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A powerpoint on water movement and floods
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Water movement& Floods
Oncewaterhitstheground,wheredoeswatergo? Evaporatesintotheatmosphere Absorbedbyplants Soaksintotheground(intogroundwateraquifer)
Succumbstogravityandflowsdownhill
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Onland stepoftheHydrologicalCycle
Duringperiodsofnormalpercipitation,waterissoakedintothegroundandflowsintorivers/streams
Waterfollowsagradient toabaselevel (oceanorlake)
ConcernedaboutSurfaceRunoff Duringintenserainfall Waterflowsonsurfacetothestreams
Occursoveranentireareathatastreamdrains
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Watershed akadrainagebasin Theupstreamareafromwherewaterwillflowintoachannel
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Exist asfractals
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Rivershave afunctionoftransportingnotjustwater,butsolidsaswell boulders,sands,silts,muds
Thisisawaytodifferentiate theenergyofariver
LargeBoulders=
Highenergy,highvelocity
Fine Muds=
LowEnergy,Lowvelocity
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Duetovariationsinflowvelocity,riversformnaturallevees viadepositionofsedimentduringfloods
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Whenwateramountincreasesbeyondthenaturalcapacityofachannel,theriverhasenteredafloodstage
Floodsoccurasacrestmovingdownadrainagearea
http://water.weather.gov/ahps/
Apulseofwatermovingthroughasystem
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Duetowatershedarrangement,floodwatersfromasimilarareamayarrivetoariveratdifferenttimes
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Riseinfloodwaterscanoccuroveralongtimespandependantonwaterinputrate
Hourstoweeks(canassistwithpreparation)
Discussion:Urbanizationhasheightenedfloodintensity
Why?
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Flash Flood Occurssuddenlywithlittlewarningduetoasuddeninfluxofalargeamountofwaterintoadrainagearea Oftenoccurindry,desertareas(butnotlimitedto!) Havevarioussources/ causes(allresponsible forsuddenmassiveamountsofwater)
Meltwater Dam(naturalormanmade)failure
Thunderstorm
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Recurrenceinterval Theaveragetimebetweenfloodsofsimilarsize
Variesbyregionandriverdue toclimate,geography,andgeology
Thelarger theflood,thelongertherecurrenceinterval
A50yearfloodhasadischarge ofacertainamountandisestimatedtohappenevery50years
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CasestudyGreatfloodof1862 WestCoast, U.S.A.
IntenseRainNov61February 62(nonstoprainDec23Jan 22)
ColdstormsfollowedbyintensewarmstormfromthesouthinlateJanuaryFebruary
Largeamountofwater Strongstorm Snow melt
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1860CAstatepopulation 380,000(now38million+)
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Created inlandseas Orangecountyunder 4ftofwater
InlandEmpirecutinhalfbythousandsofacresofwatermileswide
Killed2040peopleinthisareaalone.Truenumberwillneverbeknown
ReroutedtheL.A.,SanGabriel,andSantaAnaRivers
Estimatedtobe5001,000yrflood
Casestudy
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Casestudy Sacramentounder10ftofwater(newgovernortookboattoinauguration)
200,000cattlekilled.ForcedCaliforniatoshiftfromranchingtofarmingeconomy
Overoftaxablepropertydestroyed.Beingreliantonpropertytaxes,thisbankruptedthestate
ChangedCaliforniaHistory
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YourvideodiscussionsheetsareduenextTuesday(10/8)at thebeginningofclass!
PlateTectonics
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