Rivers Sculpting Earth’s Surface. Rivers of the World Not a large proportion of Earth’s water A...
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RiversSculpting Earth’s Surface
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Rivers of the World
• Not a large proportion of Earth’s water
• A major contributor in sculpting the landscape
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Types of Flow
Laminar Flow– Low velocity– Particles flow in
straight lines– No mixing– Rare in water systems
Turbulent Flow– High velocity– Particles move in
irregular paths– Mixing– Most common type of
flow
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Flows in Rivers
• Velocity
– Fastest in center; slowest at edges
– discharge
– distance per unit of time (ft/s or m/s)
– gradient
• Factors in velocity
– size & roughness
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Gradient
• Gradient (slope)
– vertical drop over distance– highest @ headwater; lowest near base
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Channel Characteristics
•Size
•Roughness
– larger channels have more efficient flow
– Smooth channels promote more uniform flow– Irregular channels
create turbulent flow
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Discharge
• Volume of water flowing past a certain point in a given unit of time (m3/s)
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Erosion, Transportation and Deposition
• Rivers typically display three different behaviors
Erosion – breakdown and removal of material
Transportation – movement of material down a riverDeposition – accumulation along banks and beds of rivers
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Anatomy of a River
• Headwater
• Plains
• Delta
– high slope area– erosion dominant
– transportation dominant
– gradient decreases
–Base level–Deposition dominant
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X-section of a River
• Features– Constantly decreasing
gradient– Overall, smooth and concave upward
curve
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Erosion
•Particles are dislodged from channel and lifted•The stronger the flow, the more particles•More particles, increase erosion (sandpaper)
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Transportation
• Bed load – moves along bottom by skipping or sliding
• Suspended load – fine sediment carried above channel – silt and mud
• Dissolved load – sediment carried in solution - salt
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Transportation• Criteria of a stream’s ability to carry a load
• Competence
• Capacity
–Measures maximum size
– Related to velocity
–Maximum load
– Related to discharge
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Transportation - Landforms
– Complex stream channels separated by sand bars
– Curving stream that migrates side-to-side• Meandering Stream
• Oxbow Lake
• Braided Stream
– A curved lake produced when a stream cuts off a meander
– Coarse material; bedload
– Fine grained; suspended load
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Landform Formation
• Cutbank – banks that are eroded
• Point Bar – areas of deposition
Examples of erosion and deposition:
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Fluvial Landforms Examples
Braided
Meandering
Oxbow
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Deposition
• Base level – limit to where a stream can no longer erode
• When velocity approaches 0 m/s, deposition occurs
− Sea level – ultimate base level
− Lakes and dams local base level
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Drainage Basins• Drainage Basin – The surface area that contains
tributaries and supplies the surface runoff that feeds the river
• Dendritic – irregular branching; uniform underlying material• Radial – diverge from a central area; volcanic domes• Rectangular – right angle bends; contains joints and faults• Trellis – parallel; alternating bedrock
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Floods
•Overflow of a stream channel when discharge exceeds channel capacity
•The most common and destructive geologic hazard
New Orleans, 2005
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Floods
• Causes of Flood– Major storms– Rapid snow melt– Hurricane
Pittsburgh 1996
Sepulveda Basin
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Flood Control
•Artificial Levees • Channelization