GEOL118FinalExamFormat similartoexams1and2

Covers Lectures#27– 40 (GlobalClimateChangeI- MeteoriteImpactsIII)

8:00AM,Thursday,May11thLocationHEREBringPhotoID

OptionalQuestion/AnswerSessionLocationandtimeTBA

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#36FloodsIII- ProsandCons ofConstructionMeasuresforFloodControl

FloodControlUSandothercountrieshaveenormous"investment"inflood-proneareas (heavilyinhabitedanddeveloped),whichneedstobeprotected.Peoplehaveexpendedmanyresourcesto"control"flooding.

Trends in flood damage and cost of flood control measures, 1928 - 2006

FloodControl- ConstructionMeasuresFourmajorfloodcontrolmeasuresinvolvingconstructionare:channelization,floodways,dams,artificiallevees.

Fortified by a levee, a house near Vicksburg, MS survives Yazoo River flood in May 2011

FloodControl- ChannelizationChannelizationinvolveschangingchannelcharacteristicsincludingstraightening,deepening,orwideningchannel,orclearingdebrisfromthechannel,orliningchannelwithconcrete.Goalistoallowmorewatertobepassthroughriverwithfasterfloworgreaterdischarge.Sometimeschannelizationintendedforbothfloodcontrolandmeandererosioncontrol,importantforurbanrivers.

FloodControl- ChannelizationofBoneyard CreekBoneyard Creek,whichrunsthroughChampaign-Urbana,haditschannelenlarged,whichhelpedtoreduceflooding.

Channelized Boneyard Creek at Bardeen (Engineering) Quad

FloodControl- Floodway(DiversionChannel)transportsfloodwatersawayfrompopulatedareasExample=Winnipeg,Canada,built~30milefloodwayaroundcityin1968,whichgreatlyreducedfloodingfromRedRiver(floodwayloopsarounddevelopedregion,dumpswaterbackintoriverfartherdownstream)

Red River floodway

FloodControl- Dams/ReservoirsAdamblocksflowofriverandcreatesreservoirbehindit,usefulforfloodcontrolbecausereservoircanbefilledduringhighrainfallperiods.

Fanshawe Dam and Reservoir, England

Reservoirsusuallynotintendedtoretainallrainwaterduringflood;helptocontrolrateofstreamflow,likelargevalve.

FloodControl- RetentionPondRetentionpond(detentionbasin)isreservoironsmallerscaleforindividualtownsorneighborhoods.AnothersolutiontofrequentfloodingofBoneyard CreekwasconstructionoftworetentionpondsinareaboundedbyUniversityAve.,GreenSt.,SecondSt.,NeilSt.

Boneyard Creek detention basins

FloodControl- ArtificialLeveesArtificialleveesarehuman-madewallsofsandandmudbuiltalongsidesofchanneltoraiseheightofriverbank,allowinggreaterflowwithoutflooding.

artificial levee (grassy area) along Mississippi River

Topreventwaterseepagethroughlevee(weakensit),whichisbetter- sandormud?

mudleveeallowslesswaterseepagethroughbecausemudismuchlesspermeablethansand

ClickerQuestionTheleveebelowstopsfloodwatersfromgoingintothefloodplain.Howdoesthisaffecttheheightoffloodwatersdownstream fromthisarea,comparedtobeforetheleveeexisted?A. Tendstomakethefloodingworse.B. Tendstomakethefloodinglesssevere.C. Doesnotaffectdownstreamareas.

FloodControl- FloodwallsFloodwalls=concretelevees;muchmoreexpensivethansedimentlevees,mostcommonlyconstructednearcities,withhightaxrevenue

Floodwall along Mississippi River near St. Louis

Channelization,Floodway,Dam/Reservoir,ArtificialLeveeWhatarethebenefitstosociety(pros)associatedwiththeabovemeasures?

Whatarethedrawbackstosociety(cons)associatedwiththeabovemeasures?

FloodControl(Construction)Measures-Benefits,Drawbacks

Benefits

FloodControl(Construction)Measures- Benefits

FloodControlMeasure

ReduceFlooding(Decrease

Damage, Deaths)Channelization x

Floodway x

Dam/Reservoir x

Levee x

Meander,ErosionControl

x

x

Hydroelectricity,WaterSupply,Recreation

x

FloodControl- Dams/ReservoirsOtherbenefitstodamsandreservoirsincludehydroelectricity,watersupply,recreation

Hoover Dam along Colorado River

CanBeFutile(+ catastrophicfailure)

x

x

x

x

FloodControlMeasure Expensive

Channelization x

Floodway x

Dam/Reservoir x

Levee x

LimitedLifespan

x

x

x

x

FloodControl(Construction)Measures- Drawbacks

FloodControl(Construction)Measures- Drawbacks

FloodControlMeasure

FalseSenseofSecurity

Channelization x

Floodway x

Dam/Reservoir x

Levee x

LossofBeauty

x

x

x

x

FloodControlMeasure

TransfersProblemElsewhere

Channelization x

Floodway x

Dam/Reservoir

Levee x

CanWorsenErosionProblems

x

DrawbacksFloodControl(Construction)Measures- Drawbacks

FloodControl-Channelization

Kissimmee River, FL-channelized/straightened in 1960s, restored in 1980s

FloodControl- Channelization

Concrete-lined Los Angeles River

FloodControl- ChannelizationofBoneyard CreekBoneyard Creek,whichrunsthroughChampaign-Urbana,haditschannelenlarged,whichhelpedtoreduceflooding. Boneyard Creek-unscenic section

Boneyard Creek-scenic section

Crazy guy kayaking Boneyard

Impacts ofDams/Reservoirs

x

FloodControlMeasure

HabitatLoss(NegativeImpactonEcosystem)

Channelization x

Floodway x

Dam/Reservoir x

Levee x

Losefloodingbenefits(fertilesoil,water)

x

x

x

x

DrawbacksFloodControl(Construction)Measures- Drawbacks

DrawbacksofDams/ReservoirsOnedrawbackisthecreationofastandingwaterbody,whichcausesdepositionofsedimentinthereservoiranderosiondownstreamduetolackofsedimentload.

Deposition

ErosionInitial profile

Effect of Dam ConstructionDam

Therealsoisanimpactonecosystemduetochangefromrivertolakeecosystem(endangeredYangtzeRiverdolphin)

canalsohindermigrationoffishsuchassalmon

DrawbacksofDams/ReservoirsOtherdrawbackstodamsandreservoirsarelandlostandpeopledisplacedduetocreationoflargereservoirs,e.g.,ThreeGorgesDam,China,andlossofscenicbeauty

Lake Mead, associated with Hoover DamThree Gorges Dam, China

Puttingitalltogether….Makeaquicklistofthepositiveandnegativeimpactofalargedamproject.

OpinionQuestionInyouropinion,dodamsliketheThreeGorgesDamhaveanoverallpositiveimpact?A. Yes,positiveimpact.Morepositiveeffectsthannegative.B. No,overallnegativeimpact.Morenegativeeffectsthan

positive.C. Neutral- somepositive,somenegative,roughlyequal.