Section C - River Landscape

Question 1

What are the inputs and outputs in a Hydrological Cycle?

Answer 1

Inputs- Precipitation

Outputs- Evaporation, Transpiration, River Flow to the Sea

Question 2

What are the flows in a Hydrological Cycle?

Answer 2

Flows- Infiltration, Percolation, Through Flow, Groundwater Flow, Surface Runoff

Question 3

What are the stores in a Hydrological Cycle?

Answer 3

Stores- Interception, Surface Storage, Soil Moisture, Ground Water

Question 4

Name and explain the 4 types of river erosion processes.

Answer 4

Hydraulic Action- The force of the river water colliding with rocks breaks rock particles away from the river channel.
Abrasion- Eroded rocks picked up by the river scrape and rub against the channel, wearing it away. Most erosion happens by abrasion.
Attrition- Eroded rocks picked up by the river crash into each other and break into smaller fragments. Their edges also get rounded as they rub together. The further material travels, the more it is eroded - attrition causes particle size to decrease from a river’s source to its mouth.
Solution- River water dissolves some types of rock, e.g. chalk and limestone.

Question 5

Name and explain the 4 types of river transportation processes.

Answer 5

Traction- Large particles like boulders are pushed along the river bed by the force of the water.
Saltation- Pebble sized particles are bounced along the river bed by the force of the water.
Suspension- Small particles like silts and clay are carried along by the water.
Solution- Soluble materials (e.g. limestone) dissolve in the water and are carried along.

Question 6

What are the two upper course features?

Answer 6

Waterfall/Gorge and V-shaped Valleys/Interlocking Spurs

Question 7

Explain how waterfalls and gorges are formed.

Answer 7

Waterfall / Gorge- Waterfalls form where a river flows over an area of hard rock followed by an area of soft rock and since soft rock erodes quicker it creates a plunge pool. As the waterfall retreats, this leaves back a gorge.

Question 8

Explain how V-shaped Valleys and Interlocking Spurs formed

Answer 8

V-shaped Valleys / Interlocking Spurs- In the upper course of a river most of the erosion is vertically downwards, this creates steep v-shaped valleys. The river lacks the energy to erode laterally, so it winds around the high hillsides.

Question 9

What are the two middle course features?

Answer 9

Meanders and Ox-bow lake

Question 10

Explain how Meanders are formed

Answer 10

Meanders-Rivers develop large bends called meanders in their middle and lower courses, in areas where the channel has both shallow and deep sections.

Question 11

Explain how Ox-bow lakes are formed

Answer 11

Ox-bow Lakes- Erosion causes the outside bends to get closer until it forms a small piece of land left called a neck then the river breaks through the land during a flood and flows along the shortest course causing deposition to eventually cut off the meander forming an ox-bow lake like the ones in River Calder

Question 12

What are the three lower course features?

Answer 12

Levees, Floodplain, Estuaries

Question 13

Explain how Levees are formed.

Answer 13

Levees- are natural embankments found along a channel edge where heavy material is deposited during a flood on the edges and this process repeats until forming Levees

Question 14

Explain how floodplains are formed

Answer 14

Floodplains- are wide flat areas of land that flood

Question 15

Explain how estuaries are formed

Answer 15

Estuaries- found at the river mouth where the river meets the sea. At high tides, silt and sand are carried onto the valley floors and at low tides, it reveals the mudflats

Question 16

River Jubilee Case Study- Location?

Answer 16

The Jubilee River is a relief channel for the River Thames in southeast England. The relief channel runs through Berkshire and Buckinghamshire, flowing roughly parallel to the River Thames.

Question 17

River Jubilee Case Study- Purpose?

Answer 17

This area of the Thames flood plain is low-lying and prone to flooding. The impermeable surfaces of the built-up areas have historically resulted in flooding following high rainfall events. Given the high-value property in this area, the EA decided to increase the level of flood protection.

Question 18

River Jubilee Case Study- Explain this strategy of the flood relief channel.

Answer 18

The Jubilee River was created to take overflow water from the River Thames in times of high discharge following heavy rainfall.

Question 19

River Jubilee Case Study- Economic Benefits and Issues

Answer 19

The weirs in the river were damaged after 1 year and had to be repaired for £680,000. At a projected cost of £330 million, the Jubilee River was one of four flood-relief channels planned for the lower course of the Thames. However, the EA ran short of funds. If further engineering is to alleviate flooding downstream, local councils and businesses will have to make up a £110 million shortfall. Is this fair, when Windsor and Eton residents did not have to pay? Until a solution is found, small businesses such as shops stand to lose money, as they cannot open when their premises are flooded. Insurance costs are high.

Question 20

River Jubilee Case Study- Environmental Benefits and Issues

Answer 20

In 2014, there was extensive flooding immediately downstream from where the flood-relief channel rejoined the Thames. The built environment suffered from flooded roads and buildings. Fields were inundated and habitats were disturbed. The concrete weirs are rather ugly, especially under normal flow conditions, when more concrete is exposed. Ongoing repair work has made the matter worse, such as at Manor Farm Weir. There is also the problem of algae collecting behind the weirs. This disrupts the natural ecosystem.

Question 21

River Jubilee Case Study- Social Benefits and Issues

Answer 21

3000 Wealthy houses protected. The Thames at Old Windsor now suffers from a much higher discharge due to the merging of the two channels just upstream. 2014 flood showed this.

