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  1. 1. Chapter 16: The FluvialProcessesMcKnight’s Physical Geography:A Landscape Appreciation,Tenth Edition, Hess
  2. 2. The Fluvial Processes• The Impact of Fluvial Processes on theLandscape• Streams and Stream Systems• Stream Channels• Structural Relationships• The Shaping and Reshaping of Valleys• Floodplains• Theories of Landform Development2© 2011 Pearson Education, Inc.
  3. 3. The Impact of Fluvial Processeson the Landscape• Moving water iswidespread• Effective as an agent oferosion and deposition• Influence on landscapedominant• Smoothes irregularities3© 2011 Pearson Education, Inc.Figure 16-1
  4. 4. Streams and Stream Systems• Any channeled flow of water is a stream• Fluvial processes are those which involve runningwater• Unchanneled downslope movement of water—overland flow• Channeled movement of water—streamflow4© 2011 Pearson Education, Inc.
  5. 5. Streams and Stream Systems• Valleys and interfluves– Valley—portion of terrain inwhich a drainage system isestablished– Interfluve—higher landabove valley walls thatseparates adjacent valleys• Drainage basins– Watersheds– Areas that drain to thevalley– Drainage divide5© 2011 Pearson Education, Inc.Figure 16-2
  6. 6. Streams and Stream Systems• Stream orders– Small streams join largerones– Relationship called streamorders– First order versus secondand third order– Smaller numbers in streamorder are more frequent– Larger numbers are longerin length and watershedorder6© 2011 Pearson Education, Inc.Figure 16-4
  7. 7. Streams and Stream Systems• Fluvial erosion and deposition– Splash erosion– Sheet erosion– Rill erosion– Gully erosion• Erosion by streamflow– Once channeled, erosionis greatly enhanced– Erosion increased by debristhe streamflow picks up– Chemical weathering—corrosion7© 2011 Pearson Education, Inc.Figure 16-6
  8. 8. Streams and Stream Systems• Perennial and intermittent streams– Perennial streams—permanent, in humid regions– Intermittent streams—seasonal– Ephemeral streams• The role of floods– Amount of water in a stream, discharge– Most excavating of valleys accomplished duringfloods– Stream gages used to measure flow characteristics– Flood recurrence intervals (i.e., the “100-year flood”)8© 2011 Pearson Education, Inc.
  9. 9. Stream Channels• Streamflow normallyconfined to channels, givingit a three-dimensionalcomplexity• Friction effect of flow alongbottom and sides ofchannel• Highly turbulent flowirregularities produce localcurrents which modifystreamflow9© 2011 Pearson Education, Inc.Figure 16-11
  10. 10. Stream Channels• Stream channel patterns, fourcategories– Straight channels: short andindicative of strong geologicstructure control– Sinuous channels: irregular andgentle curvature that is sinuousin appearance– Meandering channels: highlyvariable curvature– Braided streams: multipleinterwoven channels separatedby loose bars or islands10© 2011 Pearson Education, Inc.Figure 16-14
  11. 11. Structural Relationships• Stream developmentaffected by many factors• Most important factor isgeologic-topographicstructure• Consequent versussubsequent streams• Antecedent streams—thosewhich existed before newuplift occurs• Superimposed streams11© 2011 Pearson Education, Inc.Figure 16-16
  12. 12. Structural Relationships• Stream drainage patterns– Dendritic pattern: treelikepattern with random mergingof streams– Trellis pattern: forms in areasof hard and soft bedrock inclose contact, shape modifiedby structure of bedrock12© 2011 Pearson Education, Inc.Figure 16-19
  13. 13. Structural Relationships• Stream drainage patterns(cont.)– Radial pattern: streamsdescend a concentric uplift– Centripetal pattern: streamsconverge into a uniform basin– Annular pattern: forms inareas of hard and soft domesor basins, flow follows softbedrock and is confined byhard bedrock13© 2011 Pearson Education, Inc.Figure 16-23
  14. 14. The Shaping and Reshapingof Valleys• Valley deepening– Downcutting—hydraulic power ofthe moving water to lower thestreambed– Base level—lower limit to theamount of downcutting that canoccur—ultimate base level is sealevel– Knickpoints—channel irregularitiessuch as rapids and waterfalls– Knickpoint migration14© 2011 Pearson Education, Inc.Figure 16-25
  15. 15. The Shaping and Reshapingof Valleys• Valley widening– Widening slows whenabove the base level– As gradient decreases,stream flow meanders andlateral erosion occurs– Water moves fastest onoutside of curves (cut bank)– Slowest water on inside ofcurves accumulatesalluvium (point bar)15© 2011 Pearson Education, Inc.Figure 16-28
