Final Exam Running Water Erosion and Deposition Earth Science Chapter 5 Pages 120-135 Scheduled for 8 AM, March 21, 2006 Bring A scantron form A calculator Your 3 x 5 paper card of formulas Review questions due next time!! (March 16, 2006) will not be accepted late, because key will be posted on website Running Water Discharge Calculation DISCHARGE Volume of water flowing past a point in a certain amount of time Cross sectional area x velocity Gaging station http://www.waterwatch.org.au/library/module-4/flow.html#10 Running Water Willamette Discharge Data 2006 March 9 http://waterdata.usgs.gov/or/nwis/uv?format=gif&period=31&site_no=14191000 1
Willamette Discharge Longitunal Profile Cross section of length of stream Changes from head to mouth of stream Data 2006 March 14 http://waterdata.usgs.gov/or/nwis/uv?format=gif&period=31&site_no=14191000 Longitunal Profile Longitunal Profile Changes from head to mouth of stream Cross section of length of stream Gradient gradually decreases downstream Discharge increases downstream Changes from head to mouth of stream Channel gradient Channel size Discharge Velocity of flow Channel shape Discharge Three modes of moving material In solution = Dissolved load Suspended load Sliding, rolling, bouncing = Bed load 2
Dissolved load From groundwater, runoff and channel Supplies ocean with minerals in solution Suspended load Most of material transported Sand, silt, clay Larger particles in flood Bed load Too large to keep suspended Grinds channel and downcuts Competence Capacity COMPETENCE Size of particles Depends on velocity V ~ (competence) 2 CAPACITY Amount of material Depends on discharge 3
Competence vs. Capacity Competence vs. Capacity Ant has less competence Elephant has greater competence Many ants is greater capacity Greatest competence with greatest velocity Greatest capacity with greatest discharge Maximum during floods Erosion Transportation Deposition Stream Valleys Channel development V shaped Wide with flat floors 4
Bedrock Channel V shaped Wide with flat floors Stream Valleys High gradient Many rapids and waterfalls http://www.paul.chesterfield.btinternet.co.uk/pages/landscapes12.htm Channel Pattern Natural progression to more meandering channel character Broad, flat-bottomed Valley Low gradient Stream cuts into valley walls Mass wasting delivers sediment to stream High Velocity in Center DEPOSITION Slowing of velocity Largest particles deposited first ALLUVIUM 5
Alluvial Channel Velocity displaced around meander curve Channel development Stream Processes and Floodplain Development Meandering Stream Development of meanders Development of Meanders 6
Channel development Oxbow Lakes Oxbow Lake Formation Oxbow Lakes Formation of Oxbow Lake Oxbow Lake Formation Well Established Meandering Stream Channel Pattern High Gradient Highly variable discharge High, coarse sediment load Braided channel develops 7
Braided Channel Glacial Stream Dart River South Island, New Zealand http://www.bartholmai.com/nz2/webpages%20nz2-pages/image51.html Base Level Resistant bed creates a local base level http://www-geology.ucdavis.edu/~gel109/sedstructures/lg/akriverchannel.jpg Base Level Base Level Over time, the resistant bed is eroded Local base level becomes closer to ultimate base level 8
Base Level Base Level Ultimate profile is idealized graded stream Gradual decrease in gradient from head to mouth Eventually resistant rock is eroded to ultimate base level Erosion by Streams Headward Erosion Erode to BASE LEVEL Ultimate base level Local base level (temporary) Cannot erode below base level http://www.lib.utexas.edu/maps/new_mexico.html http://www.lib.utexas.edu/maps/national_atlas_1970/ca000043_large.jpg Headward Erosion Stream Valleys V shaped Wide with flat floors http://www.lib.utexas.edu/maps/colorado.html 9
Broad, flat-bottomed Valley Low gradient Stream cuts into valley walls Mass wasting delivers sediment to stream Deposition SLOWING OF VELOCITY Decrease in gradient Decrease in discharge Loss of channelization Flood stage Body of water Deposition Flows into a body of water Creates delta Delta Formation Deposition decreases gradient Flood stage--gets out of its deposit Delta Formation Flood stage--gets out of its deposit Forms set of DISTRIBUTARIES Delta Formation Forms set of DISTRIBUTARIES 10
Mississippi Delta Deposition SLOWING OF VELOCITY Loss of channelization Body of water Flood stage Stream Processes and Floodplain Development Natural Levee Formation Natural Levee Creation Competence lost when stream leaves its channel Deposits largest particles first Natural Levees Natural Levees 11
Yazoo River Alluvial Fan http://wiseman.brandonu.ca/earthscience/newpage35.htm http://www.mvk.usace.army.mil/offices/pp/yazoobackwater/basics.asp?category=basics Alluvial Fan Drainage Patterns Channel layout within a drainage basin Described by overall shape formed Dentritic Radial Rectangular Trellis Badwater Fan, Death Valley, California http://www.windows.ucar.edu/earth/geology/images/alluvial_fan_lg.jpeg 12
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