Question 22

What are the 4 Hard Engineering and the 4 Soft Engineering methods in River Management?

Answer 22

Hard- Dams and Reserviour, Channel Straightening, Embankments, Flood-relief channels
Soft- Flood Warnings and Preparations, Flood plain Zoning, Planting Trees, River Restoration.

Question 23

Explain Dams and Reserviour and mention the Benefits and Disadvantages

Answer 23

What is it- Dams are barriers built usually in the upper course. A reservoir is an artificial lake behind the dam
Benefits- Reserviours store water, control water flow and prevent floods downstream. Also used for hydroelectric power HEP
Disadvantage- Is Expensive and reservoirs can flood existing settlements. Materials are deposited in reservoirs so farmland downstream can become less fertile.

Question 24

Explain Channel Straightening and mention the Benefits and Disadvantages

Answer 24

What is it- Meanders are removed to build straighter channels
Benefits- Water leaves more quickly rather than building up so flood risk is lower
Disadvantage- Flooding may happen downstream and fast-moving water increases erosion downstream

Question 25

Explain Embankments and mention the Benefits and Disadvantages

Answer 25

What is it- raised walls are built along river banks
Benefits- river can hold more water so flooding is less frequent
Disadvantage- Quite expensive and there is a risk of severe flooding if water rises over embankments or it breaks

Question 26

Explain Flood-relief Channels and mention the Benefits and Disadvantages

Answer 26

What is it- Channels built to divert water away from built-up areas or divert excess water
Benefits- Gates on the channel mean the release of water flow can be controlled, reducing flood risk
Disadvantage- Increase discharged where rivers connect causing flooding in that area

Question 27

Explain Flood Warnings and Preparations and mention the Benefits and Disadvantages

Answer 27

What is it- EA issues flood warnings, Buildings are modified to minimise flood damage, Residents can prepare sandbags and flood boards prior to the flood
Benefits- WArnings give people time to move valuables and evacuate reducing the impact of flooding
Disadvantages- WArnings don’t prevent floods, People may not have access to warnings, Modifying buildings is expensive, Preparations don’t guarantee safety from floods and it could give people a false sense of security

Question 28

Explain Flood plain Zoning and mention the Benefits and Disadvantages

Answer 28

What is it- Restrictions prevent buildings on part of floodplains likely to flood
Benefits- fewer impermeable surfaces reducing flood risk and the impact of flooding is reduced as with no buildings there will be no damage
Disadvantage- Expansion of urban areas is limited. It can’t help areas with buildings already.

Question 29

Explain Planting Trees and mention the Benefits and Disadvantages

Answer 29

What is it- Planting trees in valley increases interception of water and lag time
Benefits- Discharge and flood risk decrease. Vegetation reduces soil erosion and provides habitats for wildlife
Disadvantage- Less land available for farming

Question 30

Explain River Restoration and mention the Benefits and Disadvantages

Answer 30

What is it- making the river more natural so the flood plain can flood naturally
Benefits- Discharge is reduced so there is less risk of flooding downstream, little maintenance and better habitats for wildlife
Disadvantage- Local flood risk increases especially if nothing is done to prevent major flooding

Question 31

Name and explain the four factors that affect flood risk.

Answer 31

Heavy Rainfall - Water arrives too quickly to infiltrate the ground.
Prolonged rainfall - Prolonged rainfall saturates the soil
Geology - Clay soil and some rocks such as granite are impermeable.
Relief - If a river is in steep-sided valley water will reach the river quicker.

Question 32

What is a Hydrograph?

Answer 32

A hydrograph shows how a river’s discharge changes in response to a precipitation event. The vertical axis measures precipitation (usually rainfall) in millimetres and discharges in cubic metres per second (cumecs). The horizontal axis measures time, usually in hours or days. The bars represent rainfall and the line graph shows discharge.

Question 33

What are the 7 main features of a Hydrograph?

Answer 33

Peak Rainfall, Rising Limb, Peak Discharge, Lag time, Falling Limb, Base Flow, Bankfull Discharge.

Question 34

What is a Peak Rainfall of a Hydrograph?

Answer 34

Peak rainfall: the highest amount of rainfall per time

unit (the highest bar)

Question 35

What is a Rising Limb of a Hydrograph?

Answer 35

Rising limb: shows how quickly the discharge rises

after a rainstorm (the first part of the line graph)

Question 36

What is a Peak Discharge of a Hydrograph?

Answer 36

Peak discharge: the highest recorded discharge

following a rainfall event (the top of the line graph)

Question 37

What is a Lag Time of a Hydrograph?

Answer 37

Lag time: the time difference between peak rainfall
and peak discharge (measure the horizontal distance
between the top of the highest rainfall bar to the top
of the discharge line and note the difference in hours)

Question 38

What is a Falling Limb of a Hydrograph?

Answer 38

Falling limb: shows the reduced discharge once the
main effect of runoff has passed (the last part of the
line graph which is going down)

Question 39

What is a Base Flow of a Hydrograph?

Answer 39

Base flow: the normal flow of a river when its water
level is being sustained by groundwater flow (usually
shown on the hydrograph as a separate line)

Question 40

What is a Bankfull Discharge of a Hydrograph?

Answer 40

Bankfull discharge: (does not always appear on
hydrographs) will be drawn as a horizontal line
marking the level of discharge above which flooding
will occur as the river will burst its banks