An examination of rip current incidents on the great lakes
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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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An Examination of Rip Current incidents on the Great Lakes

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An examination of rip current incidents on the great lakes

An Examination of Rip Current incidents on the Great Lakes

Megan Babich

NWS Marquette, MI


Overview

Overview

  • 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


Limitations

Limitations

  • 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


An examination of rip current incidents on the great lakes

Rip current fatalities and rescues on the Great Lakes 2002-2011


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.


Where do dangerous rip currents on the great lakes form

Where Do Dangerous Rip Currents On The Great Lakes Form?

Near Shoreline Structures!


Locations of ocean rip currents

Locations of ocean rip currents

Courtesy of NCbeaches.com: 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


An examination of rip current incidents on the great lakes

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


At beaches with only complex morphology tbr

At beaches with only complex morphology-TBR

Grand Marais, MI

Google Maps


An examination of rip current incidents on the great lakes

Most rip currents on the Great Lakes occur at beaches with shoreline structures!!!!!


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


An examination of rip current incidents on the great lakes

Total incidents used: 344/346


Why so many low height incidents

Why so many low-height incidents?


Why so many low wave height incidents

Why so many low wave height incidents?


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


Wave periods typically 3 5 seconds on the great lakes

Wave periods typically 3-5 seconds on the Great Lakes


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 s peeds during g l incidents

Wind speeds during G.L. incidents


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


Offshore winds possible explanations

Offshore winds: Possible explanations


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


Synoptic pattern1

Synoptic pattern


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


Popularity favorable conditions

Popularity + favorable conditions

PURE MICHIGAN


Conclusions

Conclusions

  • 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

Questions/Comments:

[email protected]

Website: http://www.crh.noaa.gov/mqt/?n=rip_toc

Ludington, MI. Photo by Megan Babich


References

References

Bowen, A.J., 1969: Rip currents, 1: Theoretical Investigations. Journal of Geophysical Research, 74, 5468-5478.

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 http://www.scienceofthesurf.com/downloads/SOSFact_Sheet_Beaches.pdf]

COMET, 2011: Rip Currents: Nearshore Fundamentals. [http://www.meted.ucar.edu/marine/ripcurrents/NSF/index.htm]

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 http://www.googlemaps.com]

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 http://www.hpc.ncep.noaa.gov/html/sfc_archive.shtml]

Hydrometeorological Prediction Center, 2011: The Daily Weather Map. [Available online at http://www.hpc.ncep.noaa.gov/dailywxmap/]

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.


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