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