AS Geography Rivers notes

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Rivers
Erosional land forms
Potholes:
Potholes a cylindrical shaped, they vary in depth and can merge together. Some are exposed
above river level
Swirling/eddying water creates a shallow hollow which deepened
Water contains some of the rivers load being carried the river and as this hits the sides of the
holes it abrades it causing it to widen and deepen further, smoothing its edges
This is known as pothole drilling ­ this is most effective during times of high velocity and
discharge
Tend to form above base level where the potential energy is high as potholes are formed
from vertical erosion
Waterfalls:
Found in the upper course of the river
Band of hard rock is arranged horizontally above soft rock
Headwards erosion results in the softer rock being eroded faster than the harder rock,
dominant erosion is abrasion and hydraulic action, and results in creating a steep gradient
This causes undercutting of the soft rock and an overhang develops above the plunge pool
which collapses
The water fall retreats and leaves a steep sided valley ­ a gorge
Plunge pool widens and deepens due to abrasion and attrition the river bed
Example includes High Force Water fall on the River Tees, formed due to resistant dolerite
sitting upon the easily eroded limestone
Rapids:
Occur when a section of the river has a steep gradient which creates turbulent water
Alternating bands of rock, hard rock is more resistant to erosion, soft rocks erode away
causing a change in gradient
Water increases in velocity and this forces the water and rocks to swirl around more.
Meander:
A meander is a sinuous bend in the river
Alternating bars of sediment and water flow creates rifles which direct the flow of a river to
one bank creating undercutting
Erosion is greatest at the outer bank and deposition occurs in the inner bank
Eroded material from the outer back in deposited on the inner bank creates a point bar
When the strongest river flow does not match the shape of the meander e.g. during
flooding, the meander migrates laterally downstream.
Oxbow lake:

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Form when frequent flooding occurs
During flooding the river takes the shortest route and breaks through the narrow gap in the
meander
The sinuous bend in the meander is abandons and the water in it becomes stagnant
Depositional landforms
Deltas:
Located in the lower course of the river
Presence of a large amount of sediment in essential so tends to from large rivers
E.g.…read more

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Unpaired terraces will be present of either side of the river at different levels as the river
erodes laterally
Incised meander:
Two types
entrenched is where the cross profile is symmetrical, form as a result of increased rates of
vertical erosion or the presence of more resistant rock
Ingrown is where the cross profile is asymmetrical, vertical erosion is less rapid so more
lateral erosion takes place…read more

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Hard and soft engineering
Hard engineering: structures are added so that the river channel is directly interfered with so the
speed or flow is altered or the level of storage is changed. There is no concern for the environment.
Dams:
Advantages: effective at regulating flow and controlling flooding
Disadvantages: expensive, time consuming, interferes with river processes e.g. deposition in
calm waters behind dam, and reduction in abrasion.…read more

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