Unit 7 Geology

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Unit 7 Geology
2013-03-18 09:32:28
geology rivers streams hydrologic system

Rivers and streams
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  1. On which planets and moon do we see evidence for hydrologic processes?
    • There are large "river channels" that have deeply cut the surface of Mars. Surprisingly, the water that cut these channels did not come from rainfall, but from "groundwater".
    • Recent satellite pictures that were carved by rivers of liquid methane on the Saturn moon of Titan. Thus we know of river channels on two planets and one moon. 
    • River and stream valleys dominate the appearance of the Earth's surface as impact craters dominate the lunar surface.
  2. Define river erosion.
    Surface removal  and transport of rocks and soils by flowing water.
  3. What do the terms gully, arroyo or canyon have in common (what do they represent)?
    River and river channel names reflect local customs of naming.
  4. About what percentage or fraction of the public water supply is derived from rivers?
    Rivers and lakes provide 50%-60%.
  5. What effect do a large number of small lakes have on the ocean (possibly)?
    Some have suggested that the creation of millions of large and small lakes has prevented a rise in sea level. These lakes are preventing the water from returning to the oceans.
  6. Compare headwaters and a mouth of a river.
    Headwaters is the source area for the beginning point of rivers and streams. River mouth final point of water discharge for a river (usually where a delta forms).
  7. Compare a river channel and river banks.
    River channel is wear an elongated depression or passageway containing (or had contained) flowing water River banks is when the ground bordering both sides of a river that serves to confine the water to the natural channel during its normal course of water flow.
  8. Define a tributary within a river system.
    A stream or smaller river that joins a larger river.
  9. Under what conditions can a large river be classified as a tributary further downstream?
    This larger river can be a tributary if it joins an even larger river.
  10. Compare the number of the tributaries upstream verses downstream of a river system?
    The number of tributaries decrease downstream. The river gradient (steepness) generally decreases downstream.
  11. Compare tributary lengths upstream verses downstream in a river system.
    The length increases downstream.
  12. Compare the widths of river channels as you move downstream.
    River channels are wider and deeper downstream.
  13. What is the differences between river water velocity and water discharge velocity?
    • River Discharge velocity is the "calculated"  volume of water of a river as it moves past a specified line per unit of time (i.e. 4,000 cubic feet of water/second).
    • River water velocity (in the US commonly reported as feet/sec) within a river channel.
  14. Interpret a "straight" river channel sketch and describe what part of the river flows the slowest and where it flows the fastest within the channel.
    • Slower water velocity rate is found along the river bottom, along river edges (banks) and along the top of the water (air surface). 
    • The fastest water velocity is found at the center of the river channel, slightly below the surface (on page 3).
  15. Do the same as #14 above , but within a curved river channel.
    • Slower water velocity rates are found on the inside of a curve; here sand will be deposited as sand bars. This also presents a shallow river area that is safer to play and wade. 
    • Faster water velocity rates are found toward the outside of curves; here erosion occurs by undercutting the banks (cut-banks). This is a dangerous area to swim because the water speed could sweep you under the eroding river banks.
  16. Where would we find a safer place to picnic within the area of a river curve?
    At the sand bars.
  17. What name do we give to a wondering or curving bank channel.
    River meanders.
  18. Within a meander, where within the channel would "point bars" and "cut banks" occur?
    • Cut bank are when a river bank eroded on the outside curve of a river channel meander. 
    • Point bars are a crescent-shaped accumulation of sand and gravel deposited on the inside of a river channel.
  19. Describe an oxbow lake and how it is formed? Pick out an oxbow lake in a picture.
    A temporary lake formed in the channel of an abandoned meandering river or stream.
  20. Does the rainfall outside one drainage basin affect another drainage basin? EXAM QUESTION
    Any water (precipitation as rain or snow) that falls within a certain drainage basin is confined  to that river system or drainage.
