rivers Flashcards
1
Q
what is a drainage basin?
A
an area of land drained by a river and its tributaries
2
Q
what are the 3 sections of a river?
A
upper course
middle course
lower course
3
Q
what is the upper course?
A
has many tributaries
very narrow and v-shaped
low volume of water
sides of river tend to be in a valley
4
Q
what is the middle course?
A
rounder u-shaped valley
deeper than the upper course
water has more energy as there is a higher volume of it
higher erosion rate, this widens the channel
the area around the river channel is low-lying and flat which is the flood plain
5
Q
what is the lower course?
A
very wide very deep
carries the largest volume of water
there are ridges on either side of the river banks called levees.
6
Q
what is the velocity of water?
A
the speed the water travels at is dependant on which course of the river its travelling through
7
Q
what are the types of erosion?
A
vertical erosion
lateral erosion
8
Q
what are the 4 types of erosion?
A
abrasion
attrition
Hydraulic action
solution
9
Q
what is abrasion?
A
where rocks carried by the water scrape and bang against the river and so wear away the channel gradually (sandpaper affect)
10
Q
what is attrition?
A
rocks and pebbles hit against each other, wearing each other down so they become smaller
11
Q
what is hydraulic action?
A
where air is forced into crakes in the rock. high pressure causes crakes to force apart and widen when the wave retreats and air expands
12
Q
what is solution?
A
the river can gradually dissolve chemical compounds in the rock that it flows over
13
Q
what are the transportation processes?
A
14
Q
What does transported material depend on?
A
Velocity Of the water
Size of the particles
15
Q
What is the solution?
A
Chemicals are dissolved in the river water
16
Q
What is suspension?
A
Particals and small rocks that are light enough to float within the water
17
Q
What is saltation?
A
Pebbles and small rocks which are too heavy to be suspended bounces along the river channel
18
Q
What is traction?
A
Large rocks are rolled along the river bed
19
Q
What is deposition?
A
When a river drops eroded material
20
Q
What are the stages of deposition?
A
- Deposition is when a river drops the material its transporting
- It occurs when a river looses velocity and energy
- Particals size affects how far material is transported, an therefore where in a river’s course it’s deposited - smaller particles are transported further and deposited closer to the river’s mouth
21
Q
What are the reason why a river slows down and deposits material?
A
The volume of water falls
The amount of eroded material increases
The water is shallower (e.g. on the side of a bend)
The river reaches its mouth
22
Q
What are the river land forms?
A
Upper course
Middle course
Lower course
23
Q
What happens in the middle course?
A
Erosion is the predominant river process
24
Q
What happens in the middle course?
A
Mixture of erosional and depositional landforms
25
What happens in the lower course?
Deposition is the predominant river process
26
What is the typical landform in the upper course?
Waterfalls
Interlocking spurs
V-shaped valley
27
What are the typical landforms in the middle course?
Meanders
28
What are the typical features in the lower course?
Floodplains
ox bow lakes
29
how are interlocking spurs formed?
1. a low discharge in the upper course means less energy to erode
2. when it meets hard rock it can't cat through it meaning it winds around to form spurs
3. as the process continues the spurs appear to interlock forming interlocking spurs
30
what happens in step 1 of a the formation of a waterfall?
in an area where a river flows over an area of hard rock, the soft rock erodes more quickly.
31
what happens in step 2 of a the formation of a waterfall?
the soft rock erodes away around the heard rock overtime, creating a step
32
what happens in step 3 of a the formation of a waterfall?
the soft rock continues to erode undercutting the hard rock. the hard rock is left suspended in the air as an overhang.
the rotational movement of water quickens erosion, creating s deep plunge pool.
33
what happens in step 4 of a the formation of a waterfall?
due to the force of gravity the unsupported overhang collapses.
the broken up rocks full into the plunge pool, which act as tools for erosion and further deepens the plunge pool.
34
what happens in step 5 of a the formation of a waterfall?
erosion continues to undercut underneath the hard rock, creating an overhang again further upstream
35
what happens in step 6 of a the formation of a waterfall?
the continual process of the overhang collapsing causes the waterfall to retreat upstream over time. the plunge pool continues to deepen and the hard rock continues to be undercut to create an overhang
36
what is a gorge?
gorges form form water falls.
as the waterfall retreats upstream it leaves behind a steep valley carves into the rock with the river running along the base.
