RipCurrentsandRipCurrent
Hazards
RobinDavidson-Arnott
DepartmentofGeography
UniversityofGuelph
Outline
*  Introduction
*  Ripcurrentsandundertow
*  Ripcurrentsonopenbeaches
*  RipcurrentsintheGreatlakes
*  Ripcurrenthazards
*  Addressingthehazard
*  Discussion
Introduction
RipHead
Breakerzone
Rip
Current
Longshorecurrent
*  Standardtextbookdepictionofripcurrentsshowswave
breakingoffshoregeneratinglongshorecurrentsinthesurf
zone,convergingtoproduceafast-flowingripcurrent
flowingoffshoreanddissipatingbeyondthebreakerline.
Introduction-BarsandRips
*  Ripcurrentsarealsoassociatedwithsandbars.Wavesbreakonthebar
andthelongshorecurrentsflowinthetroughlandwardofit.Thefastflowingripcurrentsexcavateachannelwhichcutsthroughthebar.Left
photoshowsmoderatewavesbreakingonbarsatGreenwichDunes,
PEI.Rightphotoisatimelapse.Whiteareasarewherewavesare
breaking-primarilyonaninnerbarwithsomeonabarjustseaward.
Darkareasarethetroughlandwardofthebarsandtheripchannels.A
prominentripchannelcanbeseentowardsthetoprightofthephoto.
Introduction-BarsandRips
ComplexbarandripsystemsonthewestcoastofFrance.Takenfrom:
Modellingthealongshorevariabilityofoptimumripcurrentescape
strategiesonamultiplerip-channelledbeach.(Biscarrosse,SWFrance).
BrunoCastelle,R.JakMcCarroll,RobertW.Brander,TimothyScott,BenjaminDubarbier.
NaturalHazards,2016.
RipCurrentsandUndertow
*  RipCurrentsandundertowarebothaformofreturnflow
*  Inthelakewaterparticlestraceacircularmotionasthe
wavegoesbybutthereislittlenetmovementofthewater
*  Whenawavebreaksamassofwatermovesforwardinto
thesurfzonetowardsthebeach–asmorewavesbreak
thecontinuedinjectionofwaterraisesthewaterlevel
closetothebeach=set-up
*  Theheadofwaterclosetothebeachthenforceswater
offshoreasundertowand/orripcurrentsuntiltherateof
offshoreflowequalstherateofonshoreflowinthe
breakingwaves
Undertow
v  Undertowtakesplaceuniformlyalongshoreandisconfinedtothelower
halfofthewatercolumn–flownearthesurfaceisonshore
v  Becauseflowisuniformalongshoreflowspeedsaresmall-<15cm/sec
v  Nearshoresandbarsarestraightandtherearenoripchannels
v  slowspeed,locationawayfromthesurfaceandabsenceofchannels
meansafeforswimmers
v  e.g.WasagaBeach,SaubleBeach
RipCurrents
v Ripcurrentfoundatspecificlocationsandoffshore
flowextendsrighttothesurfaceeveninbreaking
waves
v Becauseoffshoreflowisconfinedtonarrowzones
speedsarelarge0.5to1.5m/sec
v Nearshoresandbarsareobliqueorcrescenticand
associatedwithdeeperchannelswhichcutthroughthe
bar
v Fastcurrentandpresenceofchannelsmeandangerous
forswimmers
v e.g.GreatLakes?California,Australia,westcoast
France,Brazil
SurfersandRipCurrents
Muchoftheresearchcarriedoutonripcurrenthasbeenstimulatedby
reportsfromsurfers,particularlyinAustraliawhereSurferLifeguard
Societiesarefoundinmanyareas
RipCurrentsintheGreatlakes
*  Ripcurrentdevelopbestontheopencoastwithlarge
wavesandespeciallylargeswellwavesthatbringalotof
waterintothesurfzone
*  Theyareoftenpresentevenonadaywithlittlewind
*  IntheGreatLakeslargewavesarealwaysassociatedwith
strongwindsduringastormandswellwavesareonly
presentforafewhoursaftertheevent.
