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S4: RIVERS

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Kathryn MacDonald

on 20 August 2013

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Transcript of S4: RIVERS

S4: Rivers
THE UPPER COURSE
As we know the upper course channel has little water in it. The channel is shallow enough to wade through and narrow enough to jump across.
What features are found in the upper course?
V-SHAPED VALLEYS
How do they form?
WATERFALLS
A waterfall is a vertical flow of fast flowing water, often from great heights.

Iguazu Falls is located on the border of Argentina and Brazil. It is the greatest set of catarcts in the world
V-shaped Valleys
Waterfalls
Gorges
Potholes
Rapids
Fast Flowing
Vertical Erosion
Why is erosion taking place vertically?
How do they form??
http://www.airpano.ru/files/Brasil-Argentina-Iguazu-Falls-2012/2-2

Waterfalls
The river flows over bands of adjacent hard and soft rock.
The Hydrulic action of the river and the loose rock particles it contains erode away the softer rock.
The differential erosion creates a step in the landscape. The hard rock above is undercut as erosion of the softer rock continues
The overhang of the hard tock can no longer be supported and collapses into the plunge pool channel formed bellow. The position of waterfall moves back upstream.
The broken pieces of rock in the plunge pool get swirled around by the river, abrading the channel further.
The gradient speeds up the river velocity. Erosion continues and the waterfall slowly eats its way upstream (headward ersion) leaving a gorge behind.
How are they formed??
and RAPIDS
http://whs.moodledo.co.uk/mod/resource/view.php?id=51685
GORGES
RAPIDS
How are they formed??
POTHOLES
How are potholes formed??
POTHOLES
How are they formed??
Boulders which have been broken off by errosion, that sit on the river bed, create swirling eddy currents. As the water flows past the boulders it is not yet strong enough to move it by TRACTION. These eddies swirl the boulder round and erode a pothole in the river bed by ABRASION.
A gorge is a deep narrow passage with steep rocky sides. They are formed as a waterfall retreats back upstream.
http://www.airpano.com/360Degree-VirtualTour.php?3D=Grand_Canyon_USA
THE MIDDLE COURSE
What features are found in the middle course??
Meanders
Wider Channel
River beaches and cliffs
Lateral Erosion
The Middle course has much more water in it due to all the tributaries which join the main channel.
MEANDERING CHANNELS
Panoramic views of meanders in Utah
http://www.airpano.com/360Degree-VirtualTour.php?3D=Goosenecks-Utah-USA
MEANDERS
How are they formed??
BBC CLASS CLIP 403
The deeper the channel the faster the flow.
The faster it flows the deeper it erodes.

The shallower the channel the slower the flow.
The slower it flows the more deposition takes place.
AND
KEY POINTS...
Meanders
How are they formed??
Inside of the bend
Outside of the bend
The river is slower and material is deposited, creating a beach. Rifles are also found here. There is more friction on the inner bend.
Bends are created by the force of the water (hydraulic action) and by the river load wearing away the banks (abrasion).
Force of the water erodes and undercuts the river bank. The water flow has more energy due to decreased friction and pools. This forms a steep river cliff.
MEANDERS
The Middle Course
The Upper Course
The Lower Course
How do they form??
More on...
RIVER BEACHES & CLIFFS
River Cliff = EROSION
River Beach = DEPOSITION
Which direction is the river now eroding? WHY?
When the river cliff colapses the sediment becomes bedload in the channel. The river transports these deposits downstream until they are deposited to form river beaches or point bar.
The river is using almost all its energy to move downstream due to the friction created by the large and angular bedload found in the channel. Boulders are too heavy to be transported downstream.

In which direction do you think the valley is eroding??
V-SHAPED VALLEYS:
How do they form?
-
The end result is a steep sided valley that has a shape of a letter V.

- As the river cuts down, the steep sides are attacked by weathering. This breaks up and loosens the soil and rock.

- The river erodes downwards as bouldersm stones and rock particles are bounced and scraped along the channel bed.

- The loosened material slowly creeps down the slope because of gravity or is washed into the river by rainwater. The river carries it away.
Copy out the diagrams. Write the processes in the order they happen.
THE LOWER COURSE
What features can be found in the lower course??
Wide flat floodplain
Deposition
Ox-bow lakes
Deltas
Embankments
By the lower course the beds and banks have been smoothed by hydraulic action. Friction is at its lowest so the river flows fast.
OX-BOW LAKES
How do they form??
Task: In pairs, discuss how you think Ox-Bow lakes are formed.
Ox-Bow lake
Meander
OX-BOW LAKES
How do they form?
OX-BOW LAKES
How do they form?
Learning Intention: To deepen our knowledge of the features found in the upper course of a river.
Success criteria- Complete Worksheet 3c/G
Full transcript