Rivers

Question 1

Dams

Answer 1

Dams + reservoirs. Dams are barriers and reservoirs are artificial lakes. Reservoirs store water and generate Hydroelectric power. Dams are expensive, creating a reservoir can flood existing settlements. Farmland downstream can become less fertile.

Question 2

Channel Straightening

Answer 2

Meanders are removed by buildings straight, artificial channels. Water leaves the area quickly, so flood risk is lower. Flooding can happen downstream though, faster moving water can cause more erosion downstream.

Question 3

Embankments

Answer 3

Raised walls are built along river banks. The river can hold more water, so floods are less frequent. They’re expensive, and a risk of flooding if water level rises.

Question 4

Flood relief channels

Answer 4

Channels built to divert water around built-up areas or to divert excess water if the river level gets too high. Gates on the channels mean that the release of water can be controlled, reducing flood risk. There will be increased discharge where the relief channel rejoins the river, which could cause flooding in that area

Question 5

Flood warnings and preparation

Answer 5

Give people time to move possessions. But don’t actually prevent floods.

Question 6

Flood plain zoning

Answer 6

Planting trees in river valley increases interception of rainwater. Discharge and flood risk decrease. Vegetation reduces soil erosion in the valley and provides habitats for wildlife. Less land available for farming.

Question 7

River restoration

Answer 7

Making river more natural, removing man made levees for example. Discharge is reduced, Less chance of flooding downstream. Little maintenance is needed and there are better habitats for wildlife. Local flood risk can increase especially if nothing is done to prevent major flooding

Question 8

Upper Course of a River has:

Answer 8

• Steep Gradient
• V-Shaped Valley
• Steep Sides
• Narrow, shallow channel

Question 9

Middle course of a river has:

Answer 9

• Medium Gradient
• Gently sloping valley dies
• Wider, deeper channel

Question 10

Lower course of a river has:

Answer 10

• Gentle gradient
• Very wide, almost flat valley
• Very wide, deep channel.

Question 11

Vertical Erosion:

Answer 11

• Deepens the river valley and channel, making it V-Shaped.
• Happens in the upper course
• High turbulence causes the rough, angular particles to be scraped along the river bed, causing intense downwards erosion.

Question 12

Lateral Erosion:

Answer 12

• Widens the river valley and channel during the formation of meanders.
• Dominant in middle and lower courses of a river.

Question 13

Hydraulic Action:

Answer 13

• The force of the river weather colliding with rocks breaks rock particles away from the river channel.

Question 14

Abrasion:

Answer 14

• Eroded rocks picked up by the river scrape and rub against the channel, wearing it away.

Question 15

Attrition:

Answer 15

• Eroded rocks picked up by the river crash into each other and break into smaller fragments.
• Their edges get rounded off 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.

Question 16

Solution (erosion):

Answer 16

• River Water dissolves some types of rock like chalk and limestone.

Question 17

Traction:

Answer 17

• Large particles like boulders are pushed along the river bed by the force of the water.

Question 18

Saltation:

Answer 18

• Pebble-sized particles are bounced along the river bed by the force of the water.

Question 19

Suspension:

Answer 19

• Small particles like silt and clay are carried along by the water.

Question 20

Solution (transportation):

Answer 20

• Soluble materials like limestone dissolve in the water and are carried along.

Question 21

When does deposition occur?

Answer 21

• When a river loses velocity and energy.

Question 22

Why do rivers slow down and deposit material?

Answer 22

• Volume of water falls
• Amount of eroded material increases
• River is shallower e.g on inside of a bend
• River reaches its mouth

Question 23

How does particle size affect how far material is transported?

Answer 23

• Smaller particles are transported further and deposited closer to the river’s mouth.

Question 24

How do waterfalls form? (6 marks)

Answer 24

• They form where a river flows over an area of hard rock followed by an area of softer rock.
• The softer rock is eroded by hydraulic action and abrasion more than the hard rock, creating a ‘step’ in the river.
• As water flows over the step it erodes more and more of the softer rock.
• A steep drop is eventually eroded, which is called a waterfall.
• The hard rock is eventually undercut by erosion. It becomes unsupported and collapses.
• The collapsed rocks are swirled around at the foot of the waterfall where they erode the softer rock by abrasion. This creates a deep plunge pool.
• Over time, more undercutting causes more collapses. The waterfall retreats, leaving behind a steep-sided gorge.

Question 25

What are interlocking spurs?

Answer 25

• The hillsides that interlock with each other as the river winds around them.

Question 26

How do interlocking spurs form?

Answer 26

• In the upper course, most erosion is vertically downwards which creates steep-sided, v-shaped valleys.
• The rivers lack the power to erode laterally, so they have to wind around the high hillsides that stick out into their paths on either side.

Question 27

How do meanders form?

Answer 27

• The current is faster on the outside bend because the river channel is deeper.
• More erosion takes place on the outside bend, forming river cliffs.
• The current is slower on the inside bend because the river channel is shallower.
• So eroded material is deposited on the inside of the bend, forming slip-off slopes.

Question 28

What is the thalweg?

Answer 28

• The line of deepest water and fastest flow in a river channel.

Question 29

How do meanders form ox-bow lakes?

Answer 29

• Erosion causes the outside bends to get closer until there’s only a small bit of lands left between the bands called the neck.
• The river breaks through this land, usually during a flood and the river flows along the shortest course.
• Deposition eventually cuts off the meander forming an ox-bow lake.

Question 30

What is the flood plain?

Answer 30

• The wide valley floor on either side of a river which occasionally floods.

Question 31

How do flood plains form?

Answer 31

• When rivers flood, the water slows down, loses energy and deposits the material that it’s transporting. This builds up the flood plain.
• Meanders widen as they migrate across floodplains laterally.
• Over time, meanders also migrate downstream.
• The deposition that happens on the slip-off slopes of meanders also builds up the flood plain.

Question 32

What are levees?

Answer 32

• Natural embankments (raised banks) along the edges of a river channel.

Question 33

How do levees form?

Answer 33

• During a flood, eroded material is deposited over the whole flood plain.
• The heaviest material is deposited closest to the river channel, because it gets dropped first when the river slows down and loses energy.
• Over time, the deposited material builds up, creating levees along the edges of the channel.

Question 34

What are estuaries?

Answer 34

• Tidal areas where the river meets the sea.

Question 35

How do estuaries form?

Answer 35

• The river valley it at its widest at the river mouth and the land is close to sea level.
• The water is tidal (rises and falls each day).
• When the water floods over the banks of a river, it carries silt and sand onto the valley floor.
• As the tide reaches its highest point, the water moves slowly and his little energy, so it deposits sediment.
• Over time, more mud build up, creating large mudflats.
• At low tide, the wide, muddy banks are exposed.

Question 36

Upper Course Evidence:

Answer 36

• Waterfalls
• Symbol for a cliff (black, blocky lines)
• High lands
• Crosses lots of contour lines in a short distance (steep)
• Narrow (thin, blue line)
• Close contour lines and the valley floor is narrow (river is in a steep-sided, V-shaped valley).

Question 37

Lower course evidence:

Answer 37

• Low
• Doesn’t cross any contour lines so it’s very gently sloping
• River meanders across a large, flat area, which is the flood plain.
• Wide (thick, blue line)
• Large meanders (ox-bow lake may form here).