  16. 16. The Shaping and Reshapingof Valleys• Valley lengthening– Headward erosion: fastmoving water from slopebreak between interfluveand valley wall causesmaterial collapse– Results in decrease ofinterfluve area and increasein valley area– Causes a headwardextension of the valley intothe interfluve area16© 2011 Pearson Education, Inc.Figure 16-29
  17. 17. The Shaping and Reshapingof Valleys• Stream capture– Headward erosion causesone stream to be diverted tothe basin of another streamnaturally– Captor versus capturedstream– Beheaded stream– Elbow of capture17© 2011 Pearson Education, Inc.Figure 16-32
  18. 18. The Shaping and Reshapingof Valleys• Delta formation– Slowed flow when itreaches an ocean or lakeresults in depositedsediment– Debris builds up andforms a delta– Distributaries• Deposition in valleys– Aggradation18© 2011 Pearson Education, Inc.Figure 16-34
  19. 19. Floodplains• Low-lying near flat alluvialvalley floor that isperiodically inundated withfloodwaters• Floodplain landforms– Bluffs– Cutoff meander– Oxbow lake– Meander scars– Natural levees– Backswamps– Yazoo streams19© 2011 Pearson Education, Inc.Figure 16-38
  20. 20. Floodplains• Modifying rivers to controlflooding– Humans live on floodplainsdue to flat land, abundantwater, and productive soils– Manmade levees, dams,and overflow floodwayscreated to avert disaster– Example of the MississippiRiver– Human-induced changes tothe deltas and floodplains20© 2011 Pearson Education, Inc.Figure 16-42
  21. 21. Stream Rejuvenation• Lowering of sea level duringice ages or increase ofelevation from tectonic upliftincreases gradients• Gradient increases restart orrejuvenate vertical incisionby streams• Stream terraces• Entrenched meanders21© 2011 Pearson Education, Inc.Figure 16-43
  22. 22. Theories of LandformDevelopment• Davis’s geomorphic cycle– Continuous sequence of uplift,fluvial erosion, and denudation– Youth stage, streams becomeestablished and drainagepattern develops– Mature stage, streams approachequilibrium– Old age stage, erosion reduceslandscape to near base level– Rejuvenation, new uplift restartsthe cycle22© 2011 Pearson Education, Inc.Figure 16-45
  23. 23. Theories of LandformDevelopment• Penck’s Theory of CrustalChange and SlopeDevelopment– Criticisms of Davis’geomorphic cycle– Stated the land slope has aparallel retreat, same slopeangle over time– Many ideas have beensubstantiated bysubsequent works23© 2011 Pearson Education, Inc.Figure 16-46
  24. 24. Theories of LandformDevelopment• Equilibrium theory– Variations in influence of crustal movement and resistanceof underlying rock– Slope forms adjust to geomorphic processes to achieveenergy balance– Shortcomings in areas that are tectonically stable– Prime theory used today24© 2011 Pearson Education, Inc.Figure 16-47
  25. 25. Summary• Fluvial processes are those which involve moving water• Fluvial processes impact the landscape through erosionand deposition• Valleys, interfluves, and drainage basins describe theimpacts of fluvial processes on landscape• Stream orders help describe the structure of streamsystems• Streams affect the landscape through numerous typesof erosion and deposition• Friction along stream channels and turbulence within thechannels affects their patterns25© 2011 Pearson Education, Inc.
  26. 26. Summary• There are four primary types of stream channels• Consequent and subsequent streams develop alongareas of new land formation• Antecedent and superimposed streams result from slowuplift of land affecting the pattern• There are five patterns of stream drainage• Streams affect valleys by both widening them anddeepening them through downcutting• The base level is the lowest level at which a stream willdowncut26© 2011 Pearson Education, Inc.
  27. 27. Summary• Knickpoints are irregularities in the channel flow, such aswaterfalls or rapids• Valleys can be lengthened by headward erosion, streamcapture, and delta formation• Floodplains are flat land areas that have fertile soil butare prone to occasional flooding from nearby streams• Numerous landforms related to floodplains exist• Stream rejuvenation occurs when uplift increases theslope gradient of a stream• There are numerous theories of landform developmentand their relationship to fluvial processes27© 2011 Pearson Education, Inc.