GEOL_0800_Rivers_Fluvial_Processes

GEOL_0800_Rivers_Fluvial_Processes - River Dynamics and...

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River Dynamics and Fluvial Processes
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2 Erosion Processes Dissolution :  Groundwater  flowing through cracks  and in between sediment  grains dissolves or  partially dissolves soluble  minerals. Scouring :  When flowing  water erodes loose soil and  sediment. Abrasion:   Water carrying  sand and gravel acts like  sandpaper. Sandstone polished by abrasion.
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3 Abrasion by waterfalls Waterfalls often create  turbulent eddies that stay  in one spot for a long time. These eddies swirl sand  and gravel around and  around. The result:   Potholes.    Potholes are smooth-sided  bowls or holes bored into  rock by swirling, abrading  sediment.
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4 Abrasion by waterfalls Potholes created by melt waters from the great ice sheets  melting in New York state.
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5 Abrasion by waterfalls
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6 Laminar flow :  All  currents within a flow  are straight, parallel. Turbulent flow :  Under  most natural conditions,  flowing water develops  all sorts of twists and  turns due to: Irregular channel. Friction w/channel. Fluid dynamics. Laminar vs Turbulent Flow Turbulent: Laminar:
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7 Turbulent Flow
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8 Suspended load:   Turbulent flow creates enough vertical  eddies to keep particles above the bottom. Bedload:   Particles that roll or bounce (saltate) along the  bottom. Bedload and Suspended Load
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9 Suspended load tends to be clay and fine silt; fast currents carry  sand in suspension. As a fast current slows, sand and then coarse silt drop to bedload.   Bedload gravel will cease moving (i.e., deposit!). With more slowing, bedload sand, then silt, and finally clay are  deposited. Bedload and Suspended Load
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10 As meanders develop,  the fast currents erode  the cut banks (outside  bends). The helical flow brings  sediment into the  slower currents found  along the inside of the  bends; this creates the  point bars. Meandering river deposits
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11 The channels thus  erode the generally fine  sediments of the flood  plain. These fine sediments  are replaced by the  sand that makes up the  point bars. Produces lenses of  channel sand/gravel in  flood plain muds. Meandering river deposits
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During a flood, the river channel is the deepest part of the  flow and thus has the fastest currents, highest turbulence, and  thus carries a high suspended load of sand, silt, and clay. When the water flows out onto the flood plain, its velocity  immediately drops because shallow flow is much more  affected by friction with the bottom. Flood Plain Deposition
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GEOL_0800_Rivers_Fluvial_Processes - River Dynamics and...

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