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Geography iGCSE > 2.2 - Rivers > Flashcards

2.2 - Rivers Flashcards

1
Q

Closed system

A

A system without inputs or outputs

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2
Q

Open system

A

A system with both inputs and outputs

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3
Q

Water stores (4 examples)

A
  • Interception: percipitation that is caught (blocked) by plants
  • Surface storage: water that is held on the surface of the ground
  • Soil moisture: water that is stored in the soil
  • Groundwater: water that is stored undergound
  • Aquifers: permeable rocks such as limestone and sandstone which can hold water
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3
Q

Water stores (definition)

A

Stores are those places where water is held for a period of time.

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4
Q

Water Flows/Transfers

A

The ways in which water is moved around the hydrological cycle

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5
Q

Evaporation

A

The change of water from a liquid to a gas (water vapour) due to the heat from the sun

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6
Q

Condensation

A

The opposite of evaporation; when water vapour turns into liquid
* seen in the formation of clouds

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7
Q

Transpiration

A

The process of water loss through water vapour from plants through their leaves

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8
Q

Evapotranspiration

A

The combined transfer of water vapour from the Earth’s surface and from plants

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9
Q

Percipitation

A

The transfer of water from the atmosphere to the Earth’s surface in the form of hail, sleet, snow or rain

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10
Q

Overland flow

A

Water flowing across the Earth’s surface

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11
Q

Infiltration

A

When the water moves down from the surface into the soil

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12
Q

Percolation

A

The transfer of water down into the rocks and aquifers

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13
Q

Through flow

A

The movement of water through the soil between the groundwater store (water table) and the surface

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14
Q

Groundwater flow

A

The flow of water through rock

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15
Q

Tributaries

A

A smaller river that joins a larger one.

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16
Q

Channel

A

The river course or the deepest part of the river.

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17
Q

Confluence

A

The point at which rivers meet.

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18
Q

Watershed

A

The boundary of a drainage basin. The highland separating one river basin from another. Also called divide.

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19
Q

Drainage Basin

A

The area of land drained by a river and its tributaries. Or called a catchment.

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20
Q

Source

A

Where a river starts, usually in the mountains.

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21
Q

Mouth

A

Where a river ends, at a lake or the sea.

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22
Q

Open system

A

A system which has both inputs and outputs

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23
Q

Drainage density

A

The total length of a channel divided by the total area of the drainge basin
* Drainage basins with lots of tributaries have a high drainage density
* Drainage basins with few tributaries have a low drainage density

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24
Q

River bed

A

The bottom of the river
* made of sand, rocks or mud

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25
Q

River bank

A

The land along the edge of a river

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26
Q

Erosion

A

The gradual wearing down of surfaces over a period of time
* the surface of the river bed and river banks are being destroyed (eroded) by the energy in a river

27
Q

Types of erosion processes in a river

A
  • Abrasion
  • Hydraulic Action
  • Attrition
  • Solution (Corrosion)
28
Q

Hydraulic Action

A

The water forces air to be trapped in cracks in the rocks on the bank of the river. This constant pressure eventually causes the rocks to crack and break apart.

29
Q

Solution (Corrosion)

A

The chemical erosion of the rocks of the riverbank by the slightly acidic water. This occurs in streams running through rocks such as chalk and limestone.

30
Q

Abrasion

A

The erosion of the riverbed and the riverbank by materials being carried by the river.

31
Q

Attrition

A

The rocks and pebbles being carried by the river crash against each other, wearing them down to become smaller, rounded pebbles.

32
Q

Vertical erosion

A

Dominant in the upper course of rivers.
* It increases the depth of the river and valley, as the river erodes downwards

33
Q

Horizontal erosion

A

Dominant in the middle and lower course of rivers.
* It increases the width of the river and valley as it erodes sideways

34
Q

Transportation

A

The river picks up sediment and smaller rocks (depending on the energy it is carrying) and carries them downstream.

35
Q

Types of transportation processes in a river

A
  • Traction
  • Saltation
  • Suspension
  • Solution
36
Q

Traction

A

Occurs when larger rocks and material are rolled along the river bed

37
Q

Saltation

A

When smaller material which can be lifted by the water, bounces along the river bed

38
Q

Suspension

A

Lighter material carried within the flow

39
Q

Solution

A

When materials are dissolved and carried in the river water

40
Q

Deposition

A

When a river does not have enough energy to carry materials it drops them.

41
Q

What might cause a reduce of energy in rivers (4)?

