Rivers

Question 1

Drainage Basin

Answer 1

An area of land drained by a river and its tributaries

Question 2

Source

Answer 2

The start of a river

Question 3

Tributary

Answer 3

A stream or river that flows into a larger river

Question 4

Confluence

Answer 4

Where a tributary joins the river

Question 5

Long profile shape

Answer 5

Upper course - Steep gradient

Middle course - Gentle gradient

Lower course - Very gentle gradient

Question 6

Cross profile shape

Answer 6

Upper Course - Steep V-Shaped valley, narrow and shallow turbulent river

Middle Course - Valley with wider, flatter bed. Wider and deeper river

Lower Course - Very wide and flat valley. Wide, deep river with large sediment load

Question 7

Why does the cross profile change over the course of the river?

Answer 7

• More water joins from more tributaries
• So more energy to erode larger channel
• Through processes such as abrasion, hydraulic action, etc

Question 8

Why does velocity increase downstream?

Answer 8

• Upper course is shallower, so more energy is lost through friction between water and banks
• In the lower courses, water depth is greater so less water is in contact with the banks so river flows faster DESPITE SHALLOWR GRADIENT

Question 9

Hydraulic Action

Answer 9

Where the force of water breaks rock particles away from the river channel

Question 10

Abrasion

Answer 10

The eroding away of the river channel by rocks carried with the flow of the river

Question 11

Attrition

Answer 11

• Stones carried by river hit each other

- Breaking down and rounding eachother

Question 12

Solution / Corrosion

Answer 12

Mildly acidic river water dissolves limestone and chalk

Question 13

Traction

Answer 13

Large boulders and rocks are rolled along river bed

Question 14

Saltation

Answer 14

Small pebbles and stones bounce along river bed

Question 15

Suspension

Answer 15

• Small particles are carried along by the water

- Such as silt or clay

Question 16

Solution

Answer 16

Dissolved load

Question 17

Typical Landforms in each course

Answer 17

Upper course - Interlocking spurs, V-shaped valley, gorges, waterfalls

Middle course - Meanders, OX-bow lakes

Lower course - Levees, flood plains, river estuaries

Question 18

Interlocking spurs formation

Answer 18

1. V-Shaped valley created by erosion vertically downwards
2. Rivers aren’t powerful enough to erode laterally
3. So wind around the high hillsides in the way
4. Hillsides interlock as river winds round them
5. Interlocking spurs is formed

Question 19

Waterfall formation

Answer 19

1. River flows over hard rock lying on top of soft rock
2. River erodes soft rock faster, developing a vertical drop where hard rock and soft rock meets
3. Plunge pool forms from force of falling water (hydraulic action)
4. Rock above plunge pool is undercut and left hanging
5. Overhanging hard rock eventually collapses due to force of gravity
6. Erosion continues to undercut underneath the hard rock
7. So the process repeats and the waterfall over time retreats upstream

Question 20

Gorge formations

Answer 20

• Waterfall retreats upstream
• Leaving narrow, steep sided valleys called GORGES
• Also form at the end of glacial periods from meltwater

Question 21

Meander

Answer 21

• Wide bend in the river found mainly in lowland areas

- Most efficient course of river in gentle slopes

Question 22

Meander formation

Answer 22

• water levels travel faster on the outside of the bend
• so more lateral erosion takes place
• widening meanders
• deposition also occurs mainly in the insides of the bend

Question 23

What are pools

Answer 23

Deep water found on the outside of bends (faster flow, more vertical Erosion)

Question 24

What are riffles

Answer 24

Riffles are shallow pools of water formed by the deposition of coarse sediment

Question 25

Ox-bow lake formation

Answer 25

1. Meander is created 2. Erosion through hydraulic action bends river so that the meanders travel towards each other 3. The neck of the meander eventually breaks creating a straight river 4. The old meander becomes blocked from the main river by deposition, creating a separate ox-bow lake

Question 26

Deposition

Answer 26

- Deposition is the dropping of the river’s load - when the water velocity decreases so does not have enough energy to transport the sediment - occurs mainly in the lower course of the river

Question 27

Floodplain

Answer 27

Wide flat area of marshy land on either side of the river - occurs mainly in middle and lower courses

Question 28

Levee

Answer 28

An enlarged bank built up on each side of the river by deposition during river flooding

Question 29

Estuary

Answer 29

The tidal mouth of a large river, where tide meets the stream - a transitional zone between fluvial and coastal processes

Question 30

Physical factors affecting flood risk

Answer 30

Precipitation - high amounts of rain can cause rivers to flood Geology - impermeable rocks force water to flow, decreasing lag time and increasing flood risk because ground cannot absorb water Relief - steeper mountain environments cause rapid flow of water

Question 31

Lag time

Answer 31

The time between the peak rainfall and peak discharge

Question 32

Human factors affecting flood risk

Answer 32

Urbanisation- impermeable surfaces such as roads aid water flow and decrease lag time Deforestation - less interception of water, lag time increases and aids water flow Agriculture - increased surface runoff from unused soil

Question 33

What are hydrographs

Answer 33

Graph plotting river discharge measured in cumecs, against against time after a storm

Question 34

Hard engineering strategies

Answer 34

- dams / reservoirs regulate water flow (eg. Clywedog reservoir) - by-pass channels to cut through meanders to reduce flood risk through urbanised areas - channel straightening lined with concrete for faster flow of water through urbanised areas - channel enlarged by dredging

Question 35

Costs / benefits of channel straightening

Answer 35

- can reduce risk for vulnerable areas - however shifts problem downstream - creates an unnatural environment, destroying riverside habitats

Question 36

Flood relief channels

Answer 36

- Building new artificial channels which are used when a river is close to maximum discharge - take pressure off main channels when floods are likely - thus reducing flood risk - eg. Jubilee Rivee

Question 37

Soft engineering strategies

Answer 37

- afforestation to increase interception of water - Wetland areas used for water storage - river bank conservation, eg. Planting trees - flood warning / preparation