River Features - DEVELOPMENT
Transcript of River Features - DEVELOPMENT
Eddies• Aneddyisanareaofswirlingwaterthatformsbehindanobstaclelikeaboulderinariver.
• Oftenthewaterintheeddywillreversethedirectionofflowandwillflowupstream.
• Eddiesarealmostalwaysformedontheinsideofthecornerwhenariverturnsacorner.
• Theareawherethedownstreamcurrentmeetstheeddyiscalledaneddyline.Theeddylinemixesthewaterflowinanunpredictableway.
• Tocrosstheeddylinerequiressomeeffort.Kayakerscancrossaneddylineeasilywhileswimmersmustswimhardandusealotofenergytocrosstheeddyline.
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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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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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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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FactSheetStandingwaves
Animation showing standing waves
Standing waves in the river
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FactSheetRapids
Rapids Rapids
RapidsRapidsarestretchesofwaterwherethewaterflowhasbeendisruptedandbecomesturbulent.Thesizeandturbulenceofarapiddependson:
• thesteepnessoftheriver
• thenumberandsizeofobjectslikerocksthatblocktheflowofthewater
• thevolumeofwaterflowingdowntheriver.
Swimmerscanbeinjuredwhentheyarepushedagainstrocksbythecurrentorflowofthewater.Thewhitewaterintherapidsisaeratedorfullofairbubblesandisnotverybuoyantsoitdoesnotsupportaswimmeraswellasnormalwater.
Waterfalls• Riverscanfallinheightquitequicklywhenthewaterflowsoverwaterfalls.
• Waterfallscanbedifficulttoseefromupstreambuttheycanbeeasiertohearthanotherhazards.
• Manywaterfallshaveastrongrecirculatingwaveattheirbaseandanareaofaeratedwater.Peoplecangettrappedatthebaseofawaterfallanddrown.
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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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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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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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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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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
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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