River Systems

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River Systems
2010-05-05 14:36:56
dehon river

Terms and questions on river systems
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  1. What is the most common landform on Earth's surface?
    Stream valleys
  2. A river system consists of a main channel and all of the tributaries that flow into it. IT can be divided into three subsystems. What are the three subsystems?
    a collecting system, transporting system, and dispersing system
  3. A river system is also known as a-
    drainage basin
  4. A river system consists of a main channel and all of the tributaries that flow into it, it is bounded by a _____ (ridge), beyond which water is drained by another system.
  5. A river's _________ consists of the network of tributaries in the headwater region that collect and funnel water and sediment to the main stream.
    Collecting system
  6. Collecting system commonly has what type of drainage pattern?
  7. The _________ system is the main trunk stream, which functions as a channel through which water and sediment flow from the collecting area toward the ocean.
    transporting system
  8. The dispersing system consists of a network of _______ at the mouth of a river, where sediment and water are dispersed into an ocean, lake, or dry basin.
  9. Erosion by ________ is the dominant process in the formation of the landscape.
    running water
  10. How do we know that streams erode the valleys through which they flow? (hint: 5 reasons/relationships)
    • 1. The number of stream segments (tributaries) decreases downstream in a mathematical progression
    • 2. The length of tributaries becomes progressively greater downstream.
    • 3. The gradient, or slope, of tributaries decreases exponentially downstream
    • 4. The stream channels become progressively deeper and wider downstream.
    • 5. The size of the valley is proportional to the size of the stream and increases downstream.
  11. The characteristics of a river change systematically ________.
  12. Rivers are highly complex systems influenced by several variables. As is the case with so many natural systems, if one variable is changed, it produced a change in the others. The most important variables are? (hint: there are 5 of them)
    discharge, velocity, gradient, sediment load, and base level
  13. Define discharge.
    Discharge is the amount of water passing a given point during a specific interval of time.
  14. Flow of water around a meandering being in a river follows a ______ pattern.
  15. The velocity is greatest near?
    the center of the channel and above the deepest part, away from the frictional drag of the channel walls and floor.
  16. Is the velocity of flowing water uniform or not uniform throughout a stream channel?
    not uniform
  17. As the channel curves, the zone of maximum velocity shifts to the _____ of the bend and a zone of minimum velocity forms on the ______ of the curve.
    outside; inside
  18. The velocity of flowing water is proportional to the ______ of the stream channel.
  19. The gradient of a stream channel is what?
    its slope
  20. What are the three ways sediment is transported in a stream channel?
    • 1. Fine particles are moved in suspension (suspended load)
    • 2. Coarse particles are moved by traction (rolling, sliding, and saltation) along the streamed (bed load)
    • 3. Dissolved material is carried in solution (dissolved load)
  21. Define saltation.
    rocks movement in short leaps along the streambed.
  22. What is the base level of a stream?
    the lowest level to which the stream can erode its channel.
  23. The threshold velocity for sediment transport show the _____ at which a stream can pick up and move a particle of a given size.
    minimum velocities
  24. How does a dam effect a stream channel?
    In the reservoir behind a dam, the gradient is reduced to zero. Hence, where the stream enters the reservoir, its sediment load is deposited as a delta and as layers of silt and mud over the reservoir floor. Because most sediment is trapped in the reservoir, the water released downstream has practically no sediment load. The clear water in river downstream of the dam is therefore capable of much more erosion then the previous river, which carried a sediment load adjusted to its gradient
  25. River systems erode the landscape by three main processes. What are those processes?
    removal of regolith, downcutting of the stream channel by abrasion, and headward erosion.
  26. What is regolith?
    rock debris
  27. The tools of erosion are ___ and ____. Transported by a river, they act as powerful abrasives, cutting through the bedrock as they are moved by flowing water.
    sand and gravel.
  28. In the lower parts of the drainage system (transporting and dispersing systems), the gradient of a river is very low. As a result the stream's velocity is reduced, and deposition of much of the sediment load occurs, to create what four things?
    floodplains, alluvial valleys, deltas, and alluvial fans.
  29. The evolution of stream meanders results because erosion occurs on the _____ of a curve in the stream channel, where velocity is _____, and deposition occurs on the _____ of the curve, where velocity is _____.
    outside; high; inside; low
  30. How can a river build its own leeves?
    Natural levees form when a river overflows its banks during flood stage and the water is no longer confined to a channel but flows over the land surface in a board sheet. this unchanneled flow significantly reduces the water's velocity, and some of the suspended sediment settles out. The coarsest material is deposited close to the channel, where it builds up a high embankment.
  31. As a result of natural levees, much of the floodplain may be lower than the river flowing across it. This area is known as the-
  32. A braided stream pattern commonly results if a river is supplied with more sediment than it can carry. T or F
  33. The shape of a delta depends on the balance between what two processes?
    fluvial and marine processes
  34. Where does splays form?
    splays form where a break in a natural levee permits part of the stream to be diverted to the backswamp.
  35. Where do distributaries develop?
    where a stream enters a lake or the sea
  36. What are alluvial fans?
    Alluvial fans are stream deposits that accumulate in dry basins at the base of a mountain front.
  37. Alluvial fans form in _____ regions where a stream enters a dry basin and deposits its load of sediment.
    arid regions