Eddies• Aneddyisanareaofswirlingwaterthatformsbehindanobstaclelikeaboulderinariver.

• Oftenthewaterintheeddywillreversethedirectionofflowandwillflowupstream.

• Eddiesarealmostalwaysformedontheinsideofthecornerwhenariverturnsacorner.

• Theareawherethedownstreamcurrentmeetstheeddyiscalledaneddyline.Theeddylinemixesthewaterflowinanunpredictableway.

• Tocrosstheeddylinerequiressomeeffort.Kayakerscancrossaneddylineeasilywhileswimmersmustswimhardandusealotofenergytocrosstheeddyline.

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Be River SafeRiverFeatures

FactSheetEddies

Animation of water flow around the rockRock in river showing eddy

EDDY

Recirculating waves• Recirculatingwavesareformedimmediatelydownstreamoflargeobjectslikerocks.

• Arecirculatingwaveiswherethewatercontinuallyflowsbackoveritself.Objectsincludingpeoplecanbeheldortrappedinrecirculatingwaves.

• Recirculatingwavesarecreatedwhenthedownstreamdropinwaterlevelisofasignificantsize.

• Recirculatingwavesarealwaysbreakingandcontainwhite,aeratedwater.

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Be River SafeRiverFeatures

FactSheetRecirculatingwaves

Submerged rock in river showing recirculating waves Animation of water flow over and around a submerged rock

Cross section diagram showing recirculating wave

Buffer waves• Bufferwavesareformedwhentheriverflowsintoanobstacle.Thebufferwaveisupstreamof

theobstacle.

• Themorewaterhittingtheobstacle,thebiggerthebufferwave.

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Be River SafeRiverFeatures

FactSheetBufferwaves

Rock in river showing buffer wave

Cross section diagram showing buffer wave

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Animation of water flow over and around the rock

Standing waves• Awaveisformeddownstreamofasubmergedobstaclelikearock,ordownstreamfromwhere

arivernarrowsabruptly.Dependingonthesizeoftheobstacleorrockthereisusuallymorethanoneofthesewaves.Theyarecalledstandingwaves.

• Wavescanbreakoverswimmers,pushingthemunderthesurface.

• Standingwavesmaybebreakingorsmooth.

• Standingwavesstayatthesameplaceintheriver.

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Be River SafeRiverFeatures

FactSheetStandingwaves

Animation showing standing waves

Standing waves in the river

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Be River SafeRiverFeatures

FactSheetRapids

Rapids Rapids

RapidsRapidsarestretchesofwaterwherethewaterflowhasbeendisruptedandbecomesturbulent.Thesizeandturbulenceofarapiddependson:

• thesteepnessoftheriver

• thenumberandsizeofobjectslikerocksthatblocktheflowofthewater

• thevolumeofwaterflowingdowntheriver.

Swimmerscanbeinjuredwhentheyarepushedagainstrocksbythecurrentorflowofthewater.Thewhitewaterintherapidsisaeratedorfullofairbubblesandisnotverybuoyantsoitdoesnotsupportaswimmeraswellasnormalwater.

Waterfalls• Riverscanfallinheightquitequicklywhenthewaterflowsoverwaterfalls.

• Waterfallscanbedifficulttoseefromupstreambuttheycanbeeasiertohearthanotherhazards.

• Manywaterfallshaveastrongrecirculatingwaveattheirbaseandanareaofaeratedwater.Peoplecangettrappedatthebaseofawaterfallanddrown.

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Be River SafeRiverFeatures

FactSheetWaterfalls

Cross section diagram showing recirculating wave at the base of the waterfall

Waterfalls

Obstacles• Anobstacleisanobjectthatstandsintheflowoftheriver,forcingthewatertoflowaroundit.

• Obstaclescanbeman-madeconstructionslikebridgesupports,orthingslikeboulders,treetrunksandprojectinglandmasseslikebluffs.

• Swimmerscanbepushedorcarriedintoobstaclesbytheflowofthewater.Theycanbeinjuredbytheforceofthecollisionwiththeobstacle.

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Be River SafeRiverFeatures

FactSheetObstacles

Tree roots forming an obstacle The bluff is an obstacle to the flow of the river

Rock and debris forming an obstacle in the riverConstruction debris forming an obstacle in the river

Strainers• Astrainerisanobstacleintheriverthatallowswatertoflowthroughitbutstopslargersolid

obstacles.

• Strainersaretypically:

- treebranchesorrootsheldintheriveracrossthecurrent

- fences

- constructiondebrislikereinforcedsteelmesh

- collectionsofboulders.

• Strainersmaybevisibleorfullysubmerged.

• Swimmerscanbetrappedagainststrainersbytheforceoftheriverflow.Theycannotgetfreeanddrown.

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Be River SafeRiverFeatures

FactSheetStrainers

The log caught between two rocks acts as a strainerA fence across a stream acts as a strainer

A constructed strainer

River users may not see this strainer until they are close to it

Weirs• Man-madefeatureslikedamsandweirsareparticularlydangerousastheyspanthefullwidthof

theriverorwaterway.Thereisnoopportunitytomoveawayfromthem.

• Thisweirshowsastrongrecirculatingwave.

• Donotswim,kayakorcrossarivernearaweiroradam.

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Be River SafeRiverFeatures

FactSheetWeirs

Weirs extend across the full width of the river

A weir with animation showing the flow of water over the river

Unstable or undercut banks• Theforceofthewaterflowingdownariverconstantlyerodesorwearsawayitsbanks.

• Banks,wheretheforceofthewateriswearingawaylandatwaterlevel,becomeundercutorunstable.Thesebankslookstabletopeoplewalkingontopofthembuttheymaybereadytocollapse.

• Peoplestandingonariverbankorwalkingbesidearivercanfallinwhenanundercutbankcollapsesintotheriver.

• Anunstableorundercutbankcanalsocollapseifaswimmertriestoclimboutoftheriverontoit.

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Be River SafeRiverFeatures

FactSheetUnstableorundercutbanks

An unstable or undercut bank

An example of where the water is wearing away land and forming an undercut bank

The force of the water is causing this river bank to become unstable

Be River SafeRiverFeatures

FactSheetThenatureoftheriverbottom

The nature of the river bottomThespeedofthecurrentprovidesanindicationofthenatureofthebottom.

Riverbedscanhaveashinglebedorbemuddy,sandyorsilty.

Theriverbottommaybeevenormaycontaindeepholesandshallowareas.

Insomeriversitiseasytoseethenatureoftheriverbed;inotherscloudyordirtywatercanmakeithardtoseetheriverbottom.

Theriverbanksmaygivegoodcluesaboutthenatureoftheriverbottom.

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River showing the nature of the river bottom

River showing the nature of the river bottom

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Cross section diagram showing the nature of the river bottom