A
  • Reduced discharge due to a lack of precipitation or abstraction upstream
  • Decreased gradient
  • Slower flow on the inside of a river bend or where the river is shallower
  • When the river enters a sea/ocean or lake
42
Q

Bedload

A

The heaviest material is deposited first

43
Q

Alluvium

A

The lighter materials, gravel, sand and silt are known as alluvium and they are carried further downstream

44
Q

Bradshaw model

A
45
Q

Long profile river characteristics (name 3)

A
  • The source is usually in an upland area
  • The upper course of the river includes areas which are steep with uneven surfaces
  • In the middle course the gradient decreases
  • In the lower section the gradient decreases further until it becomes almost flat
46
Q

Cross profile upper course characteristics (name 4)

A
  • Shallow
  • Steep valley sides
  • Narrow
  • Low velocity
  • Large bedload
  • Rough channel bed
  • High levels of friction
  • Vertical erosion
47
Q

Cross profile middle course characteristics (name 4)

A
  • Deeper than upper course channel
  • Gentle valley sides
  • Wider than upper course channel
  • Greater velocity than upper course channel
  • Material in river decreases in size
  • Smoother channel bed
  • Lower levels of friction than upper course channel
  • Lateral erosion
48
Q

Cross profile lower course characteristics (name 4)

A
  • Deeper than middle course channel
  • Flat floodplains
  • Wider than middle course channel
  • Greater velocity than the middle course channel (apart from as the river enters the mouth)
  • Material carried mainly sediment and alluvium
  • Smooth channel bed
  • Lowest friction
  • Deposition is dominant
49
Q

Upper course landforms

A

Waterfalls
Gorges
V-shaped valleys
Interlocking spurs

50
Q

Waterfall and gorge formation

A
  1. A layer of hard rock is on top of soft rock.
  2. Soft rock is easily eroded by undercutting through hydraulic action and abrasion caused by the force of splash back.
  3. A plunge pool at the bottom of the water is formed due to erosion processes.
  4. The overhang of the hard rock collapses without support.
  5. Waterfall retreats as the processes above repeats and a gorge is formed.
51
Q

V-shaped valley formation

A
  1. Vertical erosion in the upper course of the river by processes of erosion causing breakdown of the valley sides – big rocks.
  2. The big rocks move down the valley (steep gradient) and they are gradually transported away by the river.
  3. So river bed continues to be eroded vertically and becomes deeper.
52
Q

Interlocking spurs formation

A
  1. Interlocking spurs occur when the river changes its direction and flows around hard rock.
  2. There is less energy for lateral erosion due to low discharge, between spurs of higher land interlocking spurs are created.
  3. Erosion is concentrated on the outside banks. This creates spurs which change on each side of the river, so they interlock.
53
Q

Flood plain formation

A
  1. In lower course, the river carries large amount of sediments.
  2. In flooding, river overflows the banks, floods and brings sediments to surrounding land.
  3. When the water is displaced slowly or when water retreats slowly, sediments (alluviums – clay and silt) are deposited in layers.
54
Q

Levee formation

A
  1. When a flood occurs, the river bursts its banks.
  2. As the flood overflows the land, it leaves behind the sediments because the velocity drops.
  3. The heaviest materials are deposited at the channel edges, whereas the fine ones further from the edges.
  4. The sediments build up on the river banks and raise above the floodplain.
  5. If more flooding occurs then the levees keep getting higher in layers.
55
Q

Meander and oxbow lake formation

A
  1. River changes direction around hard rock and winds (bends).
  2. It flows faster on outer bends which are eroded laterally with erosion processes undercutting the river cliff.
  3. With continuous erosion, the river cliff on the outer bends collapse, whereas materials are deposited on the inner bends forming slip-off slope.
  4. This causes the river channel to be more winding. So the neck of meander narrows/meander becomes more bended.
  5. Floods would cut through the meander neck, forming new straight river channel.
  6. Former meander is sealed off by deposition as the oxbow lake in moon shape.
56
Q

Delta formation

A
  1. Fan-shaped or triangular shape area of alluvium (deposited sediments) at the river mouth.
  2. At the river mouth the river is slowed as it meets the denser sea water. So much of the load is dropped and it is deposited faster than the tides can remove it out to sea.
  3. The river flow is blocked by deposition so that the river split up into smaller channels known as distributaries.
  4. These distributaries deposit sediment over a wide area, creating new land where there was once sea.
57
Q

What are the two main reasons why flooding occurs?

