The document summarizes key aspects of river systems and their transport of sediment. It describes how rivers transition from steep mountain headwaters to flatter plains, carrying sediment in various modes of transport. It also discusses characteristics of meandering and braided rivers, and how river channels migrate and deposit sediment in point bars and during floods. The document concludes by outlining features that form as rivers enter standing bodies of water, such as deltas, alluvial fans, and fan-deltas.

1. Collecting/Transporting Transition Zone
As a stream system transitions
from the collecting zone to the
transporting zone, channels
become wider and flatter with
fewer tributaries.

6. Transporting Zone
The transporting zone is dominated by rivers that cross the plains and
demonstrates a balance between erosional and depositional processes.

7. Photo by W. W. Little
Rivers
Rivers consist of channels that
carry water and sediment from
the collecting zone to the
depositional zone.

8. Types of Rivers
Braided Meandering
There are two primary types of rivers, braided and meandering.

9. Meandering Rivers
Meandering streams consist of a
single, ribbon-like channel that
weaves back and forth across its
floodplain. These rivers are
found where there is adequate
discharge to carry all the
available sediment, such as across
broad plains.

10. River Components
The two major subdivisions of a river system are the channel and the
floodplain, which are separated from each other by levees. Oxbow lakes
and yazoo streams are also common features.

11. Modes of Sediment Transport
There are three ways in which sediment is transported by rivers, bedload
(rolling, sliding, saltation), suspended load (floating), and dissolved load
(individual ions).

12. Stream Velocity
Because of friction along the banks, flow velocity in a straight channel
is highest near the surface in the middle of the stream.

13. Stream Velocity Along Bends
Curvature in a channel focuses stream velocity toward the outside of the
bend, increasing rates of erosion along the outer bank and producing an
asymmetrical channel profile.

14. Cut Bank Erosion
Erosion on the cut bank causes the entire channel to migrate toward the
outside of the bend.

15. Stream Velocity & Meandering
Erosion along the outer bank of a channel bend causes the bend to migrate. This
creates a meandering pattern, as the line of maximum flow velocity crosses back and
forth across the channel from one bend to the next.

16. Helical Flow
Water moving through a river bend develops a corkscrew motion that is
downward along the outer bank, further increasing erosion, and upward
along the inner bank, resulting in deposition.

17. Photo by W. W. Little

18. Photo by W. W. Little

19. Photo by W. W. Little

20. Photo by W. W. Little

21. Point Bar Deposition
Deposition on the inner bank produces gently sloping sand layers that
stack laterally as the channel migrates with outer bank erosion. These
form bodies called point bars.

22. Photo by W. W. Little

23. Meander Cutoffs
As meander loops grow, they can eventually meet, creating a “shortcut”
as the old loop is cut off from the main channel. The result is an oxbow
lake.

27. Photo by W. W. Little
Flood Plains
Flood plains are flat areas adjacent to river channels that are covered
with water during floods.

28. Photo by W. W. Little

29. Photo by W. W. Little

30. Photo by W. W. Little

31. Braided Rivers
Braided streams consist of
many shallow channels that
bifurcate and rejoin. These
rivers are found where there
is more sediment available
than can be carried by the
available discharge, such as
mountain foothills.

32. Channel Bifurcation
When a stream contains more sediment than can be carried by its
discharge, it drops the excess and flows around it, forming interchannel
bars.

35. Photo by W. W. Little
Floods

36. Floods occur when there is more water than the channel can contain.
Floods can be of varying sizes, covering part or all of the flood plain.

37. July 1988
July 1993

40. Photo by W. W. Little

45. Photographer unknown

46. Flooding & Urbanization
Because of the amount of concrete and asphalt in urban areas, precipitation that would
normally infiltrate through the surface and move to the water table is, instead, funneled
to river channels, increasing the frequency and severity of flooding unless prevented by
artificial measures.

47. Photo by W. W. Little

49. Flood Control
Primary flood control measures include building levees or walls to
contain flow within the river, digging bypass channels to divert water
around flood-prone areas, and constructing dams to create reservoirs
for temporary water storage.

50. Photo by W. W. Little
Levees
Levees are used to contain flow to within or near the channel.

51. Photo by W. W. Little
Walls
Walls are constructed to contain flow to within the channel.

52. Photo by W. W. Little

53. Bypass Channels
Bypass channels are used to divert flow around flood-prone areas.

54. Reservoirs
Reservoirs are built to catch and contain water before it reaches the
channel.

55. Base-level Fluctuation

57. Stream Terraces
Stream terraces are formed as:
1. A Stream near base level creates a floodplain
2. The land is uplifted or base-level falls
3. The stream cuts to the lower base-level and carves a new floodplain.

59. Dispersal Zone
The dispersal zone occurs where streams empty into lakes and oceans or
onto a valley floor.

60. Deltas
When a stream enters a body of standing water, such as a lake or the
ocean, velocity decreases and the sediment it has been transporting is
dropped to form a delta.

61. Delta Formation
Deltas consist of two main
components, distributary
channels that form the main
framework and splays which
fill the space between
distributaries.

62. Channel Bifurcation
When a stream enters standing water, its velocity drops to almost zero
and sediment is dropped in the middle of the channel forming a bar.
The stream then bifurcates into smaller channels that move around the
mid channel bar.

63. Photo by W. W. Little

64. Photo by W. W. Little

65. Photo by W. K. Hamblin

66. Splays
Flooding can breach the channel’s levees, allowing a smaller delta,
called a splay, to develop between the main distributaries.

68. Delta Evolution
As a stream builds further into the basin, its slope decreases to near zero. The stream
then will typically break through its margin at some point upstream and find a
steeper path to the basin. The abandoned lobe then subsides and is reworked by
marine processes.

69. Delta Types
Deltas can have a variety of shapes depending upon the relative
dominance of river, wave, and tidal processes.

72. Alluvial Fans
Alluvial fans form on flat valley floors at the mouths of deep mountain
canyons as the stream gradient flattens and flow becomes unconfined.

74. Bajadas
Bajadas consist of the coalescence of adjacent alluvial fans to form
a blanket.

75. Fan-Deltas
When a stream empties into a body of water located at the base of a
steep mountain front, it will often produce a feature that has
characteristics of both deltas and alluvial fans.
Photo by W. W. Little