An Examination of Rip Current incidents on the Great Lakes

An Examination of Rip Current incidents on the Great Lakes

An Examination of Rip Current incidents on the Great LakesMegan BabichNWS Marquette, MIOverviewWhat 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?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.

Shepard et al. 1941Photo Courtesy of Don Rolfson, NWS MarquetteGrand Marais, MI: Lake Superior3How 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

4What causes these variations in stress?Differences in wave characteristics:HeightPeriodTidal influences/SeichesShoreline Structures

5The Great Lakes Current Incident Database346 current related incidents collected from media articles/eyewitness reports

Weather and lake conditions during incidents documented

2002-2011 swim seasons

LimitationsMedia coverage of incidents

Media assumptions and error

Limited observations of nearshore environment

Observations may not be representative of true environment

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)

Photo Courtesy of Univ. of Michigan Coastal Engineering Department Ludington, MI: Lake MichiganData from our database used to compute the average8Rip current fatalities and rescues on the Great Lakes 2002-2011Things to mention: Increase in deaths and Rescues over the years: Likely from increased media attention and increased availability of information. Overall, an average of about 10 fatalities per year. Total of 346 incidents in the database, 14 are channel currents.9Why 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?Near Shoreline Structures!

Locations of ocean rip currents

Shepard et al. 1941, Wright and Short 1984Courtesy of Dennis Decker, WCM, NWS Melbourne, FLCourtesy of NCbeaches.com: Fishing Piers Courtesy of U.S Army Corps of Engineers Digital Visual LibraryPiers, groins, and Jetties

River mouths or similar outlets

Near complex sandbar structures : intermediate beach typesShepard et al, 1941; Wright and Short, 1984. U.S. Army Corps of Engineers Digital Visual Library (river mouth).12Beach TypesWright and Short, 1984: Brander, 2012Shoreline structures + LTB state

Google MapsGrand Haven, MI

Longshore current intersects a breakwall. Grand Haven State Park, MI14River mouths or outlets + RBT

Google MapsAu Train, MI

Au Train River, Upper Michigan. 15At beaches with only complex morphology-TBR

Google MapsGrand Marais, MI

This beach is a transverse bar and rip state-one that most commonly sees rip current development. This is near Grand Marais, MI.16Most rip currents on the Great Lakes occur at beaches with shoreline structures!!!!!201/17What Conditions Were Observed During Rip Current Incidents On The Great Lakes?Wave HeightsWave PeriodsWind Speed and DirectionWave Height ObservationsWaves between 2 and 4 feetSandbar incidents rare if waves less than 2 feet

Wave height: Great Lakes Vs. OceanHigher waves on ocean made rip currents:Less numerousStronger

Lower waves on ocean made rip currents:More numerousWeaker

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

20Total incidents used: 344/346113/344 incidents were higher than the 2 to 4 feet range. 117/344 incidents were 3 feet or less. 113/344 were 2 to 4 feet.21Why so many low-height incidents?Reference: bring up the fact that rip currents can last more than 12 hours after conditions that generated them subsided. 25 total incidents with wave heights less than 25 ft22Why so many low wave height incidents?Total 1 to 3 ft cases: 92. 23Wave Heights: ConclusionsLife Threatening rip currents not likely if wave heights < 2 ftShoreline structuresRiver mouths

Threat increases once waves get to 2 ft

Forecasting Application: Know your beach!Always exceptions

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

Image: Googlemaps, satellite. Grand Marais, MI would be a second Example-only typically see dangerous rip currents when waves are greater than 4 ft.24Wave Period ObservationsShort: 3 to 5 SecondsWave period: OceanLong wave periods: Greater than 9 secondsLarger volume of water onshoreRegularly spaced rip currentsWide rip currentsShort wave periods: Less than 9 secondsNumerous rip currentsIrregularly spaced rip currentsSmaller rip currentsCould contribute to duress of swimmer

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

26Wave periods typically 3-5 seconds on the Great LakesDue to the fact that waves are primarily wind waves, versus swell on the ocean. Would imply more numerous and smaller rip currents, however this was not directly observed. May add to the distress of swimmers caught in the current, with wave-current combination. 27Wind observationsOnshore or parallel to shoreWinds: Indirectly related to rip current developmentLushine: Similar study on ocean in 1991100% cases onshore90% cases within 30 degrees of normal to shoreWind speeds: 15 mph (6.7 m/s)

Wind speeds during G.L. incidentsConsistent with Lushines findings: most commonly observed speed was between 10 and 20 mph (4.5 to 8.9 m/s).30Wind orientation to shore during G.L. incidentsOnly 45% of onshore cases within 30 degrees of normal344/346 cases used in the total. Parallel winds account for some of the channel current cases and structural rip current cases.31Offshore winds: Possible explanationsThunderstorm activity: Measurement device (winds or waves) could be unrepresentative of the environment. Also, seiche activity could have been occurring but measurement equipment was not in place. There was only 6 incidents with offshore winds, and they occurred on the same day. Could be example of unrepresentative data.32Forecasting applicationOnshore /Parallel winds: Rip Current Development Know your beach!

Remember: Indirectly Related

Image Courtesy of Steve HernekOff Highway 2: Mackinac County, MIOff Highway 2, Mackinac County, MI. Courtesy of Steve Hernek

33Synoptic PatternCold Frontal PassageSynoptic patternCold frontal passage

August 16, 2010: 3 Fatalities4 RescuesAugust 16, 2010. 3 deaths, 4 rescues. One was in Berrien County (Lake MI), the other was in Kincardine, Ontario (Lake Huron), and the final was at Rock Pointe Provincial Park, Ontario (Lake Erie)36Cold frontal passage

August 1, 2009:1 Fatality8 Rescues3 rescues at Grand Haven Pier, 1 drowning and 5 rescues at South Haven Pier37Cold frontal passage

August 5-8, 2010: 7 Fatalities5 Rescues2 deaths at Middle Bay (Marquette, MI), 2 deaths at Grand Marais, MI, 2 deaths in Van Buren County (Lake MI). The next day, when conditions were subsiding, there were 3 rescues at Au Train, MI. Across Lake Erie, the mayhem continuedwith 1 drowning and 2 rescues. 38

39Popularity + favorable conditions

PURE MICHIGANPure Michigan website map of Michigans featured beach towns (right). Counties in red indicate areas with the most rip current incidents (right) from the database.40ConclusionsForecasters: Know your beaches!Suggestion: Collect your own dataIn my study of the Great Lakes:Most incidents were near shoreline structuresWave heights 2 to 4 ftShore Parallel/Onshore WindsWave period 3 to 5 secondsCold front passage was common problem-pattern

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Website: http://www.crh.noaa.gov/mqt/?n=rip_tocQuestions/Comments:Ludington, MI. Photo by Megan Babich42ReferencesBowen, 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, 5479-5490Brander, 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 Centers 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.