A
  • If there is a period of heavy, torrential rain leading to high levels of overland flow because the water cannot infiltrate
  • A prolonged period of steady rain which means that the ground becomes saturated leading to high levels of overland flow because the water cannot infiltrate
58
Q

Negative impacts of flooding (name 5)

A
  • Flood waters may increase the spread of water related diseases;
    • The water may act as a breeding ground for the animals that spread disease for example, the mosquito
    • The water may be contaminated by bacteria which can spread diseases such as cholera
  • Deaths and injuries as floodplains are often densely populated due to the fertile soils
  • Bridges and transport routes may be damaged or destroyed by the flood waters
  • Erosion of the river banks leads to the loss of farmland, housing and transport routes
  • Destruction of crops
  • Increased insurance costs
  • Lower house prices
59
Q

Opportunities posed from flooding or at areas with a high risk of flooding (name 4)

A
  • The silt deposited during flooding is often rich in minerals and nutrients, making it ideal for growing crops
  • Rivers are a source of food
  • The floodplains are flat land which makes the construction and building of transport networks easier
  • Water can be used to irrigate farmland
  • Leisure and tourism
  • Generating electricity
  • Transporting goods and people
60
Q

Hydrograph

A

Flood hydrographs are used to predict the reaction of a river discharge to a rainfall event
* shows the changes in river discharge after a storm event

61
Q

Explain the features of a hydrograph:
* Base flow
* Storm flow
* Peak rainfall
* Bankfull discharge
* Peak discharge
* Lag time

A
  • Base flow – The base flow of the river represents the normal day to day discharge of the river and is the consequence of groundwater seeping into the river channel.
  • Storm flow – storm runoff resulting from storm precipitation involving both surface and through flow.
  • Bankfull discharge – the maximum discharge that a particular river channel is capable of carrying without flooding.
  • Peak discharge – the point on a flood hydrograph when river discharge is at its greatest.
  • Peak rainfall – the point on a flood hydrograph when rainfall is at its greatest.
  • Lag time – the period of time between the peak rainfall and peak discharge. The shorter the lag time, the greater the chances of flooding.
61
Q

How does lag time effect the risk of flooding in an area?

A
  • Rivers with a short lag time and steep rising limb have a much greater risk of flooding
    • The water reaches the river rapidly and the river may not have the capacity to cope with the influx of water
  • Rivers with a long lag time and gentle rising limb have a lower flood risk
    • The water reaches the river more slowly causing a gradual increase in discharge
62
Q

Human factors which Increase the Risk of Flooding (4)

A
  • Deforestation: Lack of trees reduces interception and infiltration, increasing overland flow
  • Urbanisation: Impermeable concrete and tarmac increase overland flow - Water flows into the drains reaching the river rapidly
  • Agriculture: Bare soil and ploughing increase overland flow
  • Climate change: Rising global temperatures may increase storm frequency and intensity as it increases the rate of ice and glaciers melting
63
Q

Physical factors which Increase the Risk of Flooding (name 4)

A
  • Relief: Steep slopes reduce infiltration and increase overland flow
  • Rock type: Impermeable rocks reduce percolation and increase overland flow
  • Soil: Frozen, saturated or compacted soil reduces infiltration and increases overland flow - Some soil types such as clay reduce infiltration and increase overland flow
  • Weather: Heavy or prolonged rainfall means that the rate at which water reaches the surface exceeds the infiltration rate leading to increased overland flow
    • After a period of snow rising temperatures can cause rapid melting which increases overland flow
  • Seasonal Variation: In areas affected by monsoon much of the annual rainfall occurs in a few weeks saturating the ground and increasing overland flow - Higher temperatures in spring leads to snow melt in mountainous areas increasing overland flow
    • Flooding in Northern Europe tend to occur in the autumn and winter when rainfall is more frequent
  • Drainage density: Where drainage density is high there are many tributaries taking water to the main channel causing a rapid increase in discharge
  • Vegetation: Where there is little natural vegetation there is reduced interception leading to increased overland flow
64
Q

Hard engineering techniques to reduce the risk or damage of flooding (name 3)

A
  • Dams and reservoirs enable the amount of discharge downstream to be controlled
  • Embankments or levées increase the capacity of the river
  • Straightened channels mean that the river flows more quickly pass vulnerable areas, reducing the risk of flooding
  • Flood relief channels allow some water to flow out of the main channel reducing the discharge
  • Spillways or overflow channels these take excess water away from the main channel
65
Q

Soft engineering techniques to reduce the risk or damage of flooding (name 3)

A
  • River restoration, this supports the river by restoring it back to its original regime - putting meanders back in, stabilising banks and connecting to flood plains
  • Wetland conservation - these areas provide somewhere for excess water to go and slow the flow of the flood water
  • Catchment management plans assess the risk of flooding in an area and outline how this will be managed
  • Flood plain zoning means that only certain land uses are allowed on the flood plain, reducing the risk
  • Afforestation involves the planting of vegetation and trees to increase interception and infiltration

Geography iGCSE (38 decks)

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