marquette

Shepard et al. 1941

how do r ip currents develop
How do rip currents develop?
  • Variations in the stress on the surface of the water lead to areas of high and low pressure.
  • Converging longshore (shore parallel) currents cause an outward flow of water: a rip current

Shepard et al, 1941; Shepard and Inman 1950; McKenzie 1958; Bowen 1969; COMET

what causes these variations in stress
What causes these variations in “stress”?
  • Differences in wave characteristics:
    • Height
    • Period
  • Tidal influences/Seiches
  • Shoreline Structures
the great lakes current incident database
The Great Lakes Current Incident Database
  • 346 current related incidents collected from media articles/eyewitness reports
  • Weather and lake conditions during incidents documented
  • 2002-2011 swim seasons
  • Media coverage of incidents
  • Media assumptions and error
  • Limited observations of nearshore environment
  • Observations may not be representative of true environment
why is this important
Why is this important?
  • Rip currents responsible for at least 150 drowning fatalities per year nationally (USLA, Lushine 1991)
  • Rip currents responsible for at least 10 drowning fatalities per year on the Great Lakes (NWS MQT database)

Ludington, MI:

Lake Michigan

Photo Courtesy of Univ. of Michigan Coastal Engineering Department

why is this important1
Why is this important?
  • NWS MISSION: Protection of Life and Property…
  • Knowing the conditions and locations necessary for rip current development on the Great Lakes will help forecasters to better advise the public about these dangerous hazards.
locations of ocean rip currents
Locations of ocean rip currents

Courtesy of Fishing Piers

Courtesy of U.S Army Corps of Engineers Digital Visual Library

  • Piers, groins, and Jetties
  • River mouths or similar outlets
  • Near complex sandbar structures : intermediate beach types

Courtesy of Dennis Decker, WCM, NWS Melbourne, FL

Shepard et al. 1941, Wright and Short 1984


Beach Types

Wright and Short, 1984: Brander, 2012

shoreline structures ltb state
Shoreline structures + LTB state

Grand Haven, MI

Google Maps

river mouths or outlets rbt
River mouths or outlets + RBT…

Au Train, MI

Google Maps

what conditions were observed during rip current incidents on the great lakes
What Conditions Were Observed During Rip Current Incidents On The Great Lakes?
  • Wave Heights
  • Wave Periods
  • Wind Speed and Direction
wave height observations
Wave Height Observations

Waves between 2 and 4 feet

Sandbar incidents rare if waves less than 2 feet

wave height great lakes vs ocean
Wave height: Great Lakes Vs. Ocean
  • Higher waves on ocean made rip currents:
    • Less numerous
    • Stronger
  • Lower waves on ocean made rip currents:
    • More numerous
    • Weaker

Shepard et al. 1941; Shepard and Inman, 1951; Bowen, 1968

wave heights conclusions
Wave Heights: Conclusions
  • Life Threatening rip currents not likely if wave heights < 2 ft
    • Shoreline structures
    • River mouths
  • Threat increases once waves get to 2 ft
  • Forecasting Application:
    • Know your beach!
    • Always exceptions

Google maps

Park Point, MN frequently sees rip current incidents when waves are in the 1 to 3 ft range

wave period observations
Wave Period Observations

Short: 3 to 5 Seconds

wave period ocean
Wave period: Ocean
  • Long wave periods: Greater than 9 seconds
    • Larger volume of water onshore
    • Regularly spaced rip currents
    • Wide rip currents
  • Short wave periods: Less than 9 seconds
    • Numerous rip currents
    • Irregularly spaced rip currents
    • Smaller rip currents
    • Could contribute to duress of swimmer

Shepard et al. 1941, Shepard and Inman, 1951; Bowen, 1968

wind observations
Wind observations

Onshore or parallel to shore

winds indirectly related to rip current development
Winds: Indirectly related to rip current development
  • Lushine: Similar study on ocean in 1991
  • 100% cases onshore
  • 90% cases within 30 degrees of normal to shore
  • Wind speeds: 15 mph (6.7 m/s)
wind orientation to shore during g l incidents
Wind orientation to shore during G.L. incidents

Only 45% of onshore cases within 30 degrees of normal

forecasting application
Forecasting application
  • Onshore /Parallel winds: Rip Current Development
  • Know your beach!
  • Remember: Indirectly Related

Off Highway 2: Mackinac County, MI

Image Courtesy of Steve Hernek

synoptic pattern
Synoptic Pattern

Cold Frontal Passage

cold frontal passage
Cold frontal passage

August 16, 2010:

