Rivers

Question 1

Define Weathering

Answer 1

The breakdown and decay of rock by natural processes in situe

Question 2

Describe Mechanical Weathering

Answer 2

aka Freeze-Thaw weathering
Rainwater gets into cracks in rocks and freezes if temperatures drop below zero. The water expands as it turns to ice and then exerts a pressure on the rock, causing it to break into smaller pieces.

Question 3

Describe Chemical Weathering

Answer 3

aka Acid Rain
All rain is slightly acidic, if the air is polluted by factories and vehicles, the rain can become more acidic. When this rain falls on rocks, the acid reacts with the weak minerals, causing them to dissolve and the rock to decay

Question 4

Describe Biological Weathering

Answer 4

Plant roots grow into cracks in rocks, splitting them apart

Question 5

Define Mass Movement

Answer 5

The movement of rocks and soil downslope due to gravity (helped by weaker rocks, steep slopes and heavy rainfall)

Question 6

Describe Sliding

Answer 6

Material moves rapidly downslope in one go

Question 7

Describe Slumping

Answer 7

Material moves rapidly downslope in one go, rotating as it moves

Question 8

How is the slope of rivers made steeper?

Answer 8

Material moves down the valley sides by mass movement and collects at the bottom where it’s eroded by a river, this makes it steeper causing more mass movement

Question 9

What conditions do rivers have when they have the most energy?

Answer 9

Large amount of water, steep gradient

Question 10

Define River Erosion

Answer 10

The action of water wearing away the rocks and soils on the valley bottom and sides

Question 11

Describe Hydraulic Action (rivers)

Answer 11

Sheer force of of the water hitting the river bed and banks and wearing them away

Question 12

Describe Abrasion (rivers)

Answer 12

Material carried in the river rubs against bed and banks of the channel, wearing them away

Question 13

Describe Solution (rivers)

Answer 13

River water is slightly acidic, so it can dissolve some rocks and minerals in contact with the river (Limestone and chalk mostly affected)

Question 14

Describe Attrition (rivers)

Answer 14

Sediment particles carried in the river collide with each other. Continued collision of particles causes them to become rounder and smaller downstream.

Question 15

Define River Transport

Answer 15

River picks up and carries material as it flows downstream

Question 16

Describe Deposition (rivers)

Answer 16

Occurs when a river no longer has enough energy to carry its load. As the river’s discharge and velocity reduce, the heaviest material is deposited first - e.g. after flooding

Question 17

Describe Traction (rivers)

Answer 17

Stones roll along the river bed

Question 18

Describe Saltation (rivers)

Answer 18

Sand-sized particles bounce along the river bed

Question 19

Describe Suspension (rivers)

Answer 19

Silt and clay-sized particles are carried within the water flow

Question 20

Describe Solution (rivers)

Answer 20

Some minerals dissolve in the water

Question 21

Order the river transport processes from most to least energy required

Answer 21

Traction (most energy)
Saltation
Suspension
Solution (least energy)

Question 22

Explain the Upper Course of Rivers

Answer 22

High rainfall
Vertical erosion leads to V-shaped valleys and interlocking spurs
Hard rock on top of softer rocks forms waterfall and gorges
Main land use around is for recreation and forestry

Question 23

Explain the Middle Course of Rivers

Answer 23

Vertical/lateral erosion so meanders form on valley floors which help to widen the valley floors
Wider valley floors used for crops
Steeper valley sides used for sheep farming

Question 24

Explain the lower course of rivers

Answer 24

Lateral erosion
River flows more rapidly so meanders form oxbow lakes
Deposition forms flood plains and levees

Question 25

How do rivers change from the upper to lower course? (brief)

Answer 25

Bradshaw model shows…
- Gradient reduces as you move to lower course
- Width Increases as you move to the lower course
- Width, velocity and discharge increase as you move to lower course
- Sediment size decreases as you go down river due to attrition taking place

Question 26

Explain the formation of Interlocking Spurs

Answer 26

Near the source, rivers are small and don’t have a lot of power. So, they flow around valley side slopes, called spurs, rather than being able to erode them. The spurs are left interlocking (those from one side of the valley overlapping with spurs from the other side)

Question 27

Explain the formation of Waterfalls - and Gorges

Answer 27

• waterfall is formed along a river when a band of hard, more resistant rock lies over a band of soft rock
• the river erodes the less resistant rocks at a faster rate, gradually undercutting the more resistant rock
• eventually, the hard rock cannot support its own weight and collapses under gravity
• the force of the fall water and abrasion by large angular boulders leads to erosion of the river bed forming a plunge pool
• the soft rock continues to be eroded and the hard rock collapses so a steep-sided gorge is formed as the waterfall retreats upstream
• gorges form in hard rocks where vertical erosion by rivers is dominant

Question 28

How are river cliffs formed?

