Lecture notes for Ch. 9 on Running Water

1. CH. 9 - Running Water

2. Two sources of energy:
1) Internal energy - heat from
core & radioactivity
Powers:
a) EQ’s
b) Volcanoes
c) Mountain building

3. Two sources of energy:
2) Solar energy
Powers:
a) ocean circulation
b) weather & climate
c) hydrologic cycle

4. Hydrologic Cycle
Includes:
- running water
- ground water
- glaciers
- atmosphere (water vapor)

5. Distribution of Earth’s Water
97% ocean water
3% freshwater/brackish water
(Fig. 9.1)

6. Running Water (Streams)
= 0.0001% of hydrosphere
Function of streams is to drain
the land
- 36,000 km3 water drains
annually
- single most important agent
changing landscape

7. Running Water
Source is precipitation (ppt.)
~25% total ppt. becomes surface
water
- depends on infiltration capacity

8. Infiltration capacity depends
on:
1)
2)
3)
4)
5)

9. Drainage Basin
Total land area drained by river
and its tributaries
Tributary = smaller stream
flowing into a larger stream
Ex: Kickapoo Creek into IL River

10. Drainage Basin
Mississippi River = 3,222,000
km2
Amazon River = 5,778,000 km2

11. Drainage Basins
Empty into oceans
Exception: Great Basin in
Nevada
- internal drainage basin (no
streams flow out)

12. Drainage Divide
High point dividing adjacent
drainage basins
Ex: Continental Divide in Rocky
Mtns.

13. Stream Order
First-order = streams with no
tributaries
Second-order = two first-order
streams unite
(only first-order streams as
tributaries)

14. Stream Order
Third-order = two second-order
streams unite
- can have first- and second-
order streams as tributaries

15. Streams
Three main areas:
- zone of erosion
- zone of sediment transport
- zone of deposition

16. Streams
Ability to erode/deposit material
is function of its velocity
Velocity = rate of flow = meters
second

17. Stream Velocity Factors:
1) Gradient – slope of stream
channel
Slope = rise
run
= amount of elevation change
distance measured

18. Gradient
Varies considerably from:
a) one stream to another
b) along the course of any given
stream
Ex: Gradient changes in
Missouri River (maps in lab)

19. Stream Velocity Factors:
2) Channel characteristics
a) Shape – controls amount of
water in contact with channel
Contact with channel causes
velocity to (slow down, speed
up).

20. Channel Characteristics
b) Size – larger channel is more
efficient
Why?

21. Channel Characteristics
c) Roughness –sediment lining
stream channel
Boulders = rough = more
turbulent = slower
Clay/sand = smooth = faster

22. Stream Velocity Factors:
3) Discharge
Amount of water flowing past a
certain point in a given time
period

23. Stream Discharge
Discharge = channel x channel x velocity
width depth
Discharge = meters x meters x meters
second
Discharge = meters3 = cms
second

24. Stream Discharge
Mississippi River
Drainage basin = 3,222,000 km2
Discharge = 17,300 cms
Amazon River
Drainage basin = 5,778,000 km2
Discharge = 212,400 cms

25. Stream Order
As stream order increases:
- discharge __________
- gradient __________
- velocity __________
- channel dimensions ________

26. Stream flow
1) Laminar flow – straight line
- indicates slow velocity or
smooth stream channel

27. Stream flow
2) Turbulent flow
- indicates fast velocity or rough
stream channel (rapids)
- increased erosion
- more sediment in suspension

28. Longitudinal Profile
Cross-sectional view of a river
from headwaters to mouth
Changes:
a) Gradient decreases from head
to mouth
b) Discharge increases towards
mouth of river

29. Base level
Lowest elevation a stream can
erode down its channel
Ultimate base level = sea level
Local base level:
- lakes, resistant rock layers,
larger streams, reservoirs

30. Base Level
Changes in base level causes
changes in stream activities

31. Base Level
Ex 1: Building a dam
- creates new local base level
Changes upstream:
Changes downstream:

32. Base Level
Ex. 2: Draining a lake
- stream channel cuts down to
the next local base level

33. Stream Transport
1) Bed load – material in contact
w/channel bottom
- moves by sliding, rolling,
saltation (jumping motion)
- moves intermittently

34. Stream Transport
2) Suspended Load
- usually fine sand & clay-size
particles
- visible sediment (muddy look of
rivers)
- largest amount of material
carried by streams

35. Stream Transport
3) Dissolved Load
- invisible
- transported regardless of
stream velocity
- precipitates only when stream
chemistry changes

36. Dissolved Load
Measured in parts per million
(ppm)
~4 billion metric tons supplied to
oceans annually

37. Streams’ ability to
erode/deposit depends on:
1) Capacity
- maximum amount of sediment
stream can transport
- directly related to discharge
(volume of water flowing)

38. Streams’ ability to
erode/deposit depends on:
2) Competence – largest
sediment size stream can move
- as velocity doubles,
competence quadruples

39. Flood stages
Greatest power of streams to
erode & transport material
Capacity:
Competence:

40. Types of stream channels
1) Braided
- channel crosses back & forth
- shallow stream channel with
large sediment load

41. Braided streams
Sediment load is deposited
quickly
Caused by:
a) abrupt decrease in gradient
b) decrease in discharge
(drought)

42. Types of stream channels
2) Meandering
- river is confined to one channel
- river channel is curved
Curves = meanders

43. Alluvium
Stream-deposited sediment
- well-sorted by size
As velocity decreases, heaviest
sediment is deposited first

44. Depositional Features
Rapids
Point bars
Floodplains
Natural levee
Back swamp
Yazoo tributary

45. Depositional Features
Delta
Alluvial Fan

46. Erosional Features
Waterfalls
V-shaped valleys
Cutbanks
Meanders
Meander cutoffs
Oxbow lakes

48. Erosional Features
Meander scar
Incised meander - meanders
enclosed in steep valley walls

49. Stages of stream valley
development

50. Stages of Stream Valley
Development
Early stage:
- stream is well above base level
- downcutting is main erosional
work
- narrow V-shaped valley w/no
floodplains

51. Early stage
- relatively straight course
- rapids & waterfalls may be
common

52. Stages of Stream Valley
Development
Middle stage:
- stream closer to base level
- lateral erosion is major
erosional work
- floodplain created & enlarged

53. Middle stage
- meanders
- cutoffs & oxbows may be
present
- floodplain defined by meander
belt

54. Stages of Stream Valley
Development
Late stage:
- stream close to base level
- very wide floodplain
- primary erosional work =
reworking floodplain sediments

55. Late stage
- meanders, cutoffs, oxbows,
meander scars
- natural levee is well developed
- backswamps, yazoo tributaries

56. Rejuvenated Stage
River near base level is uplifted
- downcutting dominates
- incised meanders

57. Ways to Lengthen Valleys:
1) Deposition at mouth of river
Ex: delta
2) Headward Erosion
- erosion cuts into upland area at
the head of the river

58. Stream Piracy
Diversion of one stream channel
by headward erosion of another
stream

59. Stream Piracy
Two streams on opposite sides
of a divide:
Stream w/ steeper gradient cuts
headward faster
- cuts across divide and captures
water from slower stream