STREAM SYSTEMSand FLOODS• Precipitation• Evaporation• Infiltration• Runoff• TranspirationEarth’s Water and the Hydrologic CycleThe Hydrologic CycleThe Hydrologic Cycle• Oceans not filling up• Evaporation = precipitation• System is balanced• Runoff is the streamsEarth’s Water and the Hydrologic CycleThe Hydrologic CycleRUNNING WATER• Comes from precipitation• Transports sediment• Erode channelsDRAINAGE BASIN• Area that drains into a stream• Separated by drainage divides• Tributaries contribute water to trunk streamWillamette Basin• http://blog.oregonlive.com/breakingnews/2008/02/large_willamette.gifTHE WORK OF STREAMS•Erosion • Transportation• DepositionEROSION• Lifting loose particles• Abrasion• Dissolution• Depends on velocity– Gradient– Channel characteristics– DischargeCONTROLS OF EROSION• Slope of channel• Vertical drop / channel lengthGRADIENTStream Gradient• Slope of channel along length of stream• Changes from head to mouth of stream• Shape•Size• Roughness• GradientCHANNEL CHARACTERISTICS• Same cross sectional area• Channel perimeter about doubledCHANNEL SHAPE• Volume of water flowing past a point in a certain amount of time• Increases downstream• Cross sectional area x velocity• Gaging stationDISCHARGEGAGING STATIONDISCHARGE CALCULATION• http://www.waterwatch.org.au/library/module-4/flow.html#10Willamette Discharge Winter 2006• http://waterdata.usgs.gov/or/nwis/uv?format=gif&period=31&site_no=14191000FLOODS• River rises above normal bank retainment• Described as ‘Flood Stage’• Measured in feet above bank full discharge• Floods occur periodically—due to weather variations– Rainfall– Snowmelt– Uncommon events like landslide or lava damsWillamette Valley 1996• http://www.bpa.gov/Power/pl/columbia/4-gal-2.htmLake Oswego 1996• http://www.ci.oswego.or.us/engineer/images/Copyof96-flood-03_000.jpgWillamette Flood• http://zebu.uoregon.edu/flood3.htmlRECURRENCE INTERVAL• 100 year flood—1% chance of occurrence in a given year• 20 year flood—5% chance• 500 year flood—0.02% chanceTypes of Floods• Riverine floods– Slow events from protracted rainfall– Fast events from sudden rainfall• Coastal floods– Storm surge–High tide– rainfall• Catastrophic floodsFlood effects• Infrastructure damage•Disease• Crop and food supply• Natural vegetationFlood Control• Containment• Water management• Flood-plain building restrictionsLevees• Pink is levees•Brown is hilllines• http://www.mvd.usace.army.mil/mrc/mrt/index.phpDams• http://www.bpa.gov/corporate/bpanews/library/images/dams/descriptions/detroit.cfmFlood zone• http://en.tourduvalat.org/nos_programmes/observatoires_biodiversite_et_politiques_publiques/observatoire_des_zones_humides_mediterraneennesFloodplain building plan• http://www.australianecosystems.com.au/projects-edgewater-estate.htmSUMMARY OF CHANGES FROM HEAD TO MOUTH OF STREAM• Channel gradient• Channel size• Discharge• Velocity of flow—controlled by– Gradient– Channel shape– DischargeTHE WORK OF STREAMS•Erosion • Transportation• DepositionTRANSPORTATIONThree modes of moving material– In solution = Dissolved load– Suspended load– Sliding, rolling, bouncing = Bed loadDISSOLVED LOAD• From groundwater, runoff and channel• Supplies ocean with minerals in solutionSUSPENDED LOAD• Most of material transported• Sand, silt, clay• Larger particles in floodBED LOAD• Too large to keep suspended• Grinds channel and downcutsTRANSPORTATION• Competence• CapacityCOMPETENCE• Size of particles• Depends on velocity• Velocity is proportional to the square of competenceCAPACITY• Amount of material• Depends on dischargeCompetence vs. Capacity• Elephant has greater competence• Can carry heavier loadsCompetence vs. Capacity• Many ants is greater capacityThe Work of Streams• Greatest competence with greatest velocity• Greatest capacity with greatest discharge• Maximum during floodsThe Work of Streams•Erosion • Transportation• DepositionBedrock Channel• High gradient• Many rapids and waterfalls• http://www.paul.chesterfield.btinternet.co.uk/pages/landscapes12.htm• Slowing of velocity• Largest particles deposited first•ALLUVIUMDEPOSITIONAlluvial ChannelHigh Velocity in CenterVelocity displaced around meander curveChannel PatternNaturalprogression to more meanderingchannelcharacter• http://www.ucpress.edu/books/pages/6664/6664.ch04.htmlDevelop-ment of meanders• http://www.ucpress.edu/books/pages/6664/6664.ch04.htmlDevelopment of Meanders• http://www.ucpress.edu/books/pages/6664/6664.ch04.htmlChannel developmentChannel developmentChannel developmentFormation of Oxbow Lake• http://www.ucpress.edu/books/pages/6664/6664.ch04.htmlWell Established Meandering Stream• http://www.ucpress.edu/books/pages/6664/6664.ch04.htmlChannel Pattern• High Gradient• Highly variable discharge• High, coarse sediment load• Braided channel developsBraided Channel• http://www.ucpress.edu/books/pages/6664/6664.ch04.htmlGlacial Stream•Dart River• South Island, New Zealand• http://www.bartholmai.com/NZ2/WebPages%20NZ2-Pages/Image51.html• http://www-geology.ucdavis.edu/~gel109/SedStructures/Lg/AKRiverChannel.jpgDeposition by Streams•Delta– Where stream enters standing body of water– Velocity slows, drops its suspended load– Lengthens the stream– Distributaries • http://earth.esa.int/images/article_archive/nile.htmlGlaciers• Rivers of ice• Moving downslope or out from accumulation center• Distinctive erosional and depositional landformsRiver of Ice• http://web.syr.edu/~bwertl/glaciers.htmlAlpine Glacier• http://www.homeralaskacharters.com/glacier_tours.htmU shaped valleyHorns, cirques• http://www.groundtruthtrekking.org/AKMap.phpStriations• http://formontana.net/striations.htmlStriations 200 Ma ago• http://www.seismo.ethz.ch/kradolfer/Angewandte_Erdbebenseismologie/earth/pangaea.htmContinental Ice Sheet• Greenland• http://www.homepage.montana.edu/~geol445/hyperglac/morphology1/Antarctica• http://www.homepage.montana.edu/~geol445/hyperglac/morphology1/Pleistocene Glacial Impact• http://www.soils.wisc.edu/courses/SS325/primary.htmOutlet glacier•
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