37
what are meanders?
these are bends in the shape of the river, often found in the middle course.
the creation of meanders is a gradual process which depends on the velocity of the water
38
what are the stages of meander formation?
1. water travels faster on the outside of the bend which means lateral erosion takes place here. this leaves a river cliff, as material falls into the river and gets transported downstream.
2. on the opposite side the water travels slowly and changes direction sharply and so the water loses energy and deposits sediment
3. hence, erosion wears away a cliff on the outer edge of a bend and deposition create a slip-off slope on the inside of the bend
39
what is the thalweg?
the path of the fastest flow of water
40
how are ox-bow lakes formed?
1. in the beginning, the river has meanders that form depending on the speed of the water.
2. erosion happens when the fastest water hits the sides of the meander, whereas deposition occurs on the insides of the bend, where the water its the slowest
3. gradually, erosion bends the river so that the meanders travel towards each other.
4.the neck of the meander will eventually break (normally due to a flood), creating a straight river and a bend where the water is slow if not stationary
5. the old meander becomes separated from the main river as the material gets deposited at the top, creating the separate ox-bow lake.
41
what are the depositional landforms?
floodplains
levees
Estuaries
42
what is a flood plain?
a flat area of land that floods
43
how is a floodplain formed?
when rivers flood, the water slows down, loses energy and deposits the material its transporting this builds up the floodplain
44
what is a levee?
are natural embankments
45
how are leaves formed?
during a flood , eroded material is dropped on the flood plain but the heaviest materiel is deposited closest to the river channel and over time this deposited material build up creating levees
46
what is an estuary?
are title areas where the river meets the sea
47
Where are estuaries found?
at the river mouth where the land is close to sea level and the river valley is at the widest
48
What is the water like at an estuary?
Tidal, it rises and falls each day
49
What happens when an estuary floods over its banks?
It carries silt and sand onto the valley floor
50
What happens when the tide in an estuary reaches its highest point?
The water moves slowly and has little energy, so it deposits sediment.
51
What is created in the estuary over time when the sediment is deposited?
Mud builds up, creating large mudflats e.g. Severn Estuary, Gloucestershire
52
What is exposed at low tide in an estuary?
the muddy banks
53
What is a river case study that you have learnt?
the river Tees
54
What are the valley features in the upper course of the river Tees?
v-shaped
55
What is the gradient in the upper course of the river Tees?
steep
56
In the upper course of the river Tees, what are the river features/landforms?
interlocking spurs
High-force waterfall (whinstone)
low force gorge
57
What are the processes at work in the upper course of the river Tees?
vertical erosion - hydraulic action
abraison, attirtion, solution
58
What are the valley features in the middle course of the river Tees?
u-shaped
59
What is the gradient in the middle course of the river Tees?
gently sloping
60
What are the river features/landforms in the middle course of the Tees?
meanders (near barn and castle)
61
What are the processes at work in the middle course of the river Tees?
lateral erosion
depostion
62
What are the valley features in the lower course of the river Tees?
flat/wide
63
What is the gradient in the lower course of the river Tees?
flat
64
What are the river features/landforms in the lower course of the Tees?
flood plains
ox-bow lake
65
What are the processes at work in the lower course of the river Tees?
deposition
66
What is a flood management river cast study you have looked at?
Jubilee River
67
What are some general facts about the Jubilee River?
opened in 2012
cost: £110 million
has 5 weirs, large dams, has high discharge, low water levels
11.7km long, 50m wide
designed to look like a natural river
68
What even is the Jubilee River?
a relief channel for the River Thames
runs through Berkshire + Buckinghamshire
flows parallel to the Thames
69
Why was the Jubilee River needed?
Thames floodplain is low lying + prone to flooding
lots of impermeable surfaces, which result in flooding following heavy rainfall
70
Why was the Jubilee River created?
to take the overflow water from the Thames in terms of discharge after heavy rainfall
71
What are the social issues with the Jubilee River?
