4B - River Processes and Pressures

Question 1

Define the term weathering and give the 3 types of weathering.

Answer 1

• Breakdown and decay of rock by natural processes.
• Physical, chemical and biological weathering.

Question 2

Define mass movement and give the 2 types of mass movement.

Answer 2

• Downslope movement of materials due to gravity.
• Soil Creep
• Slumping

Question 3

Describe the process of soil creep.

Answer 3

• Particles of soil move down a slope under the force of gravity, collecting at the bottom of the valley. The river then erodes this material.

Question 4

Name the 4 erosion processes.

Answer 4

• Hydraulic action
• Attrition
• Abrasion
• Solution

Question 5

Describe the process of abrasion.

Answer 5

• Material in the river rubs against beds and banks of the channel, eroding them.

Question 6

Describe the process of attrition.

Answer 6

• Sediment particles collide into each other, knocking of the edges of the sediment. Repeated attrition causes the sediment to become rounder and smaller.

Question 7

Give the 4 transportation processes in order of heaviest to lightest deposited material.

Answer 7

• Traction
• Saltation
• Suspension
• Solution

Question 8

ESQ - Explain how waterfalls are formed from the interaction of different processes. (4)

Answer 8

• The river erodes the less resistant rock, undercutting the hard rock (1)
• This causes an overhang, causing the hard rock to collapse (1)
• Force of water and abrasion by boulders forms a plunge pool (1)
• This process repeats as the waterfall continuously retreats, forming a gorge (1)

Question 9

Describe how a delta is formed.

Answer 9

• A river reaches a body of water, losing velocity and deposits sediment. When rivers deposit sediment faster than coastal processes erode it, sediment builds up into a delta. The river splits into distributaries.

Question 10

Describe the formation of an interlocking spur.

Answer 10

• Rivers near sources have little power so mainly erode downwards. The water flows around valley side slopes (spurs), which leaves them interlocking, with the valley overlapping with the spur.

Question 11

How is a levee formed?

Answer 11

• During floods, water and sediment come out of the channel due to overflowing. The river loses velocity and energy and deposits larger sediment on the banks. This process repeats to form a levee.

Question 12

Give the characteristics of the upper course of a river.

Answer 12

• High annual rainfall
• Large height above sea level
• Narrow, shallow channel
• Vertical erosion forming V-shaped valleys with steep slopes.
• Hard and impermeable rock

Question 13

Give the characteristics of the middle course of a river.

Answer 13

• Medium annual rainfall
• Softer and permeable rock
• Wider and deeper river channel
• Lateral erosion causing a wider and flatter valley
• Tributaries join river, increasing discharge

Question 14

Give the characteristics of the lower course of a river.

Answer 14

• Very soft and permeable rock
• Very wide and deep channel
• Less friction with river beds increase river’s velocity
• High sediment load, increasing deposition

Question 15

What does the rising limb show in a storm hydrograph?

Answer 15

• The rising water after rainfall

Question 16

State the definition of the lag time.

Answer 16

• Difference between time of heaviest rainfall and point at which the river contains the largest amount of water (peak discharge).

Question 17

What does the falling limb show?

Answer 17

• Discharge falling as less water reaches the channel.

Question 18

Give 2 processes which result in quick flows and a steeper hydrograph.

Answer 18

Geology - Impermeable rocks (granite) cannot absorb water.
Slopes and soil depth - Steeps slopes and thin soil cause rapid surface runoff.
Cities - Roads and roofs are impermeable, so water runs off quickly into rivers.

Question 19

Give 2 processes which result in slow flows and a flatter hydrograph.

Answer 19

Precipitation - Small amounts of rainfall or snow melt.
Antecedent conditions - If recent high rainfall has saturated the soil, infiltration is reduced, therefore surface runoff increases.
Slopes and soil depth - Gentle slopes and deep soil cause slower surface runoff.

Question 20

Explain what the Environment Agency do.

Answer 20

• Reduce the chances of flooding. Managing rivers and land use and building flood defences.
• Reduce impact of flooding. Help people prepare for floods and give flood warnings.

Question 21

ESQ - Describe the differences between soft and hard engineering. (2)

Answer 21

• Soft engineering uses natural techniques and are cheap and need little maintenance (1)
• Hard engineering uses man-made structures and are expensive and need lots of maintenance. (1)

Question 22

Give 3 examples of hard engineered structures and how they prevent flooding.

Answer 22

• Demountable flood barriers - Reduces the impact of a flood, and can be demounted when flood is averted.
• Embankments - Stops water spreading into vulnerable areas.
• Storm surge barriers - Protects from storm surges following on from a large flood.

Question 23

Give an example of 2 soft engineered structure and how they protect from floods. [4]

Answer 23

• Flood-plain retention [1] It allows flooding rivers to slow down flood waters [1]
• River restoration [1] works by restoring meanders, so they flood but slow down [1]

Question 24

What is a cost-benefit analysis used for?

Answer 24

• Comparing the cost of a project with the benefits it will bring.

Question 25

Explain 2 reasons why flood risks can increase. [4]

Answer 25

Changes to land use. Urban development creates impermeable surfaces [1] therefore increasing surface runoff [1]

Climate change. A warmer climate can cause ice caps to melt [1] therefore more sea water increases flood risk [1]

Question 26

Explain how a meander is formed by different processes [4]

Answer 26

Lateral erosion by the river forms an steep bank called a river-cliff [1]
Lateral erosion then forms a slip-off slope on the inside of the bend, which is gently sloping. [1]
Erosion and deposition deposits sediment onto the river-cliff and slip-off slope [1]
This causes a steep outside bend, and a gentle inside bend [1]