River Processes and Pressures

Question 0

Outline two disadvantages of building levees to control river flooding

Answer 0

• Farmland must be lost to build levees
• Construction of levees could lead to destruction of natural habitat
• Could limit ability of others to use river for fishing and other recreational purposes.

Question 1

Outline two benefits of building levees to control river flooding

Answer 1

Levees have minimal impact on natural river processes

They have a natural looking appearance so are unlikely to affect tourism negatively

Relatively cheap to construct and large areas are protected

Question 2

Examine in the impact of deposition in the formation of landforms in the lower course

Answer 2

On the inside of a bend of a meander deposition takes place which in the slower moving water leading to the formation of a slip-off slope (a gently sloping bank)

A Floodplain is a wide flat area of land on either side of river in the lower course of a river its formed by lateral erosion and Deposition

Deltas are formed when the river deposits its materials faster than the sea can remove it

Levees- Deposition can lead to build up of new land

Question 3

State 2 landforms found in the upper course

Answer 3

V- shaped valley
Waterfalls
Gorges
Interlocking Spurs

Question 4

State 2 landforms found in the middle course

Answer 4

Meanders
Oxbow lakes
Floodplains

Question 5

State 2 landforms found in the lower course

Answer 5

Floodplains

Levees

Question 6

Explain the formation of a V shaped Valley

Answer 6

As the river erodes vertically it leaves behind valley sides that are shaped like a letter V.

The steep valley sides are attacked by weathering such as Freeze- thaw ( when rainfall enters cracks in a rock and then freezes if the temperature is below 0 degrees , the water expands as it turns into rock causing it to break down into smaller pieces).

Question 7

Explain the formation of a V shaped Valley

Answer 7

Vertical erosion in the upper course creates a valley, overtime weathering such as freeze-thaw causes the sides of the valley to collapse, widening the valley

Question 8

Explain the formation of a Interlocking Spurs

Answer 8

The flow of water is weak at the source so the stream stays around the valley side eroding them.the Spurs are left interlocking with those from one side of the valley interlocking with Spurs from the other

Question 9

Explain the formation of a Waterfall (upper course)

Answer 9

As the river passes from hard rock to soft rock the soft rock is eroded vertically at a faster rate. Hydraulic action and abrasion at the base leads to a plunge pool forming.

Eventually the overhanging more resistant rock collapses due to lack of support causing a waterfall to form

Question 10

Explain the formation of a floodplain eg

Arlingham, River Thames

Answer 10

They are formed by lateral erosion which causes the position of meander to change over time. Also high Deposition creates the Floodplain

Erosion occurs on the outside of the meander whilst material is deposited on the inside of the meander

Question 11

Explain the formation of a Meander eg Arlingham, River Severn

Answer 11

Lateral erosion and deposition that takes place in the slower moving water on the inside of the bend. When the river approaches hard rock instead of eroding through it , it erodes around it forming a bend in the river.

Question 12

Explain the formation of a Oxbow lake

Answer 12

As a meander grows and develops the neck of the meander continues to erode and breaks off

Question 13

How is a levee formed?

Answer 13

When a river floods, the largest sediment is deposited first, on the banks. Repeated flooding causes these banks to get higher forming levees which are natural all walls along the banks of river which prevent flooding

Question 14

How does the width of a river channel change from source to mouth?

Answer 14

Increased in width

Question 15

How does the depth of a river channel change from source to mouth?

Answer 15

Gets deeper

Question 16

How does the velocity of a river channel change from source to mouth?

Answer 16

Increases

Question 17

How does the gradient of a river channel change from source to mouth?

Answer 17

Decreases from source to mouth

Question 18

Name the erosion processes

Answer 18

Hydraulic action
Abrasion
Corrosion
Attrition

H.A.C.A

Question 19

Describe what abrasion is

Answer 19

When the river picks up stones causing them to rub against the river bank and wear it away

Question 20

Describe what hydraulic action is

Answer 20

When the force of the water heating the riverbed causes it to where away this happens especially when there is high velocity (nearer the lower course)

Question 21

Describe what corrosion (solution) is

Answer 21

The dissolving of rocks and minerals by river water flowing over them

Question 22

Describe what attrition is

Answer 22

When stones become rounder and smaller overtime from colliding with other particles

Question 23

Name the types of transportation

Answer 23

Suspension
Traction
Saltation

Question 24

What is suspension?

Answer 24

It is when light material is carried across the river

Question 25

What is Traction?

Answer 25

When large boulders and rocks are carried along the river

Question 26

What is saltation?

Answer 26

When small pebbles and stones are bounced along the river bed

Question 27

How does geology influence valley shape and sediment load?

Answer 27

When a river flows over harder rock the valley sides tend to be steep, because erosion is slow, because sediment is slow the sediment load is small

When a river flows over less resistant rock, the valley sides tend to be gentle and sediment load is large because erosion is rapid

Question 28

State 3 types of weathering

Answer 28

Freeze- thaw

Rainfall

Biological weathering

Question 29

What is Freeze- Thaw?

Answer 29

When rainwater enters cracks in rock then freezes if the temperature drops below 0 degrees. The water expands as it turns to ice, this puts pressure on the rock causing it to break into smaller pieces

Question 30

What is the Rainfall (weathering)

Answer 30

When the rain is acidic as it’s been polluted by vehicles and factories, it causes rock to decay

Question 31

Describe what biological weathering

Answer 31

When the roots of plants ( especially trees) can grow into a rock and split the rock apart

Question 32

What are the physical factors that cause flooding?

Answer 32

Intense rainfall- When rain falls too fast to allow full infiltration so it flows across the surface into the river channel.

Snow melt- in places where there’s a lot of snow if temperatures rise above 0 degrees in the spring all the snow that has built up over the months suddenly melts

Impermeable rocks- some rocks like granite do not let water enter the ground so rainwater runs off across the surface into the channel.

Question 33

What are the human factors that cause flooding?

Answer 33

Deforestation -

Question 34

What are the human factors that cause flooding?

Answer 34

Deforestation- if trees are cut down less infiltration will occur (water soaked up from ground) so surface run off will increase causing the river level to rise

Urbanisation -in towns rainwater will find it hard to infiltrate through the hard man made substances such as concrete and Tarmac as they are only partially permeable.

Question 35

Give examples of some hard engineering methods

Answer 35

Levees
Dams eg Three gorges dam, China
The Hoover Dam, California

Question 36

Give an example of a soft engineering methods

Answer 36

Afforestation - trees are planted in drainage basin to increase infiltration and reduce surface run off