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Human impacts on riversSlide Number 2Slide Number 3ChannelizationChannelizationHuman impacts on riversHuman impacts on riversHydraulic MiningHydraulic MiningSacramento river bed elevations 1850-1910Rising river bed exacerbates flooding on Sacramento River beginning in 1860sSacramento river bed elevations 1850-1910Sacramento and Yuba river bed elevations 1850-1950Sedimentation in San Francisco Bay delta / estuaryHydraulic Mining and Dam ConstructionDeclining sedimentation in San Francisco Bay delta / estuary due to passing of sediment wave and dam constructionPost mining levees and subsidence in Sacramento River deltaFlooding on Sacramento RiverHuman impacts on riversGreen River, WashingtonWater Extensive floodplain development from 1961-2009Howard Hanson DamGreen River “flood protection”Green River “flood protection”Howard Hanson dam started leaking almost as soon as it was finishedAnatomy of Howard Hanson DamInside the dam’s drainage tunnelPotential Internal ErosionHow to fix the dam?Green River “flood protection”Green River Valley FloodingSlide Number 331965 Flooding Along East Valley HighwaySlide Number 35Slide Number 36Slide Number 37“Supersacks” as flood protection Supersacks add a bit of height to the leveesGreen River Valley FloodingGreen River Valley FloodingInteractions between land use and "increased flood damage" in a watershedHuman impacts on riversWaterSedimentWoodclimatecatchment vegetationchannel morphologychannel morphologygeologygeologygradientgradientvalley formvalley formhydrologyhydrologyriparianveg.riparianveg.sediment& wood inputs sediment& wood inputsflowobstructionsflowobstructionsfastslowrate of changeclimatecatchment vegetationchannel morphologychannel morphologygeologygeologygradientgradientvalley formvalley formhydrologyhydrologyriparianveg.riparianveg.sediment& wood inputs sediment& wood inputsflowobstructionsflowobstructionsfastslowrate of changeChannelization = direct human interventionChannelizationLos Angeles RiverChannelizationIllabot CreekSkagit River WatershedHuman impacts on riversWaterSedimentWoodHuman impacts on riversGlobally, we have increased upland erosion by about ten times, while simultaneously cutting sediment delivery to oceans by half…Hydraulic MiningSierra NevadaHydraulic MiningSierra Nevada, Yuba County, 1870Sacramento river bed elevations 1850‐ 1910Rising river bed exacerbates flooding on Sacramento River beginning in 1860sK Street, looking east, 1862Sacramento river bed elevations 1850‐ 1910Farmers get mad and outlaw hydraulic miningHydraulic miningHydraulic miningHalf century lag time to move sediment through system…Sacramento and Yuba river bed elevations 1850‐1950Sedimentation in San Francisco Bay delta / estuary• 40% of SF Bay filled in with mud• 1.5 billion yards of sediment (8 times the amount excavated to build the Panama Canal)Hydraulic Mining and Dam ConstructionSan Francisco Bay watershedDeclining sedimentation in San Francisco Bay delta / estuary due to passing of sediment wave and dam constructionSan Pablo Bay / San Francisco BayPost mining levees and subsidence in Sacramento River delta> 20 ftFlooding on Sacramento River20041997Human impacts on riversWaterSedimentWoodGreen River, WashingtonWater Dam built for downstream “flood control”Extensive floodplain development from 1961‐ 2009Howard Hanson DamGreen River “flood protection”• Flood control plans on the Green River depended upon maintenance of the dam;• Dam operations limited the flow in the river to < 12,000 cfs for most years, equal to pre‐dam 2 yr recurrence interval flow;• With dam in place the 2 yr, 100 yr, and 500 yr floods were all determined to be = 12,000 cfs.Green River “flood protection”• Control of overbank flows led to the “promise” of no more valley bottom flooding …and so the floodplain land values skyrocketed and commercial and residential development replaced farms on most of the valley bottom.• But…Howard Hanson dam started leaking almost as soon as it was finishedTwo depressions formed in right abutmentRightAbutmentEmbankmentFlood ControlTowerFish PassageFacility ExcavationSpillwayGreen RiverEagle GorgeReservoirBig DepressionLocationEngineeredFilter BlanketDrainageTunnelLandslideDebrisSmall DepressionLocationExistingGroutCurtainAnatomy of Howard Hanson DamInside the dam’s drainage tunnelNormally, dye placed in the reservoir seeps through in 12 hours; it’s now happening in < 2 hours… Normally, dye placed in the reservoir seeps through in 12 hours; it’s now happening in < 2 hours…Potential Internal Erosion• Grout curtain and additional wells, November 2009• Cutoff wall, FutureHow to fix the dam?Green River “flood protection”• To fix the dam will require time as the reservoir is drawn down and can store less water; • With dam unable to store the equivalent of a several year RI flood, let alone a 500 yr flood, what is the prognosis for the levees being able to contain floodwaters?• Extensive annual flooding along valley bottom• “Pre‐development” flood extent in 1965; after the dam was in place!• Natural levees along the river built up to contain the bankfull flow (12,000 cfs)Green River Valley Flooding1965 Flooding Along East Valley Highway1965 Flooding Along East Valley Highway13,900 cfs17,600 cfs25,000 cfs“Supersacks” as flood protection Supersacks add a bit of height to the levees• Other styles of “flood control” include getting infrastructure out of harms way, levee setbacks, and designing “floodways” along which flood flows would be routed…• For this year, there are not many options other than to warn the public, set up a flood warning system, “enhance” the levees, and pray it doesn’t rain a lot…Green River Valley Flooding• FEMA estimates that flooding from a levee breach at ≈ 12,000 cfs could displace 15,000 to 20,000 people and cause $1.3 to 3.7 billion in damage.• How does flood control affect flood risks?Green River Valley FloodingInteractions between land use and "increased flood damage" in a


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UW ESS 230 - Water Sediment

Documents in this Course
Soils

Soils

36 pages

Erosion

Erosion

37 pages

Soils

Soils

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Erosion

Erosion

34 pages

Rivers

Rivers

42 pages

Soils

Soils

37 pages

Soils

Soils

36 pages

Erosion

Erosion

35 pages

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