*  Mostpeopledonotgoswimmingduringsuchanevent–
exceptionbeingsurfers,windsurfers.So,ifripcurrentsare
generatedtheygounnoticed
RipCurrentsintheGreatlakes
*  Ittendstogetignoredinthebigsurfingareas,butonshore
winds,andparticularlywindsblowingatabitofanangletothe
shoreline,canalsogeneratestronglongshorecurrentsevenif
thewavesarerelativelysmall–say0.5-0.75m.
*  Windsblowingobliquelyalongshoredragthewatersurfaceand
inshallowwateralongshorecurrentissetupthatisaidedby
waterandenergyfromthebreakingwaves.
*  Becausethebarandtrougharegenerallyshallowandeasily
wadeablenoonepaysmuchattentiontothecurrentandthe
wavesarejustbigenoughforthemtobeperceivedas
somethingtoplayin–notadangerouscondition.
*  Theproblemariseswhenthecurrentflowingalongshore
encountersanobstaclesuchasanaturalheadlandorjetty.
HeadlandRips
*  Thepositionofripchannelsontheopencoastchangeswithtime
andmayvaryfromstormtostorm.
*  Ithaslongbeenrecognisedthatwherethereareheadlands
whichformabarriertothealongshoreflowofwater‘permanent’
ripchannelsmaybeformedandripcurrentswillbeformedthere
allthetimeunderaparticularsetofconditions.
*  MostdrowningsintheOntarioGreatLakesappeartobe
associatedwithheadlandrips–eitheratanaturalheadlandor
wherethereisanartificialbarriersuchasthejetties/breakwater
attheentrancetosmallharbours
Pt.AbinoHeadland
*  IInvestigatedtheconditionsatPt.Abino,NEshoreofLakeErie,with
respecttotwodrowningsthatoccurredthere
*  Inbothcaseschildrenoninflatableraftswerebeingcarriedlakewardin
thecurrent.Theysurvivedbuttheirrescuer(parent)drowned
Left:vieweasttowardsthelimestoneheadlandofPointAbino-arrowmarks
darkareaofripchannel.Insetisclosupshowingsandbarendingatheadland.
Rightissurveyedcrosssection.Waterinthechannelistoodeeptostand
Pt.AbinoRipCurrentFormation
EarlyAfternoon
LateAfternoon
*  Inthesummerwarmsunnydaysoftenassociatedwiththedevelopmentof
SWwindswhichblowobliquelyonshoreatPt.Abino
*  Asinlandheatsupduringthedaywindsgetstrongerandwavesbeginto
buildinsize
*  Longshorecurrentgeneratedflowingtowardsthepointoncrestorjust
landwardofcrestofbar.Largerwavesmaybegintobreakonthebar
Pt.AbinoHeadland
winds
waves
SWwindsandwavesgeneratealongshorecurrentflowingtowardsthe
headlandwhichisdeflectedoffshorethroughtheripchannel.
HarbourBreakwater
Harbourjettiesactasaformofheadland
HazardsofRipCurrents
*  Theyflowfasterthantheaverageswimmercanswimagainstand
fasterthanagoodswimmercanmaintainformorethanafew
tensofseconds
*  Theycarryyouawayfromshoreintoanareaofdeeperwater
*  Theymaycarryyouintoazonewithhigherwaves
*  Inthewateryougenerallycannotseetheextentoftheripcell
*  Aheadlandripcurrentmaycarryyouontodangerousrocksora
verticalharbourbreakwallthatoffersnopurchase
*  Yougettired,coldandyoumaydrown
AddressingtheHazardsofRip
Currents
*  Threegroupsofpeopleinvolvedinaddressingthehazards
1.  Theswimmerorswimmers
2.  Peopleinthevicinity–therescuers
3.  Peopleinauthority–beachmanagers,lifeguardtraining,
firstresponders;variouslevelsofgovernment
*  Whathavewelearntthatmaybehelpful?
