Rivers

Question 1

Tributaries

Answer 1

Smaller rivers that join main river

Question 2

Confluence

Answer 2

Point at which rivers meet

Question 3

Drainage basin

Answer 3

Land drained by a river system

Question 4

Watershed

Answer 4

Boundary of the drainage basin, usually made up of highland

Question 5

Discharge

Answer 5

Amount of water passing a specific point at a given time and is measured in cabin meters per scene (dependent on river’s velocity and volume)

Question 6

Volume

Answer 6

Amount of water in the river

Question 7

Velocity

Answer 7

Speed of the river

Question 8

River channel

Answer 8

The area in which a river flows

Question 9

Describe the changes in a river valley from source to mouth

Answer 9

upper course: main process is vertical erosion, is steep sided, narrow, v shaped, lined with boulders, large wetted perimeter, low velocity, low discharge
middle and lower course: sides are less steep, gradient decreases, shape changes from a V to a U, wider, faster velocity, higher discharge (dominant process in middle course is lateral erosion, this increases rate of erosion by hydraulic action and abrasion and dominant process in lower course is deposition)

Question 10

V-shaped valley

Answer 10

river has the power to erode downwards as it is way above the sea. valley sides are steep due to soil and loose rock being washed downhill following heavy rainfall.

Question 11

Discharge

Answer 11

Depends on river’s velocity and volume in the channel. Velocity depends on friction (wetted perimeter) and volume depends on the amount of water reaching the channel either though tributaries or groundwater flow

Question 12

Why narrow and shallow channel in upper course?

Answer 12

As discharge is low, power of erosion is reduced

Question 13

Why steep gradient in upper course?

Answer 13

Harder geology= more resistant to erosion

Dominant process is vertical erosion with means it cuts into rock which leads to a steeper profile

Question 14

Why does discharge increase downstream?

Answer 14

Velocity increases due to reduced friction as a result of reduced wetted perimeter (smoother channel)

Question 15

Hydraulic action

Answer 15

Pressure of water pushing against bank and bed of the river. Includes air compressing into cracks which means more pressure-> rock breaks

Question 16

Corrosion (solution)

Answer 16

Acids in river dissolve rocks

Question 17

Abrasion

Answer 17

Particles (load) carried by river and thrown against banks with force, they wear the bed and banks down

Question 18

Attrition

Answer 18

Rocks in the upper course roll around and knock each other until smooth pebbles or sand are formed

Question 19

How does mass movement impact river landscapes

Answer 19

mass movement causes river banks to be washed into the river. Soil creep creates a rippled effect/ causes soil to slowly slide into the river. Slumping, due to saturation of banks, leads to the rotational movement of river banks. Impacts: loss of land, damage to property, damage to river defences, flooding and river blockage

Question 20

How is a V shaped valley formed

Answer 20

Upper course river is small, water mostly contacts the bed and banks -> lots of friction, river flows slowly. Most energy used to overcome friction. Rest of energy used to erode downwards (vertical erosion) -> v shaped valley. As river winds its way down between berries of more resistant rock, interlocking spurs are formed

Question 21

Transportation

Answer 21

Traction, saltation, suspension and solution

Question 22

Traction

Answer 22

Rolling Stones along the bed

Question 23

Saltation

Answer 23

Small particles bounce along bed in a leapfrog motion

Question 24

Suspension

Answer 24

Silt and clay sized load are thrown through the water flow

Question 25

Solution

Answer 25

Minerals dissolve in water

Question 26

Deposition

Answer 26

When a river lacks the energy to carry its load; it begins with the heaviest particles, it happens when there is less water or where the current slows down. Large boulders are deposited at the top and very small particles are deposited at the end -> sorting

Question 27

Waterfalls

Answer 27

They occur because the river flows over hard rocks which erodes slowly. Beneath is softer rock which is eroded faster to form a 'step'. Force of water erodes the bottom of the waterfall to form a plunge pool. Hard rock gets undercut as the soft rock erode so that it eventually collapses.

