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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