Stream Deposition

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Stream Deposition

• Bars
• Braided Streams
• Meandering Streams and Point Bars
• Flood Plains
• Deltas
• Alluvial Fans

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Deposition and Erosion of River Bars
Normal Flow
Flood Increased discharge and erosion!
Post-flood new bars deposited
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Braided Streams
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Gravel Bars
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Braided Stream - Petrified Forest
From http//geoweb.tamu.edu/RGallery/zion2003/six
/6c.html
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Placer Deposits
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Oxbow Lake Development
INCREASING TIME
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Bank erosion - Jan. 1965
Newaukum River, WA
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Bank erosion - Mar. 1965
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Stream Meanders Oxbow Lakes
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Point Bar Development Animation
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Flooding

• Urban Flooding
• Flash Floods
• Controlling Floods
• The Great Flood of 1993

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Location Map Grand Canyon Flood
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Discharge with Time
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River Changes Tanner Rapids
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1997 Flood Floated House
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Effect of Urbanization on Discharge
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Peak Discharge - Cosumnes River, CA
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Levee Break - Cosumnes River
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Flood Frequency Curves
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Flash Floods in Colorado
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Flash Flood Effects
Big Thompson Canyon, CO - 1976
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Flash Flood Effects
Spring Creek - 1997 Fort Collins, CO
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Flood Control Structures
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Great Flood of 1993
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Towns Inundated by 1993 Floodwaters
From http//mo.water.usgs.gov/Reports/1993-Flood/
photos.htm
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1964 Trinity River Flood
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Flood Plains and Bars
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Natural Levees
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Natural Levee Development Animation
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Delta Formation and Morphology

• Deltas form when a stream or river flow into a
  quiet body of water (usually a large lake or
  ocean).
• Surface marked by distributaries
• Small shifting channels that carry water away
  from main river channel
• Sediment deposited at mouth of eventually block
  flow causing shift of deposition
• Internal morphology dominated by
  topset-cross-beds-bottomset sequences
• External morphology depends on environment

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Internal Delta Morphology
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Wave vs. Tidal Deltas
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Stream Dominated Delta
LANDSAT Image of Mississippi River Delta
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Alluvial Fans
Photo credit National Park Service
Badwater Canyon Alluvial Fan Death Valley, CA
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Stream Valley Development

• Downcutting and Base Level
• The Concept of a Graded Stream
• Lateral Erosion
• Headward Erosion and Stream Piracy

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Stream Base Level
Downcutting Process of deepening a stream valley
by erosion of the stream bed. Evolution from
narrow slot to wider V-shaped valley. Base
Level Defined as the limit of downcutting for a
stream. Changes in base level alter the dynamic
equilibrium of the system.
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Ungraded vs. Graded Streams
Graded stream Balance between transport capacity
and sediment load. Maintained by altering the
shape of the channel and stream profile.
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Graded Streams

• Dynamic equilibrium
• Balance between sediment load and transport
  capacity
• Increased stream gradient
• Increases velocity, which allows the stream to
  carry more sediment and larger particles. This
  causes more erosion lowering the gradient.
• Change in sediment load
• Decrease load, can cause erosion, again tending
  to lower the gradient. Common downstream of
  dams. Response of system is NOT always
  predictable!

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Lateral Erosion by Undercutting
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Stream Landforms

• Stream Terraces
• Incised Meanders
• Superposed Streams

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Stream Terraces - Jackson Hole, WY
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Stream Terrace Model
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Goosenecks of the San Juan River, UT
Photo credit Synaptic Gallery
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Incised Meanders
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Superposed Streams
Erosion and downcutting through young horizontal
units
Folded Units
Development of water gap