rivers Flashcards
1
Q
the hydrological cycle in a drainage basin:
A
precipitation
|
interception ——> transpiration
|
stem flow
|
surface storage
|
infiltration
|
soil moisture ——> through flow
|
percolation
|
groundwater store
|
ground water flow
surface runoff ——> river carrying water to a lake or sea
|
evaporation
2
Q
what does it mean when:
on a global scale, the hydrological cycle is a closed system
A
there are no inputs or outputs - nothing can enter the system or leave the system
3
Q
what does it mean when:
on a local scales, within a drainage basin, the hydrological cycle is an open system
A
there are inputs (e.g. precipitation)
4
Q
water table meaning
A
current upper level of saturate rock/soil where no more water can be absorbed
5
Q
groundwater flow meaning
A
water flowing through the rock layer parallel to the surface
6
Q
through flow meaning
A
water flowing through the soil layer parallel to the surface
7
Q
surface runoff meaning
A
water flowing on top of the ground
8
Q
evaporation meaning
A
water lost from ground/vegetation surface
9
Q
transpiration meaning
A
water lost through pores in vegetation
10
Q
ground water meaning
A
water stored in rock
11
Q
percolation meaning
A
water seeping deeper through rock
12
Q
soil moisture meaning
A
water help in the soil layer parallel
13
Q
infiltration meaning
A
water sinking into the soil/rock form the ground surface
14
Q
surface storage meaning
A
water held on the ground surface .e.g. puddles
15
Q
interception meaning
A
water being prevented form reaching the surface/ground by vegetation or trees
16
Q
precipitation meaning
A
any source of moisture reaching the ground .e.g rain, snow, frost
17
Q
how might human activity impact the hydrological cycle in drainage basin
A
- deforestation would impact interception
-> less trees means water isn’t intercepted - deforestation would impact surface runoff
-> increases speed as less precipitation is intercepted
18
Q
what is the source
A
the start of the river
19
Q
what is the drainage basin
A
the area of land drained by a river and its tributaries
20
Q
what is a confluence
A
where a tributary joins a larger river
21
Q
what is the mouth
A
the end of a river (usually where the river meets the sea)
22
Q
what is the water shed
A
the edge of the river basin
23
Q
what is a tributary
A
a small stream that joins a larger river
24
Q
how many ‘courses’ are there in a river
A
3 - upper, middle, lower
25
how does the long profile of a river change from source to mouth
the gradient decreases from source to mouth
upper - steep
middle - shallow
lower - fairly flat
26
what is the river valley like in the upper course
steep
27
what is the river valley like in the middle course
shallow
28
what is the river valley like in the lower course
flat
29
what is the river channel like in the upper course
narrow
30
what is the river valley like in the middle course
wider
31
what is the river channel like in the lower course
wide
32
what do we mean by ‘fluvial’
water
33
what do we mean by ‘processes’
things that a river does
34
examples of fluvial processes
erosion, transportation, deposition
35
erosion definition
wearing away of material
36
in the upper course of a river what process appears to be dominant
erosion
37
why does the river tend to erode vertically in the upper course
discharge is smaller and the river cuts down in a bid to get to sea level
rock is also resistant
38
why does a river tend to erode laterally in the middle course
material carried by the river can erode the banks
39
what tends to be the dominant process in the lower course of a river and why
deposition because the river slows down and uses energy
40
hydraulic action:
- occurs when the force of the river compresses air trapped in cracks in the banks
- the increased pressure weakens and gradually wears away the banks
41
abrasion:
- occurs when rocks carried by the river scrape and rub along the river bed and banks, wearing them down
42
solution:
- occurs where water is slightly acidic
- dissolves certain types of rock on the river bed and banks
43
attrition:
- occurs as rocks carried by the river collide with each other and break into smaller pieces
44
what is the ‘rivers load’
once material has been eroded by the river, it is often carried along in the river itself
- the materials that are carried by the river are known as the RIVERS LOAD
this load is different sizes and shapes and materials
45
what is the ‘rivers discharge’
amount of water in a river at any given time
46
what is traction
large particles (boulders and rocks) are rolled along the river bed by the force of the water at times of high discharge
47
what is saltation
small rocks and sand particles are bounced along the river bed by the flow of water
48
what is suspension
fine flat and sand particles are carried along (suspended in) within the water even at low discharges
49
what is solution
some minerals dissolved in water such as calcium carbonate. this require very little energy
50
deposition:
- when some or all of the material being transported by river is dropped (deposited)
- this usually occurs when the velocity of the water slows, thus decreasing the energy of the water
- the heaviest material, that takes the most energy to carry will be dropped first
- deposition will happen when a river bursts its banks at a floodplain, or when the river reaches the sea to from a delta
- when a river floods friction with the land slows the water down
- river meander - as it swings around the bend it loses speed on the inside of the bend
- river mouth - slows down as it hits the large body of water
51
characteristics of the river channel and river valley in the upper course of the River severn
valley is steep
channel is narrow
52
characteristics of the river channel and river valley in the middle course of the river severn
valley is wider and less steep
channel is wider and deeper
53
characteristics of river channel and river valley in lower course of river severn
valley is flat and wide
channel is deep and wide
54
landforms in the upper course of the river severn
