Running WaterErosion and Deposition
Earth ScienceChapter 5
Pages 120-135
Final Exam
• 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
DISCHARGE• Volume of water flowing past a point in a
certain amount of time• Cross sectional area x velocity• Gaging station
Running Water
Discharge Calculation
• http://www.waterwatch.org.au/library/module-4/flow.html#10
Running Water
Willamette Discharge
• http://waterdata.usgs.gov/or/nwis/uv?format=gif&period=31&site_no=14191000
Data 2006 March 9
Willamette Discharge
Data 2006 March 14
• http://waterdata.usgs.gov/or/nwis/uv?format=gif&period=31&site_no=14191000
Longitunal Profile
• Cross section of length of stream• Changes from head to mouth of stream
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
The Work of Streams
TRANSPORTATIONThree modes of moving material
– In solution = Dissolved load– Suspended load– Sliding, rolling, bouncing = Bed load
The Work of Streams
TRANSPORTATIONDissolved load• From groundwater, runoff and channel• Supplies ocean with minerals in
solution
The Work of Streams
TRANSPORTATIONSuspended load• Most of material transported• Sand, silt, clay• Larger particles in flood
The Work of Streams
TRANSPORTATIONBed load• Too large to keep suspended• Grinds channel and downcuts
The Work of Streams
TRANSPORTATION• Competence• Capacity
TRANSPORTATION
COMPETENCE• Size of particles• Depends on velocity• V ~ (competence)2
TRANSPORTATION
CAPACITY• Amount of material• Depends on discharge
Competence vs. Capacity
• Ant has less competence
• Elephant has greater competence
Competence vs. Capacity
• Many ants is greater capacity
The Work of Streams
• Greatest competence with greatest velocity
• Greatest capacity with greatest discharge• Maximum during floods
The Work of Streams
• Erosion • Transportation• Deposition
Stream Valleys
• V shaped• Wide with flat floors
Channel development
Bedrock Channel
• High gradient• Many rapids
and waterfalls
• http://www.paul.chesterfield.btinternet.co.uk/pages/landscapes12.htm
Stream Valleys
• V shaped• Wide with flat floors
Channel Pattern
Naturalprogression to more meanderingchannelcharacter
• http://www.ucpress.edu/books/pages/6664/6664.ch04.html
Broad, flat-bottomed Valley
• Low gradient• Stream cuts into valley walls• Mass wasting delivers sediment to stream
DEPOSITION• Slowing of velocity• Largest particles deposited first• ALLUVIUM
The Work of Streams
High Velocity in Center
Alluvial Channel
Velocity displaced around meander curve
Stream Processes and Floodplain Development
Meandering Stream
Channel development
Develop-ment of
meanders
• http://www.ucpress.edu/books/pages/6664/6664.ch04.html
Development of Meanders
• http://www.ucpress.edu/books/pages/6664/6664.ch04.html
Channel development
Oxbow Lakes
Oxbow Lake Formation
Oxbow Lakes
Meander Scar Formation
Formation of Oxbow Lake
• http://www.ucpress.edu/books/pages/6664/6664.ch04.html
Well Established Meandering Stream
• http://www.ucpress.edu/books/pages/6664/6664.ch04.html
Channel Pattern
• High Gradient• Highly variable discharge• High, coarse sediment load• Braided channel develops
Braided Channel
• http://www.ucpress.edu/books/pages/6664/6664.ch04.html
Glacial 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.jpg
Base Level
• Resistant bed creates a local base level
Base Level
Base Level
• Over time, the resistant bed is eroded• Local base level becomes closer to
ultimate base level
• Eventually resistant rock is eroded to ultimate base level
Base Level
Base Level
• Ultimate profile is idealized graded stream• Gradual decrease in gradient from head to
mouth
Erosion by Streams
• Erode to ‘BASE LEVEL’• Ultimate base level• Local base level (temporary)• Cannot erode below base level
Headward Erosion
http://www.lib.utexas.edu/maps/new_mexico.html
http://www.lib.utexas.edu/maps/national_atlas_1970/ca000043_large.jpg
Headward Erosion
http://www.lib.utexas.edu/maps/colorado.html
Stream Valleys
• V shaped• Wide with flat floors
Broad, flat-bottomed Valley
• Low gradient• Stream cuts into valley walls• Mass wasting delivers sediment to stream
SLOWING OF VELOCITY• Decrease in gradient• Decrease in discharge• Loss of channelization
– Flood stage– Body of water
Deposition
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’
Mississippi Delta
SLOWING OF VELOCITY• Loss of channelization
– Body of water– Flood stage
Deposition
Stream Processes and Floodplain Development
Natural Levee Formation
Natural Levee
Creation
• Competence lost when stream leaves its channel
• Deposits largest particles first
• http://www.ucpress.edu/books/pages/6664/6664.ch04.html
Natural Levees
Natural Levees
Yazoo River
http://www.mvk.usace.army.mil/offices/pp/yazoobackwater/basics.asp?category=basics
Alluvial Fan
http://wiseman.brandonu.ca/earthscience/newpage35.htm
• Badwater Fan, Death Valley, California
Alluvial Fan
http://www.windows.ucar.edu/earth/geology/images/alluvial_fan_lg.jpeg
Drainage Patterns
• Channel layout within a drainage basin• Described by overall shape formed
– Dentritic– Radial– Rectangular– Trellis