Answer 28

River cliffs are formed on the outside bend of a river as the river laterally erodes and undercuts the bank

Question 29

Define a Meander

Answer 29

Meanders are bends in a river’s course commonly found on a river’s flood plain

Question 30

Explain the formation of Meanders and its features

Answer 30

• Flow of the water swings from side to side, directing the line of maximum velocity and force of the water towards the outside of the bend
• This results in lateral erosion by undercutting and an outer, steep bank is formed called a river cliff
• On the inside of the bend the velocity and force of water is less, leading to deposition and the formation of a gently sloping bank called a slip-off slope
• The material deposited is called a point bar (curved in shape)

Question 31

Why are Meanders asymmetrical?

Answer 31

Erosion (outside) and deposition (inside) - steep on outside, gentle slope on inside

Question 32

Explain the formation of flood plains

Answer 32

They form due to both erosion and deposition. Erosion removes any interlocking spurs, creating a wide, flat area on either side of the river. During a flood, material being carried by the river is deposited (as the river loses its speed and energy to transport material). Over time, the height of the floodplain increases as material is deposited on either side of the river.

Question 33

Explain the formation of Levees

Answer 33

• Levees occur in the lower course of a river when there is an increase in the volume of water flowing downstream and flooding occurs. Sediment that has been eroded further upstream is transported downstream.
• When a flood occurs, the river loses energy. The largest material is deposited first on the sides of the river banks and smaller material further away.
• After many floods, the sediment builds up to increase the height of the river banks, meaning that the channel can carry more water (a greater discharge) and flooding is less likely to occur in the future.

Question 34

Explain the formation of Oxbow Lakes

Answer 34

• Erosion narrows the neck of the land within the meander and as the process continues, the meanders move closer together.
• When there is a very high discharge (usually during a flood), the river cuts across the neck, taking a new, straighter and shorter route. Deposition will occur to cut off the original meander, leaving a horseshoe-shaped oxbow lake.

Question 35

What are the physical causes of Flooding? - describe each one

Answer 35

Intense Rainfall - Soil and rocks quickly become saturated. As infiltration is reduced, water flows over the surface and into rivers a a faster rate

Duration of rainfall - Soil becomes saturated, preventing further infiltration of rainwater leading to increased surface runoff

Snow melt - Occurs in places where a lot of snow falls in the winter months. When temperatu7res rise above zero in the spring, the snow that has built up melts, releasing large volumes of meltwater

Rocks - Impermeable rocks (e.g. clay) don’t allow water to pass through them, so rainwater will run off the surface and straight into the river channel

Relief - Water reaches the river channel much faster where slopes are steeper

Question 36

What are the Human causes of flooding? - describe each one

Answer 36

Deforestation - vegetation collects, stores and uses water from rainfall (called inception). Plant roots encourage water to pass into soil and rock, so vegetation reduces runoff. If it is removed, more water can reach the river channel more quickly

Urbanisation - Towns and cities have impermeable surfaces like concrete and tarmac that rainwater can’t infiltrate. So, this causes the water to immediately run off into river channels

Question 37

Why does sediment size decrease downstream?

Answer 37

Downstream there is higher energy and discharge which increases the rate of erosion for processes like attrition which decreases sediment size

Question 38

How does the weather/climate effect river erosion?

Answer 38

Increased rainfall leads to more water in the river, leading to increased rates of erosion and chemical weathering

Increased temperatures may effect biological weathering (photosynthesis effected by sunlight, more/less roots grow into rocks breaking them apart)

Question 39

How does the weather/climate effect Mass movement?

Answer 39

Heavy rain increases mass movement

Question 40

How does weathering effect Mass Movement?

Answer 40

Weathering weakens rocks making it easier for them to be transported by mass movement

Question 41

How does erosion effect Mass Movement?

Answer 41

erosion at the base of cliffs and valleys means they have no support, encouraging mass movement

Question 42

What are the effects of flooding on Humans?

Answer 42

Social: Houses flooding, people become homeless and costs money to repair
Economic: Cost of businesses post flood
Environmental: Damage to landscapes and pollution

Question 43

What are the advantages and disadvantages of hard-engineering river flood defences?

Answer 43

Channelisation: Involves deepening/straightening the river
ADVANTAGES - Allows more water to run through the channel more quickly, taking it away from places at risk
DISADVANTAGES - Water taken downstream may put other places at risk, it doesn’t look natural

Dams and Reservoirs: Barriers constructed to hold back water in artificial lakes
ADVANTAGES - Long-lasting, can provide a local water supply, can be used for water sports
DISADVANTAGES - Expensive, can ruin the environment, some lakes suffer from growth of algae

Question 44

What are the advantages and disadvantages of soft-engineering river flood defences?

Answer 44

Washlands: Areas on the flood plain that are allowed to flood
ADVANTAGES - Give a safe place for flood water to go and help slow floodwaters down, restores soil structure in the flood plain, making it more efficient at storing water
DISADVANTAGES - Allowing land to flood may mean a change in land use such as farmland

Flood Plain Zoning: Governments allocate areas of land to different uses, according to their level of flood risk
ADVANTAGES - Flood risk management aims to prevent building homes and businesses in high risk flood zones and put less valuable places there instead such as open football pitches
DISADVANTAGES - May not be the best places to build sporting grounds as may be difficult to access for the public