  21. Describe a continental divide and what happens to the rainfall on one side of this divide.
    The main "divide" (an imaginary line) of any continent that separates rivers that empty into different ocean basins
  22. Describe the dendritic drainage pattern.
    River systems commonly form a dendritic (tree like)  drainage patterns that extend usplope to the eroding edge of the drainage basin.
  23. Besides Earth, where can we find examples of dendritic patterns.
    We have found dendritic drainage patterns on Mars and the moon Titan.
  24. What is a regolith?
    Regolith is loose soil and rock on top of solid rock. It can be washed or can slide into a river channel and can be removed from the area.
  25. What is an incised channel?
    River channel cut into solid rocks (which form canyons).
  26. Describe a river pothole and how it is formed.
    A cone-shaped hole or depression formed in a river bed by swirling and grinding action of individual rocks and gravel.
  27. Describe the direction that a waterfall like Niagara Falls will migrate.
    We can witness the headward (upriver) migration of a waterfall over time, as exemplified by the ever-moving location of Niagara Falls.
  28. Explain the process of river piracy.
    The diversion of the water of one stream into another stream (modifies and changes the drainage basin of more than one river)
  29. Name a Texas river whose channel has been lengthened by river piracy?
    Pecos River
  30. What is a revers sediment load?
    Rocks and soil, etc. carried along by the water movement.
  31. What are dissolved loads?
    Dissolved minerals, acids, ions, gas, and pollutants from areas of heavy vegetation, shale, and igneous ro9cks; in jungles and swamps is represented by dark-colored river waters FYI: usually involves 4 cations and 3 anions.
  32. How might dams create problems for a river delta?
    By upsetting biologic "cycles" and sediment "cycles" that prevent sediment from maintaining and expanding deltas.
  33. Describe and identify from a picture of alluvial fan.
    • Accumulation of sediment in a dry basin. the sediment will form fan-shaped depostis especially in dry, mountainous areas.
  34. Under what conditions do braided streams evolve?
    A stream with a complex of converging and diverging channels (resembles braided hair). More sediment is being deposited in the stream bed than can be removed by the river (deposition along the collecting and transporting subsystems).
  35. What is a floodplain?
    The flat, occasionlally flooded area that borders a river or stream (filled with alluvium).
  36. Describe what is happening to the river sediment load at a delta.
    Most sediment is depostied by floods.
  37. What is the name of classification type for the Mississippi River delta?
    Classified as a "bird-foot delta" because of it's unique shape.
  38. What is river abulsion and how could this affect a city like New Orleans?
    Avulsion represents a shift in the main course of a river to a totally new and ifferent channel that results in forming anew delta in a new location.
  39. Compare a "bank-full" stage to a "flood stage" in regards to a river on a floodplain.
    • Bank full stage is when a river water level that stays abou even with its bank or leeve
    • Flood stage is when the water in the river that overflows its river banks and the water submerges the local area (flooding).
  40. What describes a river "flood"?
    Rivers overflowing their natural levee. Floodsare not a rare event but a seasonal occurrence.
  41. What causes flash floods and why are they so dangerous?
    Cause by a local large downburst of rain. these floods can wash vehicles and people downstream or flood roads and streests and underpasses.
  42. Describe the ownership of streambeds wider thnan 30 feet in TX.
    Any stream bed wider than 30 is publice property, regardless if it has flowing water or is a dry bed. These stream beds are legally navigable streams.
  43. What is the TX law with regards to driving within stream and river beds?
    In January 2004, it became illegal in Texas to drive off road vehicles in river beds.
  44. Name the three largest rivers asociated with the Nueces Drainage Basin.
    • Nueces River
    • Frio River
    • Atascosa River
  45. Name the three river reservoirs that provide water for Corpus Christi.
    • Choke Canyon Lake
    • Lake Corpus Christi
    • Lake Texana
  46. What is the purpose of a salt water barrier dam? ALWAYS ON EXAMS
    To prevent high tides (salt water) from entering the uppr reaches of the river system and contaminating our water supply.