Chapter 9 (exam three)
29 Cards in this Set
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The hydrologic cycle
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a summary of the circulation of Earth’s water supply
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processes involved in hydrologic cycle
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Precipitation: condensed water molecules that fall from the atmosphere to earth
Evaporation: the transfer of liquid water at the surface to water vapor in the atmosphere
Infiltration: the movement of surface water into the ground through the soil or rock fractures
Runoff: water t…
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Sheet flow
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thin broad sheets of water flowing across the ground
Sheet flow develops into tiny channels called rills, which eventually form larger channels
depends on infiltration capacity
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Infiltration capacity
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how much water can seep into the ground
Infiltration capacity is controlled by:
Intensity and duration of rainfall
How wet or dry the soil was before the rain
Soil texture
Slope of the land
Nature of the vegetative cover
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Drainage basin
Divide
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the land area that contributes water to a stream
Drainage basin of one stream is separated from the drainage basin of another by an imaginary line called a divide (ridges to continental divides)
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Laminar streamflow
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slow moving water moves in a relatively straight line
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Turbulent streamflow
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faster moving water is much more erratic, and may have whirlpools, eddies, and rapids
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Changes from upstream to downstream
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Discharge increases as a result of more tributary streams that drain into the main stream
Channel size increases to accommodate more water from the tributary streams
Gradient decreases to a more gentle slope
Channel roughness decreases with a gentler slope
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Base levels
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the lowest point to which a stream can erode
two types:
Ultimate (sea level)
Local or temporary (lakes, resistant rock layers, larger main streams)
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dissolved stream load
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material that is in solution from the chemical erosion of soluble rocks (limestone, marble, rock salt, rock gypsum)
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suspended stream load
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usually silt and clay sized particles that are carried with the current
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bed stream load
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coarser particles (sand sized and up) that moves along the bottom of the channel
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alluvium deposition spots
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Examples include point bars, braided streams, sand and gravel bars, deltas
Bars
May be in the middle of the channel
May be on the inside of a stream meander
Braided streams – many channels that interlace, very commonly associated with glaciers and deltas
Deltas – fan shaped are…
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natural levees
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form parallel to the stream channel by successive floods over many years
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back swamps
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marshy land between the levees and the valley walls
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Yazoo tributaries
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small streams that run parallel to the main river, situated between the levee and the valley wall
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V shaped stream valley
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The gradient is steeper at the headwaters, which causes valley deepening
Downward erosion dominates, and develops features such as rapids and waterfalls
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broad flood plain stream valley
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Towards the mouth of the river, the gradient is more gentle, allowing for valley widening
The stream begins to meander side to side
This widens the valley and develops features such as floodplains, oxbows, yazoos, etc
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cut bank
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feature of stream valley
outside of a meander
erosion is active
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point bar
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feature of stream valley
inside of a meander
deposition is active
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cutoffs
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feature of stream valley
As the stream meanders, part of a meander may become cut off from the rest of the river
these segments can form oxbow lakes
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incised meandors
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feature of stream valley
Meanders are carved in steep, narrow valleys
Caused by a drop in base level or uplift of the region by tectonic forces
Common in the Colorado Plateau
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terraces
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feature of stream valley
Remnants of a former floodplain
River has adjusted to a relative drop in base level by downcutting
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drainage patterns
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Dendritic – irregularly branching tributaries
Most common type of drainage pattern
Radial – streams diverge from a center point
Typical of streams that flow off volcanoes
Rectangular – streams bend at right angles
Caused by fractures in the bedrock that are perpendicular to eac…
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floods
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Any event in which the amount of water in a stream becomes too large for the channel to hold
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regional floods
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Caused by long-duration precipitation (or snow melt)
Flood waters cover a large geographic area
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flash floods
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Caused by intense, relatively short-duration precipitation
more localized areas
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ice-jam floods
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Ice flowing along partially frozen rivers may block part or all of the channel
The ice creates a dam, causing water to flood over its banks
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dam failure
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Man-made and natural dams may fail under any number of circumstances
Too much water from previous floods, earthquakes, etc.
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Chapter 10