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Landforms Made by Running Water
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Landforms Made by Running Water

• Fluvial Processes and Landforms
• Slope Erosion
• The Work of Streams
• Stream Gradation
• Fluvial Processes in an Arid Climate

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Fluvial Processes and Landforms

• fluvial landforms are shaped by the fluvial
  processes of overland flow and stream flow.
  Wherever rain falls, these processes act to
  create erosional and depositional landforms

Figure 16.1, p. 547
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Slope Erosion

• soil erosion occurs when overland flow moves soil
  particles down-slope
• erosion is greatest on bare slopes of fine
  particles, carving rills and gullies
• a vegetation cover greatly reduces soil erosion

Figure 16.3, p. 548
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Slope Erosion

• soil particles moved down-slope eventually reach
  the base of the slope, where they come to rest
  and accumulate in a thickening layer termed
  colluvium
• if not deposited as colluvium, sediment carried
  by overland
• flow eventually reaches a stream, is carried
  farther
• down-valley and may accumulate as alluvium (a
  stream-laid sediment deposit).

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The Work of Streams

• streams erode their beds and banks by hydraulic
  action, abrasion, and corrosion
• abrasion by stones on a bedrock riverbed can
  create deep depressions known as potholes

Figure 16.6, p. 551
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The Work of Streams

• streams carry dissolved matter, sediment in
  suspension, and a bed load of larger particles
  bumped and rolled along the bottom
• a streams capacity to carry sediment increases
  sharply with its velocity

Figure 16.7, p. 551
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Stream Gradation

• over time, a stream develops a graded profile in
  which the gradient
• is just sufficient to carry the average annual
  load of water and sediment
• produced by its drainage basin

Figure 16.9, p. 553
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Niagara Falls
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Stream Gradation

• Evolution of a graded stream
• (a) stream established on a land surface
  dominated by landforms of recent tectonic
  activity
• (b) gradation in progress - the lakes and marshes
  drained, the gorge is deepening, and the
  tributary valleys are extending
• (c) graded profile attained floodplain
  development is beginning, and the widening of the
  valley is in progress
• (d) Floodplain widened to accommodate meanders

(b)
(a)
(c)
(d)
Figure 16.10, p. 554
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Stream Gradation

• evolution of side slopes following stream
  gradation, the valley walls become gentler in
  slope, and the bedrock is covered by soil and
  weathered rock

Figure 16.13, p. 556
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Stream Gradation

• alluvial terraces form when an
• aggrading river loses its
• sediment input and begins
• degrading its bed, leaving terraces behind as it
  cuts deeper into its sediment-filled valley
• an alluvial river, with its low
• gradient and broad floodplain, creates
  characteristic landforms including bluffs,
  meanders, cutoffs, ox-bow lakes, and natural
  levees

Figure 16.19, p. 559
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Stream Gradation

• as a flood plain develops it widens over time
  creating a flat valley floor where the river
  meanders back and forth (ALLUVIAL MEANDERS)
• (on the inside of each bend point bar
  deposition, on the outside of each bend erosion)

Figure 16.12, p. 555
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Stream Gradation

• accelerated soil erosion and glacial activity can
  increase the amount of sediment brought to a
  river system, causing aggradation and the
• development of braided streams and river segments

Figure 16.18, p. 559
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Stream Gradation

• floodplain landforms of an alluvial river as
  meanders wander downriver, they create a variety
  of landforms, including ox-bow lakes, cutoffs,
  and natural levees

Figure 16.21, p. 563
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Stream Gradation

• where rapid uplift causes meandering rivers to
  cut deeply into bedrock, entrenched meanders are
  formed

Figure 16.22, p. 563
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Stream Gradation

• the geographic cycle traces the fate
• of rivers and fluvial landforms from
• an initial uplift creating steep slopes
• and canyons to a final low, gently
• rolling surface called a peneplain
• the equilibrium approach sees
• fluvial landforms as reflecting a
• balance between processes of uplift
• and denudation acting on rocks of
• varying resistance to erosion
• uplift and rejuvenation

Figure 16.19, p. 559
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Fluvial Processes in an Arid Climate

• stream water flow to ground water In humid
  regions - a stream channel receives ground water
  through seepage
• in arid regions - stream water seeps out of the
  channel and into the water table below

Figure 16.28, p. 567
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Fluvial Processes in an Arid Climate

• although rain is infrequent in desert
  environments, running water shapes desert
  landforms with great effectiveness because of the
  lack of vegetation cover

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Fluvial Processes in an Arid Climate

• alluvial fans are common features of arid
  landscapes
• they occur where streams discharge water and
  sediment from a narrow canyon or gorge onto an
  adjacent plain

Figure 16.29, p. 568
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Fluvial Processes in an Arid Climate

• landforms of mountainous deserts include alluvial
  fans, dry lakes or playas, and pedimentsrock
  platforms veneered with alluvium

Figure 16.31, p. 569
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Yangtze River, China
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Yangtze River Dam, China