Question 28

Meanders and OxBow lakes

Answer 28

In the middle course of river there is more energy and a high volume of water. Gradient here is gentle. As river erodes laterally, to the right side then left, it forms large bends, and the horse shoe like loops called meanders. This formation is due to both deposition and erosion. They gradually migrate downstream. The force of the water erodes and undercuts the river banks on the outside of the bend as there is more friction. Overtime the horseshoe becomes tighter until the ends become very close together. As the river breaks through, e.g during a flood, the river has more energy and the ends join, the loop is cut off from the main channel and this is called an ox bow lake

Question 29

Deltas

Answer 29

Deltas occur where a river that carries a large amount of sediment meets a lake or the sea. This meeting causes the river to lose energy and drop sediment it's carrying. Deltas form where river mouths become choked with sediment, causing the main river channel to split into hundreds of smaller channels or distributaries.

Question 30

Levées

Answer 30

When a river floods, the coarsest material is deposited first, on the edges of the river, forming a natural embankment called a levée. Deposition happens due to increase in friction when river comes into contact with the bed meaning that energy is lost

Question 31

Flood plain

Answer 31

Area of alluvial deposits found beside the river in its lower course. As meanders move slowly downstream they erode away the valley to create a wide valley floor, they deposit layers of alluvial material on the slip off slope, building up into a large flood plain

Question 32

Flooding and prevention

Answer 32

Flooding occurs when a river gets more water than its channel can hold. Can be prevented by building houses on stilts, being prepared, evacuation ready, government awareness, education, building dams or embankments

Question 33

Case study: what are the human and physical causes of river flooding?

Answer 33

Physical: impermeable rocks (prevent filtration and encourage surface run off), snow melt, steepness of land Human: deforestation (stops interception), urbanisation (more impermeable rocks so more surface run off)

Question 34

Case study: the benefits and threats of living near a river

Answer 34

The Ganges (Bangladesh): Benefits: fertile soil for farming, job opportunities, shrimp farming, trading, economic growth, nice landscapes, minerals from soil, tourism, resources Threats: risk of flooding, Bangladesh is low lying and an LEDC so flooding is terrible, could lose housing, could lose crops, poor communications

Question 35

Human causes of flooding

Answer 35

- Nepal has a land clearance of 1.7% a year leading to more discharge - global warming - urbanisation - deforestation - inadequate drainage facilities - construction of settlements in flood plains - bad design of drainage channels

Question 36

Natural causes of flooding

Answer 36

- snow melt - tectonic activity - low lying - monsoons - impermeable rocks - geology - land type

Question 37

Effects of the 1998 flood

Answer 37

- over 50% of land was flooded - over 1000 people killed - 7 million homes destroyed - shortage of food and water - diseases spread like cholera - rice farms destroyed - half a million cattle lost - cost the country nearly $1 billion - loss of jobs - economic decline

Question 38

Case study: Flood management in Bangladesh

Answer 38

``` Short term: -boats to rescue -fodder for livestock -camps and shelters -repair and rebuild -aid from other countries Long term: -reduce deforestation -build large dams -build flood shelters -build embankments -educate and have flood warning systems ```

Question 39

Case study: Cause of flood in Tewkesbury

Answer 39

- Vulnerable for flooding due to its location with two big rivers (Severn and Avon) - Low pressure system located over Calais slowly moved Northwest bringing warm air. When this air met the cold air to the North, created a storm - no flood defences

Question 40

Case study: Effects of flood in Tewkesbury

Answer 40

- people died - infrastructure destroyed - jobs and businesses effected - economy declined - insurance claims - a lot were made homeless

Question 41

How are the effects of flooding reduced?

Answer 41

- flood proof buildings (stilts) - embankments, dams - forecasting - education from government

Question 42

Hard engineering

Answer 42

Method of river flood management which involves major construction work

Question 43

Soft engineering

Answer 43

Method of river flood management which attempts to work with natural river processes

Question 44

Main case studies

Answer 44

- Opportunities on rivers (Ganges Delta) - Threats to coastlines (Ganges- flooding) - Management on coastlines (Bangladesh)