*  Thereisalargebodyofliteratureonallthree–inparticular
fromtheUS,Australia
AddressingtheHazard
TheSwimmer
*  Readthesigns,beawareandavoidareaswheretheripcurrent
maydevelop
*  Parentsbeawarethatwindsmaytakeyourchildintotheareaof
stronglongshorecurrentsandripcurrents,especiallyiftheyare
onsomeformofflotationdevice
*  Ifyoufindyourselfinaripcurrentdonotswimagainstthe
currentunlessyouareonlyafewmetresfromshallowwater
whereyoucanstandorfromsomethingyoucangrabholdof
*  Letpeopleonthebeachandaroundknowyouthatyouarein
trouble–shoutforhelp!
*  Decidewhatisthebestcourseofactiontosaveyourself
TheSwimmer
StrategiesforSavingYourself
*  Whatareyourchoices?
*  Swimtosafety–whatdirection?Onshore,offshore,
alongshoredownwind;alongshoreupwind.Whichisthe
best?
*  Oldadvice–don’tswimonshoreagainstthecurrent,swim
alongshoreandthencomeashorewiththewaves
Simpleflow
opencoast
rip
Complexflow
opencoast
rip
TheSwimmer
StrategiesforSavingYourself
v  Lastdecadenumberofstudies
evaluatingripcurrentescape
strategiesusingdrifterswithGPS
andtrackinghumansubjects
v  Allshowcomplexityofripcell
circulationandthatnosingle
escapeactionsucceedsallthetime
v  Swimmersareallexperienced
surfers
McCarrolletal.,2014.Evaluationof
swimmer-basedripcurrentescape
Strategies.NaturalHazards,71,1821-1846
TheSwimmer
StrategiesforSavingYourself
*
*
*
*
*
Whatisbestforripsatheadlandsandjetties?
Swimalongshoreupwindandthenonshorecanbesuccessful
Difficultagainstwindandwavesunlessyouareastrongswimmer
Swimdownwindonlyifyoucanreachshoreorclimbjetty
Inmostcasesfloatandletyourselfbecarriedoffshorebythecurrentis
safest.Turnsoyouarefacingshoreandawayfromwindandwaves
AddressingtheHazard
TheRescuers
*  Immediatelyletotherpeopleknow–andcall911
*  Donotattempttorescueunlessyoucanstandorareavery
strongswimmer
*  Attemptifpossibletogetsomeformofflotationdeviceor
buoyantobjecttothepersonintrouble–life-savingring;life
jacket;boogieboard;inflatableraft
*  Attractattentionofanywatercraftnearbytocarryoutrescue
*  Keeppersoninsightinordertodirectrescuers
*  Workwithotherstocarryoutallthesetasksuntilfirstresponders
arrive.
AddressingtheHazard
TheAuthorities
*  Rangeofstrategiesthatlocalandprovincialauthoritiescanaddress.
*  Lifeguardandlifeguardtraining
*  Warningsignsonbeachandonjetty.Informationsignsforwhattodoif
youaretheswimmerandtherescuer.Thesecouldbecreated
provinciallyandgivenfreetoallmunicipalitieswithbeachesonthe
GreatLakes
*  Flotationdevicessuitableforaidingtheswimmerindifficulty.Shouldbe
easytodeployandavailableinseverallocations
*  Programmesatthestartofthesummertoeducatebeachgoersastorip
hazardsandwhattodo.Focusonfamilieswithyoungchildren
*  Co-ordinationandtrainingoflocalmarinaoperators,firstresponders
etc.
*  Andmanyotherpossibilities
YouTubeVideos
*  LotsofvideosonYouTube–3youmighttryare:
*  Dr.Beach:RipCurrents(Dr.SteveLeatherman)
*  RipCurrents–SurfLifeSavingatUNSW(UniversityofNew
SouthWales,Sydney,Australia)feturingDr.RobBrander–
AKADr.Rip
*  RipCurrents–thehiddenDanger.ParksCanada