3000 homes protected
Thames at Old Windsor now suffers high discharge due to the merging of 2 channels upstream
paddleboarders promised navigatable river - 2 weirds mean they have to carry their boards
Taplow weir is too dangerous
72
What are the environmental issues with the Jubilee River?
extensive issues downstream
concrete weirs look ugly
algae collect behind weirs
disrupts natural ecosystems
73
What are the economic issues with the Jubilee River?
most expensive flood relief scheme in the UK (£330 million)
repair of slough weir cost £680,000
maintaining the channel is a huge economic burden
74
What is hard engineering?
man-made structures built to control the flow of rivers and reduce flooding
75
What are some examples of hard engineering?
Dams and reservoirs
channel straightening
embankments
flood relief channels
76
What is a dam and a reservoir?
Dams are barriers built across the rivers, usually in the upper course.
A reservoir (artificial lake) is formed behind the dam.
77
What are the pros of dams and reservoirs?
Reservoirs store water (e.g. after heavy rain), control water flow and prevent floods downstream.
They can also be used to generate hydroelectric power (HEP).
78
What are the cons of dams and reservoirs?
Dams are very expensive to build. Creating a reservoir can flood existing settlements.
Material is deposited in the reservoir, not along the river's course, so farmland downstream can become less fertile.
79
What is channel straightening?
Meanders are removed by building straighter, artificial channels.
80
What are the pros of channel straightening?
Water leaves the area more quickly rather than building up, so flood risk is lower.
81
What are the cons of channel straightening?
Flooding may happen downstream instead.
Faster-moving water may cause more
erosion downstream.
82
What are embankments?
Raised walls are built along river banks.
83
What are the pros of embankments?
The river can hold more water, so floods are less frequent.
84
What are the cons of embankments?
They're quite expensive, and there's a risk of severe flooding if the water rises above the level of the embankments or if they break.
85
What are flood relief channels?
Channels are built to divert water around built-up areas or to divert excess water if the river level gets too high.
86
What are the pros of flood relief channels?
Gates on the channels mean that the release of water can be controlled, reducing flood risk.
87
What are the cons of flood relief channels?
There will be increased discharge where the relief channel rejoins the river (or joins another river), which could cause flooding in that area.
88
What is soft engineering?
Schemes are set up using knowledge of a river and its processes to reduce the effects of flooding.
89
What are examples of soft engineering?
flood warnings and preparation
flood plain zoning
planting trees
river restoration
90
What are flood warnings and preparation?
The Environment Agency issues flood warnings through various media (e.g. TV, radio, internet).
Buildings are modified to minimise flood damage.
Residents can prepare sandbags and flood boards prior to floods.
91
What are the pros of flood warning and preparation?
Warnings give people time to move possessions upstairs, put sandbags in place or evacuate.
This reduces the impact of flooding.
92
What are the cons of flood warning and preparation?
Warnings don't prevent floods.
People may not have access to the warnings.
Modifying buildings is expensive.
Preparation doesn't guarantee safety from a flood and it could give people a false sense of security.
93
What is floodplain zoning?
Restrictions prevent building on parts of a flood plain that are likely to be affected by a flood.
94
What are the pros of floodplain zoning?
Flood risk is reduced - fewer impermeable surfaces are created (e.g. roads).
The impact of flooding is also reduced — there are no buildings to damage.
95
What are the cons of floodplain zoning?
The expansion of an urban area is limited if there aren't any other suitable building sites.
It can't help in areas with existing buildings.
96
What is planting trees?
Planting trees in the river valley increases the interception of rainwater (and lag time).
97
What are the pros of planting trees?
Discharge and flood risk decrease.
Vegetation reduces soil erosion in the valley and provides habitats for wildlife.
98
What are the cons of planting trees?
Less land is available for farming.
99
What is river restoration?
Making the river more natural, e.g. by removing man-made levees, so the flood plain can flood naturally.
100
What are the pros of river restoration?
Discharge is reduced, so there's less risk of flooding downstream.
Little maintenance is needed, and there are better habitats for wildlife.
101
What are the cons of river restoration?
Local flood risk can increase, especially if nothing is done to prevent major flooding.
