Topic 4, EQ4

Question 1

What is meant by the long profile of a river?

Answer 1

A diagram which shows the altitude of a river from the source to the mouth. It is usually a concave shape which slowly adopts a gentler slope towards the mouth of the river.

Question 2

How does the River Eden’s landscape change along its profile?

Answer 2

Upper Course: Here there is a very high altitude, about 600 metres above sea level, and the channel consists of mostly hard and resistant rock. The channel is steep-sided due to vertical erosion and the channel has a steep gradient. Lastly, the narrow channel means the discharge and velocity is low, this is due to friction from the rough channel sides and beds.
Middle Course: The river channel consists of less resistant and soft sandstone, this is easily eroded. There is now enough power in the river for lateral erosion, leading to a wider rover valley, and discharge increases. Here the gradient is much gentler.
Lower Course: The valley is very wide and flat. Here the gradient is minimal and the velocity has increased due to a smooth channel bed and sides. Lastly, there is a very large discharge.

Question 3

What are the reasons for these changes?

Answer 3

As the river channel connects with more tributaries the discharge will increase, so will the velocity. This velocity will also lead to further erosion, both vertical and lateral, and the will create a wide and deep river channel. The further erosion will also erode sediment in the river, as sediment travels from the upper to lower course it becomes both smaller and finer.

Question 4

Compare hydraulic action with abrasion.

Answer 4

Abrasion is the process when the current of the river will pick up eroded rocks and smash and rub them against the river bed or sides, this will result in them being eroded.
Hydraulic Action is the process were water and air are trapped within cracks in the river channel, the repetition of this process and the exertion of continual pressure on the cracks will cause them to break up.

Question 5

Define Weathering.

Answer 5

The erosion or wearing away of rocks within a river through biological, chemical or freeze-thaw weathering.

Question 6

Compare freeze-thaw weathering and biological weathering.

Answer 6

Freeze-thaw Weathering, this is the weathering process were rainwater will drain into cracks. As the temperature drops below 4°C it expands by at least 10%. This puts pressure on the rock, then as the temperature returns to normal it relieves the pressure. This continuation of the process can lead to further erosion.
Biological Weathering: Animals and the roots of plants will burrow into the rocks, this will lead to pressure being exerted onto the rocks and for them to slowly break up.

Question 7

Compare traction and suspension transport.

Answer 7

Traction is the rolling movement of large particles, like boulders, along the river bed under the force of the water within the river.
Suspension is transportation process were small particle like silt and clay are carried along by the water, they are in suspension.

Question 8

Waterfall Formation - Upper Course

Answer 8

When a river moves from a band of hard rock to soft rock it will erode the softer rock at a much quicker pace. This will lead to a ledge being created and a plunge pool forming at the bottom, then the ledge will collapse. The continual retreat will create a gorge.

Question 9

V-Shaped Valleys and Interlocking Spurs - Upper Course

Answer 9

The river, while in the upper course, will have much more vertical power, this will create a deep channel. Over time the sides will erode into the river through weathering. Interlocking Spurs are created because the river has very little lateral erosion power so must weave through bands of hard rock, thus creating a “zig-zag” pattern.

Question 10

Meanders - Middle Course

Answer 10

The helicoidal movement of water means that the inside of a bend will will receive less erosion than the outside. This causes the outside bend to continue to erode outwards, creating a wider bend and causing the river to migrate downstream.

Question 11

Ox-Bow Lakes - Middle Course

Answer 11

The continuation of erosion of a bend will lead to the creation of a narrow neck, when this is eroded through the meander will be sealed off with sediment and slowly infilled by deposition.

Question 12

Floodplains - Lower Course

Answer 12

When a river floods it slows down and deposits sediment, along with meanders migrating, this creates a plain which is vulnerable to flooding.

Question 13

Levees - Lower Course

Answer 13

When a river floods deposited material, the heaviest, creates a natural embankment, a levee, along the edge of the channel.

Question 14

Delta - Lower Course

Answer 14

Rivers are forced to slow down when they reach the sea or an ocean. They subsequently deposit material and this forces the water into smaller channels, distributaries, eventually the deposited materials creates low-lying land called a delta.

Question 15

Explain two ways climate, geology and slope processes change the river landscape.

Answer 15

Climate:
Low temperatures, this will lead to less evaporation and a greater discharge for erosion.
It will also lead to freeze-thaw Weathering occurring.
Geology:
Soft rock will erode at a quicker rate and can create landscapes such as waterfalls.
Hard rock will erode less, especially in the upper course, leading to the formation of interlocking spurs.
Slope Processes:
Both mass movement and slumping can lead to a greater quantity of sediment entering the river.

Question 16

Key features of a hydrograph.

Answer 16

Peak Rainfall:
When the heaviest rainfall occurred.
Peak Discharge:
The time with the highest river discharge.
Lag Time:
The time taken between the peak rainfall and the peak discharge.
Rising Limb:
The river level is rising.
Falling Limb:
The river level is falling.

Question 17

Compare a flashy and subdued hydrograph.

Answer 17

A flashy hydrograph will have a very steep rising limb and a very short lag time, it will usually also have a higher peak discharge and will probably lead to a flood.
A subdued hydrograph will have a gentle rising limb and a very long lag time. It is also probable that the river wouldn’t have flooded, there would have been less discharge.

Question 18

Explain how physical factors can affect flood hydrographs.

Answer 18

Physicals factors could lead to a increase of surface run-off, which leads to greater discharge and flooding, this could be from certain unsaturated soils and impermeable rock, along with mountainous terrain. Also if the antecedent conditions have been exceptionally harsh it will lead to a greater peak discharge event.

Question 19

Explain how human factors can affect flood hydrogrpahs.

Answer 19

All human factors have a similarity, it involves increasing surface run-off, be this through urbanisation and the increase of impermeable surfaces or through deforestation (less interception) and a change in land use (less infiltration or saturation) they all lead to greater surface run-off and river discharge.

Question 20

Explain how physical and human factos causes river flooding in the River Eden.

Answer 20

Physical Factors:
-Receives harsh South Western prevailing winds.
-Wet antecedent conditions (second wettest November ever).
-River levels were already high.
-Storm Desmond caused very heavy rainfall, 314 millimetres in 24 hours a UK record.
-The reservoirs overflowed.
-Acts as a drainage basin to the Lake District and Pennines.
-Impermeable rock is common in the area.
-Snowfall is common at that time of year.
Human Factors:
-Drainage ditches increased surface run-off to the river.
-Carlisle is a very urbanised and impermeable city.
-Issue with drainage capacity.
-Natural woodland had been deforested for farming.
-Parts of the basin had been drained for farming.
-Incorrect dredging procedure.

Question 21

What are the effects of flooding on people and the environment? What problems were caused?

Answer 21

Socio-Economic Effects:

• 3,000 homes destroyed in 2005, over 5200 in 2015.
• Residents had to live in temporary accommodation.
• Local services and businesses forced to close.
• Costs exceeded £500 million in 2015.
• Insurance claims topped £6 billion.
• Lots or livestock and farmland lost.
• Deterred tourists and increases insurance premiums.

Environmental Effects:

• River banks were eroded.
• Rivers were choked with debris and contaminated.
• Soils were eroded, habitats were destroyed.
• The saturated ground led to the decomposition of dead plants and animals, releasing noxious gases.