Term
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Definition
Sediment is deposited when the energy level (proportional to the stream velocity) of the stream decreases
-> the channel type reflects the energy in the system |
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Term
| Channel morphology is defined by |
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Definition
-the gradient of the channel
-the type of material the channel is incising
-the type and amount of sediment being transported |
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Term
| Depositional Environments and Channel Types |
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Definition
(from high to low energy)
-Braided streams
-meandering streams
-floodplains
-alluvial fans + deltas
-graded (equilibrium) streams and rivers |
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Term
| Fluvial channel patterns: Braided steams |
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Definition
| Streams that flow in broad, shallow channels and consist of multiple sub-channels separated by islands or bards |
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Term
| When do Steams follow a Braided pattern? |
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Definition
-Braided streams develop if the stream is unable to transport all the available bed-load CONTINUOUSLY
-VERY DYNAMIC system
-Braided streams commonly form in regions where the elevation loss is high -> High sediment supply
-Shallow streams, with high velocities
close to the stream bed, therefore..
-Coarse sediments are transported and deposit as bars, locally dividing the channel into two or more channels
(making “braids”) |
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Term
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Definition
-streams that follow a sinuous course are said to meander
-narrow and deep channel
-the degree of meandering is given by the sinuosity (the ratio of channel length to valley length |
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Term
| Erosion and Deposition in Meandering Streams |
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Definition
-Velocity high: bank erosion
-Velocity low: sedimentation and point bar formation
-Evolution of meander can lead to formation of an oxbow lake |
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Term
| When do Streams follow a Meandering Pattern |
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Definition
-Meandering streams commonly form in areas where the elevation loss is low
-low sediment supply
-main transport mechanism: SUSPENDED LOAD
-there is no room left for downward erosion - erosion and energy dissipation in lateral direction |
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Term
| What is the Effect of Gradient on Stream Pattern? |
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Definition
| Cutoff of a meander loop increases the gradient locally and can lead to the development of a braided stream pattern |
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Term
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Definition
| Deposition can occur on floodplains: where streams overflow their channels and inundate adjacent areas, producing floodplain deposits, which are characterized by parallel layers of fine-grained sediment deposited by successive floods |
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Term
| How are alluvial fans formed? |
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Definition
| When streams enter a flat valley floor, causing a loss of energy and sediment deposition |
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Term
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Definition
| When steams enter a body of standing water such as a lake or ocean. Sediment deposition occurs because the stream current slows, dissipates, and loses energy as it moves into and across the body of water |
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Term
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Definition
-Fluvial systems will eventually establish an equilibrium condition with a longitudinal profile that is typically smooth and concave upwards
-in such an equilibrium or graded stream, sediment size being deposited decreases uniformly downstream |
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Term
| When does flooding occur? |
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Definition
When the discharge of the stream becomes too high to be accommodated in the normal stream channel.
When the discharge becomes too high, the stream widens its channel by overtopping its banks and flooding the low-lying areas surrounding the stream |
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