1. Streams: Transport to the Ocean
Gary D. McMichael/Photo Researecher

2. The Hydrologic Cycle Describes water’s movement on the surface
P = RO + ET + I
Driven by solar heat
ocean water evaporates
wind carries moist air over land
topography can force moist air to higher altitudes
as air rises, it cools, water condenses to form clouds and then precipitate as rain or snow (P)
rain that falls on the land can:
evaporate back into the atmosphere (E)
be taken up by plants, which return water to the atmosphere
called transpiration (T)
flow over the ground, enter streams and rivers, and ultimately be returned to the sea; called runoff (RO)
infiltrates and becomes groundwater (I)

3. The Hydrologic Cycle

4. This is the “RO” of P = RO + I + ET
STREAMS
This is the “RO” of
P = RO + I + ET

5. Streams Stream : body of water flowing in a channel
The floor of the channel is called the bed.
The sides of the are called the banks.
Flood: when bodies of water overflow their banks and water covers the adjacent land called the floodplain.

6. A stream system network.

7. Drainage basin Area of land surrounded by
topographic divides in which all the
water is directed to a single point
In Hawaii, divides are steep & basins are small!

8. Mississippi River Drainage Basin

9. Drainage Basin of the Colorado River

10. Some terminology VELOCITY (V) - DISTANCE PER UNIT TIME (cm/s, mph)
DISCHAGRE (Q) Total amount of water that passes a given point in a stream per unit time (m3/s) = width (m)  depth (m)  average velocity (m/s)
In the U.S., this is expressed as cubic feet per second (cfs): m3/s = 35.9 ft3/s

11. River at Low Discharge

12. River at High Discharge

13. Downstream changes

14. Longitudinal Stream Profile of the Platt and South Platt Rivers

15. Flooding
Water in the stream is greater than the volume of the channel.
Interval between floods depends on the climate of the region and the size of the channel
In Hawaii, lots of FLASH FLOODS for mountains are steep, flood plains are small & there is lots of CONCRETE!

16. City Built on a Floodplain
Xie Jiahua/China Features/Sygma

17. Recurrence interval
Average time between the occurrences of a given event
The recurrence interval of a flood of a given size at a given place depends on:
• climate of the region
• width of the floodplain
• size of the channel

18. Annual Flood Frequency Curve

19. More stream terms
competence: measure of the largest particles a stream can transport, proportional to v2
capacity: maximum quantity of sediment carried by stream, proportional to Q and v

20. Job of Streams Carry away runoff to lakes and seas
Erode land (degradation)
Transport and deposit sedimentary debris

21. JOB - TO ERODE HYDRAULIC ACTION - flowing water can pick up load
STREAMS CUT, DEEPEN & WIDEN VALLEYS
BY:
HYDRAULIC ACTION - flowing water can pick up load
ABRASION & IMPACT - solid load wears down stream bed
SOLUTION - dissolves channel & load

22. Waterfall Retreating Upriver
Donald Nausbaum

23. Pebbles Caught in Eddies Form Potholes
Carr Clifton/Minden Pictures

24. Stream behavior Mostly determined by velocity and shape of channel.
These factors combine to allow either laminar or turbulent flow.
Turbulent flow is much more erosive & picks load up.
Stream velocities may vary from 0.25 to 7 m/s.

25. Laminar flow
Smooth sheet-like flow at a low velocity
Usually confined to edges and top of stream

26. Laminar flow

27. Turbulent flow Irregular swirling flow
Occurs at most rates of stream flow
Keeps particles in suspension

28. Turbulent flow

29. Laminar to turbulent transition
Laminar flow
Turbulent flow
ONERA

30. JOB - TO TRANSPORT Dissolved load (CATIONS)
Function of stream V & Q
Load is the amount of material carried by a stream in all forms:
Dissolved load (CATIONS)
Suspended load (fine grains)
Bed load (coarse material)

31. Sediment Transport

32. Saltation

33. Grain Size and Flow Velocity

34. Lower Velocities Form Ripples

35. Higher Velocities Form Dunes
ripples
dune
dune

36. Giant ripples in the Channeled Scablands

37. JOB - TO DEPOSIT
As V drops, stream begins to drop its load, coarsest & heaviest first
Forms are streams, deltas, alluvial fans & flood plains

38. Two important stream types
1. Meandering Streams
Gentle gradients, fine-grained alluvium
Minimizes resistance to flow and dissipates energy as uniformly as possible (equilibrium)
Features: point bars, oxbow lake, migrating meanders

39. Meandering River Over Time

40. Meandering River
Point Bar
Peter Kresan

41. Meandering stream, Phnom Penh, Cambodia
Oxbow
Lake

42. Incised Meanders, Utah
Tom Bean

43. Two important stream types
2. Braided Streams
Sediment supply greater than amount stream can support.
At any one moment the active channels may account for only a small proportion of the area of the channel system, but essentially all is used over one season.
Common in glacial, deserts, and mountain regions.

44. Braided River
Tom Bean

45. Brahmaputra River: a braided river
Courtesy NASA

46. Typical Large Marine Delta

47. Alluvial Fans
Michael Collier

48. Parts of a River System

49. Formation of Natural Levees

50. BASE LEVEL
Definition is:
LOWEST LEVEL TO WHICH A STREAM CAN CUT
Think of it as:
Elevation at which a stream enters a large body of water such as a lake or ocean

51. Effects of Building a Dam Original Profile Graded to Regional Base Level

52. Effects of Building a Dam Dam Forms New Local Base Level

53. Effects of Building a Dam Deposition Upstream and Erosion Downstream

54. Formation of River Terraces When Base Level Changes

55. GEOMORPHIC CYCLE STAGES OF LANDSCAPE DEVELOPMENT
HILLS & VALLEYS CUT INTO SIDES OF VOLCANOES
STAGES ARE:
YOUTH
SUBMATURE
MATURE
OLD AGE

56. GEOMORPH I C
CYCLE

57. INITIAL STAGES OF STREAM EROSION IN HAWAII
Runoff is difficult to establish for rock is very porous & slope is steep.
Surface has to be sealed by chemical weathering or ash before it happens.
Happens during Capping Stage
Streams tend to follow lava flow margins or former lava rivers.
It begins at the coast & moves upwards.

58. Development of an experimental drainage network - headward erosion

59. Typical Drainage Networks

60. Amphitheater-Headed Valleys
In Hawai‘i, erosion of the volcanoes by stream erosion and mass wasting produces these distinctive features
Caused by high rainfall, steep radial drainage, and alternating layers strong and weak rocks dipping seaward

62. Stream Piracy or
Stream Capture

63. planezes

64. Ha‘iku Valley

69. Giant “SOIL AVALANCH”

70. Formation of the Nu‘uanu Pali

71. neither erosion nor deposition slope, velocity, and discharge.
Graded stream
Stream in which
neither erosion nor deposition
is occurring, due to an
equilibrium of
slope, velocity, and discharge.

72. THE END