Rivers, Floods and Management. (River Landforms)

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What is Fluvial erosion?
This is erosion that is caused by rivers and streams.
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What landforms are caused by Fluvial erosion?
Waterfalls, Potholes and Rapids.
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What is step 1 of a waterfalls generation?
A band of soft rock meets and band of hard rock. This soft rock is eroded faster than the hard rock is, causing a 'step' in the river bed.
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What is step 2 of a waterfalls generation?
The water flowing over this 'step' speeds up due to the lack of friction, this gives it greater erosive power, causing further erosion of the softer rock, that eventually undercuts the harder rock.
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What is step 3 of a waterfalls generation?
As the hard rock is undercut, as a result of the erosion of the softer rock, it can collapse. A deep plunge pool is carved out by abrasion at the foot of he waterfall as the bots of collapsed rock are swirled around by the turbulence.
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what is step 4 of a waterfalls generation?
Over time, more undercutting causes more collapse. The waterfall will retreat (move back up the channel), leaving behind a steep-sided gorge.
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What is a pothole?
This is a small circular hollow in a rivers bed.
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How is a pothole formed?
Turbulence within the river causes the rivers bedload the swirl around in a circular motion (abrasion), causing it to rub and scrape out holes on the river bed.
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What are rapids?
Rapids are relatively steep sections of river where turbulent flow where there are several layers of hard rock. they are a bit like mini-waterfalls.
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What combination forms a Meander?
Erosion and Deposition.
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What is a meander?
A meander is a large, sweeping curve in a rivers middle and lower stages.
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What develops at equally spaced intervals along a stretch of river, that causes the beginning of meanders? and what distances do they alternate at?
These are called Pools (areas of deep water) and Riffles (shallow water) and the distance between pools, or riffles, is roughly 5 - 6 times the width of the rivers bed.
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Where is the flow of a river more efficient? over a pool or riffle?
over a pool, as the water is deeper, it therefore has greater energy and more erosive power.
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why is efficiency lost over riffles?
Because the water is shallow, and friction occurs with the river bed.
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What does the spacing between the riffles and pools cause the rivers flow to do?
It causes the rivers flow to become uneven, and maximum flow is concentrated on one side of the river.
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Why does turbulence increase in and around pools?
This happens because the flow of water speeds up in pools due to the depth of the water, so the flow of the water begins to twist and coil.
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What is the corkscrew-like currents in a rover called?
The Helicoidal flow, which spiral from bank to bank between pools.
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What does the helicoidal flow cause?
This causes more erosion and deepening of the pools. it also causes eroded material to be deposited on the inside of the next bend, where the river loses energy.
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What exaggerates the bends in a river until large meanders are formed?
The combination of deposition and erosion causes this.
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What is an oxbow lake?
This is where a neck of the loop of a meander is broken through, often during flooding.
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Name 4 landforms caused by Fluvial Deposition.
Braiding, Levees, Deltas and Flood plains.
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When does braiding occur?
This occurs when a river is carrying a vast amount of eroded sediment. When the rivers velocity drops, the sediment is deposited in the channel. This causes the river to divide into many small, winding channels.
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What are Levees?
These are natural, raised embankments formed as a river overflows its banks.
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How are Levees formed?
During a flood, material is deposited across the whole flood plain as the river loses velocity and energy due to increased friction. The heaviest material is dropped first, closest to the river channel, this builds up over time creating Levees.
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What are Deltas?
This is a body of sediment that is deposited at the mouth of a river or stream as it enters the sea or ocean.
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How are Deltas formed?
When a river reaches the sea, the energy is absorbed by the slower moving mater of the sea. This causes the river to deposit its loads, this builds up on the sea bed until the sediment rises above sea level. The river then braids, too reach the sea.
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What is a floodplain?
When a river overflows, there is an increase in the wetted perimeter of the river, and reduces the hydraulic radius. This increased friction reduces velocity and causes fine silt and sand to be deposited, across an area called the flood plain.
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What is Rejuvenation of a river?
A river is said to be rejuvenated if its base level is lowered.
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What causes Rejuventation?
It can be caused by either the ground level rising (crust uplift) or by a drop in sea level.
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What is the result of the drop in a rivers base level?
The drop gives the river greater potential energy, increasing its vertical erosion potential. The long profile of the river is extended and a knickpoint will form and mark the junction between the original long profile and the new one.
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What is a Knickpoint?
This is a sharp change in gradient, often a waterfall.
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What distinctive landforms are associated with rejuvenation?
River terraces and incised meanders.
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What is a river terrace?
These are former flood plains which have been left above the level of present day flooding, following vertical erosion.
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What is a incised meander?
These are formed when a river keeps its meandering course as vertical erosion increases. This results in a deep, winding valley with steep sides.
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Card 2

Front

What landforms are caused by Fluvial erosion?

Back

Waterfalls, Potholes and Rapids.

Card 3

Front

What is step 1 of a waterfalls generation?

Back

Preview of the front of card 3

Card 4

Front

What is step 2 of a waterfalls generation?

Back

Preview of the front of card 4

Card 5

Front

What is step 3 of a waterfalls generation?

Back

Preview of the front of card 5
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