Stream Transport: From Mountains to Oceans

11/18/2008Understanding EarthFifth EditionGrotzinger • Jordan • Press • SieverChapter 18:STREAM TRANSPORTFrom Mountains to OceansLecturer: H MohammadzadehAssistant professors,Department of Geology, FUMCopyright © 2007 by W. H. Freeman and CompanyChapter 18StreamTransport:FromMountains toOceans1

11/18/2008About Stream Transport• Streams and rivers are major geologicalagents of change in landscapes.• Streams are any flowing body of water,but rivers are major branches of a streamsystem.• Stream flow is related to the interactionof plate tectonic and climate systems.Lecture Outline1. Stream valley, channels, and floodplains2. Drainage networks3. How running water erodes solid rock4. How stream waters flow and transportsediment5. Deltas: the mouths of rivers6. Streams as geosystems2

11/18/20081. Stream valleys, channels, andfloodplainsThe three basic parts of a stream● valley (sloping area around thestream)● channel (bottom of valley)● floodplain (flat area in valleylevel with top of channel)Streamvalleys,channels,andfloodplains:incisedmeandersof theSan JuanRiver, Utah3

11/18/20081. Stream valleys, channels, and floodplains● Channel patterns● meanders (low sediment load,low velocity)● oxbow lakes● point bars and cut banks● braided streams (high sedimentload, high velocity)Streamvalleys,channels,andfloodplains:meanderingstreamsPoint barLow-velocity, low-sedimentstreams form meanders.Meanders shift from side toside in a snaking motion.The current is faster at outsidebanks, which are eroded.Sediments get deposited ininside banks forming pointbars.The bends grow closer andthe point bars bigger.During a major flood, theriver cuts across the loop.The abandoned loop remainsas an oxbow lake.4

11/18/2008Stream valleys, channels, and floodplains:a meandering river in Alaskapoint barStream valleys, channels, and floodplains:meanders of the Mississippi River5

11/18/2008Stream valleys, channels, and floodplains:braided streamslow-water water period(e.g., summer)Where high-velocity,high-sedimentstreams flowover easilyerodedterrain…Stream valleys, channels, and floodplains:braided streams…the water does notform oxbow bends…High-water period(e.g., spring snowmelt)…but cuts across theedges of existingchannels, creatingbraided channels.6

11/18/2008Stream valleys, channels, and floodplains:braided stream of the Chitina River, Alaskabraided channels1. Stream valleys, channels, andfloodplains● The stream floodplain● fine-grained sediment layers● agricultural resource● natural levees7

11/18/2008Stream floodplainsStreamvalleys,channels,andfloodplains:naturalleveesof theMississippidelta8

11/18/20082. Drainage networksThe drainagedivides andbasins2. Drainage networks: drainage networks9

11/18/20082. Drainage networks● Drainage patterns and geologichistory● antecedent streams● superposed streams2. Drainage networks:drainage patterns and geologic historyExample of an antecedent stream– the Delaware Water Gap,Pennsylvania-New Jersey10

11/18/20083. How running water erodes solid rockGullies and headward erosionPotholes11

11/18/20084. How stream waters flow and transportsediment: laminar and turbulent flow● Factors affecting laminar/turbulent● velocity, depth, and viscosity4. How stream waters flow and transportsediment: laminar and turbulent flow12

11/18/20084. How stream waters flow and transport sediment● Erosion and sediment transport● suspended load, ● bed load● Competence and capacity● velocity and volume of flow13

11/18/20084. How stream waters flow and transportsediment: settling of sediments14

11/18/20084. How stream waters flow and transportsediment: ripples and dunes4. How stream waters flow and transportsediment: ripples and dunes15

11/18/20085. Deltas: the mouths of rivers –delta sedimentation and bedding5. Deltas: the mouths of riversThe growthof deltas:theMississippiRiverdeltasedimentation16

11/18/20086. Streams as geosystemsGlaciersDendriticdrainageLakeWaterfallRapidsBraidedchannelMidstreamsandbarPoint barTerracedfloodplainMeanderingchannelCut bankOxbowlakeSwampand marshSubsidence occursin deltas.DistributarychannelWaterfallsdevelop whererocks resisterosion or wherefaulting offsetsthe streambed.Fine-grainedsedimentsof silt and clayGlaciersLakeAs the slopedecreases,rivers formbraided channels.NaturalleveeRapidsOlder sediments6. Streams as geosystemsRainfall and snowmelt gatherto create streams and rivers.DendriticdrainageIncisedbedrockWaterfallBraidedchannelMidstreamsandbarPoint barTerracedfloodplainMeanderingchannelSediments may be erodedto produce terraces.CoarsegrainedsedimentsSlopes are steep andonly the coarsest sedimentsare deposited.Cut bankMeandering channels form.Coarse-grained sedimentsare deposited.OxbowlakeFine-grainedsedimentsSubsidence occursin deltas.CoarsesedimentsCoarse depositsfrom older riversNatural levees maintainthe flow of water. Whenrivers flood, sedimentsare able to fillsurrounding areas.Swampand marshDistributarychannelThe current slows and depositsits fine sediments as a delta.17

11/18/20086. Streams as geosystems:Q = A x V1 m/s10 m3 mA river with lower cross-sectional sectional areaand velocity has a lower discharge…2 m/s9 m10 m…than a river with higher cross-sectional sectionalarea and velocity.18

11/18/2008Probability of occurrence (in any given year)Annual maximum discharge(m 3 /s)A large flood of 1800 m 3 /shas a probability of 10percent and a recurrenceinterval of about 12 years.Recurrence interval (years)Longitudinal Stream profileRivers are steepnear the head…● equilibrium of stream flow● topography (slope)● climate● streamflow (Q and V)● resistance of rock● sediment loadAltitude abovesea level (m)…and almost flatat the mouth.Distance from headwaters of river (km)SourceMouth19

11/18/2008● changes in base level (the quest for equilibrium)TIME 1A mature stream has developeda classic stream profile.TIME 3Sediment is now deposited in the lake.base levelTIME 2A change in base levels changesthe profile.TIME 4Eventually, the original stream profileis restored.newbase leveloldbase level6. Streams as geosystems● Places where streams adjustto changing conditions rapidly● alluvial fans● terraces20

11/18/2008Thelake -6. Streams as geosystemsin thisinstanceman-made,and itseffectKey terms and conceptsAlluvial fanAntecedent streamBase levelBed loadBottomset bedBraided streamCapacityChannelDeltaDendritic drainageDischargeDivideDrainage networkDuneFloodplainLaminar flowLongitudinal profileMeanderNatural leveeOxbow lakePoint barPotholeRippleRiverSaltationStreamSuperposed streamSuspended loadTerraceTopset bedTributaryTurbulent flowValley21