3 Fatalities

4 Rescues

cold frontal passage1
Cold frontal passage

August 1, 2009:

1 Fatality

8 Rescues

cold frontal passage2
Cold frontal passage

August 5-8, 2010:

7 Fatalities

5 Rescues

  • Forecasters: Know your beaches!
  • Suggestion: Collect your own data
  • In my study of the Great Lakes:
    • Most incidents were near shoreline structures
    • Wave heights 2 to 4 ft
    • Shore Parallel/Onshore Winds
    • Wave period 3 to 5 seconds
    • Cold front passage was common problem-pattern
questions comments


Ludington, MI. Photo by Megan Babich


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Bowen, A.J., and D.L. Inman., 1969: Rip currents, 2: Laboratory and field observations. Journal of Geophysical Research,74, 5479-5490

Brander, 2012. Science of the surf, 2012: SOS Fact Sheet: Beaches. [Available online at]

COMET, 2011: Rip Currents: Nearshore Fundamentals. []

Cook, D.O., 1970: The occurrence and geological work of rip currents off southern California. Marine Geology, 9, 173-186.

Dalrymple, R.A., 1975: A mechanism for rip current generation on an open coast. Journal of Geophysical Research, 80, 3485-3487.

Dalrymple, R.A., 1978: Rip currents and their causes. Proc. of the 16th International Conference of Coastal Engineering, Hamburg, American Society of Civil Engineers, 1414-1427.

Engle, J., J. MacMahan, R.J. Thieke, D.M. Hanes, R.G. Dean., 2002: Formulation of a rip current predictive index using rescue data. Proc. of the National Conference on Beach Preservation Technology, Biloxi, MS. Florida Shore and Beach Preservation Association.

Google, 2011: Google Maps. [Available online at]

Guenther, D., 2003: Rip current case study 3, 4 July 2003. Marquette Michigan National Weather Service Office Report.

Hite, M.P., 1925: The Undertow. Science, 62, 31-33.

Hydrometeorological Prediction Center, 2011: Hydrometeorological Prediction Center’s Surface Analysis Archive. [Available online at]

Hydrometeorological Prediction Center, 2011: The Daily Weather Map. [Available online at]

Lascody, R.L., 1998: East Central Florida rip current program. National Weather Digest, 22(2), 25-30.

Lushine, J.B., 1991: A study of rip current drownings and related weather factors. National Weather Digest, 16, 13-19.

Meadows, G., H. Purcell, D. Guenther, L. Meadows, R.E. Kinnunen, and G. Clark, 2011: Rip Currents in the Great Lakes: An Unfortunate Truth.Rip Currents: Beach Safety, Physical Oceanography, and Wave Modeling, S. Leatherman and J. Fletemeyer, Eds., CRC Press, 199-214.

McKenzie, R., 1958: Rip current systems. Journal of Geology, 66, 103-113.

Munk, W.H., 1949: The solitary wave theory and its application to surf problems. Ann. N.Y. Acad. Sci., 51, 376-424.

Nicholls, C.P.L., 1936: Rip Tides and How To Avoid Their Perils. Calif. Beaches Assoc., vol. 1 No. 9, 12.

Shepard, F.P., 1936: Undertow, rip tide or rip current. Science,84, 181-182.

Shepard, F.P., K.O. Emery, and E.C Lafond., 1941: Rip Currents: A process of geological importance. Journal of Geology, 49, 338-369.

Shepard, F.P., D.L. Inman., 1950: Nearshore circulation. Proc. of the 1st Conference on Coastal Engineering, Berkeley, CA, Council on Wave Research, 50-59.

Short, A.D., 1985: Rip current type, spacing and persistence, Narrabeen Beach, Australia. Marine Geology, 65, 47-71.

Sonu, C.J., 1972: Field observations of nearshore circulation and meandering currents. Journal of Geophysical Research, 77, 3232-3247.

Tang, E. and R.A. Dalrymple., 1989: Rip currents, nearshore circulation, and wave groups. In Nearshore Sediment Transport, R.J. Seymour, editor, New York, NY, Pelenum Press, 205-230.

Wood, W.L., and G.A. Meadows., 1975: Unsteadiness in longshore currents. Geophysical Research Letters, Vol 2, No 11.

Wright, L.D. and Short, A.D., 1984: Morphodynamic variability of the surf zones and beaches: A synthesis. Marine Geology, 56, 93-118.