Easc116 rivers


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Lecture notes for Ch. 9 on Running Water

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Easc116 rivers

  1. 1. CH. 9 - Running Water
  2. 2. Two sources of energy:1) Internal energy - heat from core & radioactivityPowers:a) EQ’sb) Volcanoesc) Mountain building
  3. 3. Two sources of energy:2) Solar energyPowers:a) ocean circulationb) weather & climatec) hydrologic cycle
  4. 4. Hydrologic CycleIncludes:- running water- ground water- glaciers- atmosphere (water vapor)
  5. 5. Distribution of Earth’s Water97% ocean water3% freshwater/brackish water(Fig. 9.1)
  6. 6. Running Water (Streams)= 0.0001% of hydrosphereFunction of streams is to drain the land- 36,000 km3 water drains annually- single most important agent changing landscape
  7. 7. Running WaterSource is precipitation (ppt.)~25% total ppt. becomes surface water- depends on infiltration capacity
  8. 8. Infiltration capacity dependson:1)2)3)4)5)
  9. 9. Drainage BasinTotal land area drained by river and its tributariesTributary = smaller stream flowing into a larger streamEx: Kickapoo Creek into IL River
  10. 10. Drainage BasinMississippi River = 3,222,000 km2Amazon River = 5,778,000 km2
  11. 11. Drainage BasinsEmpty into oceansException: Great Basin in Nevada- internal drainage basin (no streams flow out)
  12. 12. Drainage DivideHigh point dividing adjacent drainage basinsEx: Continental Divide in Rocky Mtns.
  13. 13. Stream OrderFirst-order = streams with no tributariesSecond-order = two first-order streams unite(only first-order streams as tributaries)
  14. 14. Stream OrderThird-order = two second-order streams unite- can have first- and second- order streams as tributaries
  15. 15. StreamsThree main areas:- zone of erosion- zone of sediment transport- zone of deposition
  16. 16. StreamsAbility to erode/deposit material is function of its velocityVelocity = rate of flow = meters second
  17. 17. Stream Velocity Factors:1) Gradient – slope of stream channelSlope = rise run = amount of elevation change distance measured
  18. 18. GradientVaries considerably from:a) one stream to anotherb) along the course of any given streamEx: Gradient changes in Missouri River (maps in lab)
  19. 19. Stream Velocity Factors:2) Channel characteristicsa) Shape – controls amount of water in contact with channelContact with channel causes velocity to (slow down, speed up).
  20. 20. Channel Characteristicsb) Size – larger channel is more efficientWhy?
  21. 21. Channel Characteristicsc) Roughness –sediment lining stream channelBoulders = rough = more turbulent = slowerClay/sand = smooth = faster
  22. 22. Stream Velocity Factors:3) DischargeAmount of water flowing past a certain point in a given time period
  23. 23. Stream DischargeDischarge = channel x channel x velocity width depthDischarge = meters x meters x meters secondDischarge = meters3 = cms second
  24. 24. Stream DischargeMississippi RiverDrainage basin = 3,222,000 km2Discharge = 17,300 cmsAmazon RiverDrainage basin = 5,778,000 km2Discharge = 212,400 cms
  25. 25. Stream OrderAs stream order increases:- discharge __________- gradient __________- velocity __________- channel dimensions ________
  26. 26. Stream flow1) Laminar flow – straight line- indicates slow velocity or smooth stream channel
  27. 27. Stream flow2) Turbulent flow- indicates fast velocity or rough stream channel (rapids)- increased erosion- more sediment in suspension
  28. 28. Longitudinal ProfileCross-sectional view of a river from headwaters to mouthChanges:a) Gradient decreases from head to mouthb) Discharge increases towards mouth of river
  29. 29. Base levelLowest elevation a stream can erode down its channelUltimate base level = sea levelLocal base level:- lakes, resistant rock layers, larger streams, reservoirs
  30. 30. Base LevelChanges in base level causes changes in stream activities
  31. 31. Base LevelEx 1: Building a dam- creates new local base levelChanges upstream:Changes downstream:
  32. 32. Base LevelEx. 2: Draining a lake- stream channel cuts down to the next local base level
  33. 33. Stream Transport1) Bed load – material in contact w/channel bottom- moves by sliding, rolling, saltation (jumping motion)- moves intermittently
  34. 34. Stream Transport2) Suspended Load- usually fine sand & clay-size particles- visible sediment (muddy look of rivers)- largest amount of material carried by streams
  35. 35. Stream Transport3) Dissolved Load- invisible- transported regardless of stream velocity- precipitates only when stream chemistry changes
  36. 36. Dissolved LoadMeasured in parts per million (ppm)~4 billion metric tons supplied to oceans annually
  37. 37. Streams’ ability toerode/deposit depends on:1) Capacity- maximum amount of sediment stream can transport- directly related to discharge (volume of water flowing)
  38. 38. Streams’ ability toerode/deposit depends on:2) Competence – largest sediment size stream can move- as velocity doubles, competence quadruples
  39. 39. Flood stagesGreatest power of streams to erode & transport materialCapacity:Competence:
  40. 40. Types of stream channels1) Braided- channel crosses back & forth- shallow stream channel with large sediment load
  41. 41. Braided streamsSediment load is deposited quicklyCaused by:a) abrupt decrease in gradientb) decrease in discharge (drought)
  42. 42. Types of stream channels2) Meandering- river is confined to one channel- river channel is curvedCurves = meanders
  43. 43. AlluviumStream-deposited sediment - well-sorted by sizeAs velocity decreases, heaviest sediment is deposited first
  44. 44. Depositional FeaturesRapidsPoint barsFloodplainsNatural leveeBack swampYazoo tributary
  45. 45. Depositional FeaturesDeltaAlluvial Fan
  46. 46. Erosional FeaturesWaterfallsV-shaped valleysCutbanksMeandersMeander cutoffsOxbow lakes
  47. 47. Erosional FeaturesMeander scarIncised meander - meanders enclosed in steep valley walls
  48. 48. Stages of stream valleydevelopment
  49. 49. Stages of Stream ValleyDevelopmentEarly stage:- stream is well above base level- downcutting is main erosional work- narrow V-shaped valley w/no floodplains
  50. 50. Early stage- relatively straight course- rapids & waterfalls may be common
  51. 51. Stages of Stream ValleyDevelopmentMiddle stage:- stream closer to base level- lateral erosion is major erosional work- floodplain created & enlarged
  52. 52. Middle stage- meanders- cutoffs & oxbows may be present- floodplain defined by meander belt
  53. 53. Stages of Stream ValleyDevelopmentLate stage:- stream close to base level- very wide floodplain- primary erosional work = reworking floodplain sediments
  54. 54. Late stage- meanders, cutoffs, oxbows, meander scars- natural levee is well developed- backswamps, yazoo tributaries
  55. 55. Rejuvenated StageRiver near base level is uplifted- downcutting dominates- incised meanders
  56. 56. Ways to Lengthen Valleys:1) Deposition at mouth of river Ex: delta2) Headward Erosion- erosion cuts into upland area at the head of the river
  57. 57. Stream PiracyDiversion of one stream channel by headward erosion of another stream
  58. 58. Stream PiracyTwo streams on opposite sides of a divide:Stream w/ steeper gradient cuts headward faster- cuts across divide and captures water from slower stream