Collecting/Transporting Transition Zone
As a stream system transitions
from the collecting zone to the
transporting zon...
Transporting Zone
The transporting zone is dominated by rivers that cross the plains and
demonstrates a balance between ...
Photo by W. W. Little
Rivers
Rivers consist of channels that
carry water and sediment from
the collecting zone to the ...
Types of Rivers
Braided Meandering
There are two primary types of rivers, braided and meandering.
Meandering Rivers
Meandering streams consist of a
single, ribbon-like channel that
weaves back and forth across its
fl...
River Components
The two major subdivisions of a river system are the channel and the
floodplain, which are separated fr...
Modes of Sediment Transport
There are three ways in which sediment is transported by rivers, bedload
(rolling, sliding, ...
Stream Velocity
Because of friction along the banks, flow velocity in a straight channel
is highest near the surface in ...
Stream Velocity Along Bends
Curvature in a channel focuses stream velocity toward the outside of the
bend, increasing ra...
Cut Bank Erosion
Erosion on the cut bank causes the entire channel to migrate toward the
outside of the bend.
Stream Velocity & Meandering
Erosion along the outer bank of a channel bend causes the bend to migrate. This
creates a m...
Helical Flow
Water moving through a river bend develops a corkscrew motion that is
downward along the outer bank, furthe...
Photo by W. W. Little
Photo by W. W. Little
Photo by W. W. Little
Photo by W. W. Little
Point Bar Deposition
Deposition on the inner bank produces gently sloping sand layers that
stack laterally as the channe...
Photo by W. W. Little
Meander Cutoffs
As meander loops grow, they can eventually meet, creating a “shortcut”
as the old loop is cut off from t...
Photo by W. W. Little
Flood Plains
Flood plains are flat areas adjacent to river channels that are covered
with water d...
Photo by W. W. Little
Photo by W. W. Little
Photo by W. W. Little
Braided Rivers
Braided streams consist of
many shallow channels that
bifurcate and rejoin. These
rivers are found wher...
Channel Bifurcation
When a stream contains more sediment than can be carried by its
discharge, it drops the excess and f...
Photo by W. W. Little
Floods
Floods occur when there is more water than the channel can contain.
Floods can be of varying sizes, covering part or all ...
July 1988
July 1993
Photo by W. W. Little
Photographer unknown
Flooding & Urbanization
Because of the amount of concrete and asphalt in urban areas, precipitation that would
normally ...
Photo by W. W. Little
Flood Control
Primary flood control measures include building levees or walls to
contain flow within the river, digging ...
Photo by W. W. Little
Levees
Levees are used to contain flow to within or near the channel.
Photo by W. W. Little
Walls
Walls are constructed to contain flow to within the channel.
Photo by W. W. Little
Bypass Channels
Bypass channels are used to divert flow around flood-prone areas.
Reservoirs
Reservoirs are built to catch and contain water before it reaches the
channel.
Base-level Fluctuation
Stream Terraces
Stream terraces are formed as:
1. A Stream near base level creates a floodplain
2. The land is uplifted...
Dispersal Zone
The dispersal zone occurs where streams empty into lakes and oceans or
onto a valley floor.
Deltas
When a stream enters a body of standing water, such as a lake or the
ocean, velocity decreases and the sediment i...
Delta Formation
Deltas consist of two main
components, distributary
channels that form the main
framework and splays w...
Channel Bifurcation
When a stream enters standing water, its velocity drops to almost zero
and sediment is dropped in th...
Photo by W. W. Little
Photo by W. W. Little
Photo by W. K. Hamblin
Splays
Flooding can breach the channel’s levees, allowing a smaller delta,
called a splay, to develop between the main d...
Delta Evolution
As a stream builds further into the basin, its slope decreases to near zero. The stream
then will typica...
Delta Types
Deltas can have a variety of shapes depending upon the relative
dominance of river, wave, and tidal processe...
Alluvial Fans
Alluvial fans form on flat valley floors at the mouths of deep mountain
canyons as the stream gradient fla...
Bajadas
Bajadas consist of the coalescence of adjacent alluvial fans to form
a blanket.
Fan-Deltas
When a stream empties into a body of water located at the base of a
steep mountain front, it will often produ...
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
Natural Disasters Topic 8 (Drainage Basins & Rivers)
of 75

Natural Disasters Topic 8 (Drainage Basins & Rivers)

Overview of river systems and flooding for a GE-level course in natural disasters.
Published on: Mar 3, 2016
Source: www.slideshare.net


Transcripts - Natural Disasters Topic 8 (Drainage Basins & Rivers)

  • 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.
  • 2. Transporting Zone The transporting zone is dominated by rivers that cross the plains and demonstrates a balance between erosional and depositional processes.
  • 3. Photo by W. W. Little Rivers Rivers consist of channels that carry water and sediment from the collecting zone to the depositional zone.
  • 4. Types of Rivers Braided Meandering There are two primary types of rivers, braided and meandering.
  • 5. 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.
  • 6. 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.
  • 7. 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).
  • 8. 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.
  • 9. 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.
  • 10. Cut Bank Erosion Erosion on the cut bank causes the entire channel to migrate toward the outside of the bend.
  • 11. 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.
  • 12. 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.
  • 13. Photo by W. W. Little
  • 14. Photo by W. W. Little
  • 15. Photo by W. W. Little
  • 16. Photo by W. W. Little
  • 17. 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.
  • 18. Photo by W. W. Little
  • 19. 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.
  • 20. Photo by W. W. Little Flood Plains Flood plains are flat areas adjacent to river channels that are covered with water during floods.
  • 21. Photo by W. W. Little
  • 22. Photo by W. W. Little
  • 23. Photo by W. W. Little
  • 24. 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.
  • 25. 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.
  • 26. Photo by W. W. Little Floods
  • 27. 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.
  • 28. July 1988 July 1993
  • 29. Photo by W. W. Little
  • 30. Photographer unknown
  • 31. 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.
  • 32. Photo by W. W. Little
  • 33. 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.
  • 34. Photo by W. W. Little Levees Levees are used to contain flow to within or near the channel.
  • 35. Photo by W. W. Little Walls Walls are constructed to contain flow to within the channel.
  • 36. Photo by W. W. Little
  • 37. Bypass Channels Bypass channels are used to divert flow around flood-prone areas.
  • 38. Reservoirs Reservoirs are built to catch and contain water before it reaches the channel.
  • 39. Base-level Fluctuation
  • 40. 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.
  • 41. Dispersal Zone The dispersal zone occurs where streams empty into lakes and oceans or onto a valley floor.
  • 42. 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.
  • 43. Delta Formation Deltas consist of two main components, distributary channels that form the main framework and splays which fill the space between distributaries.
  • 44. 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.
  • 45. Photo by W. W. Little
  • 46. Photo by W. W. Little
  • 47. Photo by W. K. Hamblin
  • 48. Splays Flooding can breach the channel’s levees, allowing a smaller delta, called a splay, to develop between the main distributaries.
  • 49. 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.
  • 50. Delta Types Deltas can have a variety of shapes depending upon the relative dominance of river, wave, and tidal processes.
  • 51. 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.
  • 52. Bajadas Bajadas consist of the coalescence of adjacent alluvial fans to form a blanket.
  • 53. 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

Related Documents