waterfalls
v-shaped valleys
interlocking spurs
55
landforms in the middle course of the river severn
meanders
oxbow lakes
56
landforms in the lower course of the river severn
leeves
floodplain
estuary
mudflats
57
processes/size of material in the upper course of the river severn
mainly erosion
load is large and angular
58
processes/size of material in middle course of river severn
erosion and deposition
load is slightly smaller and rounded
59
processes/size of material in lower course of river severn
transportation and deposition
load is small and round
60
what do we mean by ‘landforms’
a recognisable, naturally formed feature on the earth’s surface
61
interlocking spurs:
- hillsides which interlock with each other as the river winds around them
- vertical erosion in the upper course creates steep sided, v-shaped valleys
- rivers lack lateral erosion so they have to wind around hillsides
62
formation of a waterfall:
1) water runs over alternating bands of hard rock on the top and soft rock beneath it
2) erosion will start to break down rocks through the processes of hydraulic action, abrasion and solution
3) hydraulic action wears away the soft rock as water runs over it. This is because it is less resistant than the hard rock above it
4) overtime the soft rock starts to undercut the hard rock
5) the hard rock left unsupported and as a result of this and weight it collapses into the river bed
6) rocks that have fallen are either transported down the river or scrape away at the base of the river bed through the processes of abrasion. this coupled with continuous friction of water, a dent in the river bed starts to form - this is known as a plunge pool
7) the erosional processes repeat and overtime the waterfall retreats backwards/upstream
8) once a waterfall retreats, a steep sided gorge is left behind
63
where are the areas of deposition and erosion on a meander and why
deposition - inside bend
erosion - outside bend
because fastest flow of water tends to be on outside bend
64
how do meanders and ox bow lakes form
1) water flows over land, water swings to the outside of the river where there is less friction
2) as the river erodes the river bank, a bend starts to occur, this is known as a meander
3) on the inside of the bend, the flow is slower so we get deposits of sediment
4) the neck of the river grows narrower
5) when the neck of the river breaks through, the river will take the shortest route and take on a straight course
6) the look becomes sealed off altogether as a result of deposition - this is known as an oxbow lake
65
what is a levee
a raised bank formed on the banks of a river, in the lower course
66
how is a levee formed
1) before flood - water is held within the channel
2) during flood - water flows over the banks and deposits silts as the water hasn’t got enough energy to carry the materials
3) the levee gradually gets higher after successive floods
67
what is a floodplain
the area around a river that is covered in times of flood. this is a large, flat area of land that is formed by erosion and deposition
68
how is a floodplain formed
- when a river floods, it deposits the heavier particles first -> forms the levees
- as the water continues to flood further away from the river banks, the sands are deposited next, then the silts and finally the lightest clays
- this buildup of sand, silts and clay leads to the formation of a flat piece of land (floodplain) either side of the river - just after the levees
- every time the river floods, deposition builds up the floodplain
69
what is an estuary
where the river meets the sea
70
what factors increase the risk of flooding
- climate change
- historical flooding
- deforestation
- impermeable rocks or road (concrete)
- heavy rainfall
- urbanisation
- flat land
71
flood definition
flooding occurs when the amount of water in a river exceeds the capacity of the channel causing it to burst its banks onto land around it
72
discharge definition
the volume of water flowing through a river channel; measured at any given point in cubic metres per second (CUMECS)
73
causes of flooding
- urbanisation
- agriculture
- deforestation
- rock type
- basin size
- soil saturation
- relief
- precipitation
74
causes of flooding:
urbanisation definition
building in areas at risk of flooding. areas are made from impermeable rock (tarmac) which means water runs over the roads into drains and then into the river channel causing
75
causes of flooding:
agriculture definition
in arable farming, soil is left unused and exposed to the elements for periods of time. this can lead to more surface runoff
76
causes of flooding:
deforestation definition
trees take up water, therefore if we cut down trees, areas will have less trees to uptake water. therefore it is rapidly transferred into the river channels
77
causes of flooding:
rock type definition
impermeable rocks (eg. clay) do not allow water to pass through them. therefore a river is more likely to flood. this is because water will not seep into the rock.
78
causes of flooding:
basin size definition
when a river basin is large it is able to store more water, however if it is small it has an increased risk of flooding as it cannot carry as much so will overflow
79
causes of flooding:
soil saturation definition
when soil can no longer absorb any more water it becomes over saturated and causes flow of water over land
80
causes of flooding:
relief definition
steep slopes allow for water to run over the land quickly, leaving little time for water to seep into the soil. therefore more water enters the river channels
81
causes of flooding:
precipitation definition
torrential rainstorms can lead to sudden flash floods as river channels cannot contain the volume of water falling into them
82
what is the key factor that leads to flooding
precipitation and how intense / how frequent
83
how might human factors worsen flood risk
due to urbanisation, impermeable flat surfaces prevent rainfall being absorbed, meaning surfaces flood faster. increase surface runoff
84
hard engineering strategies
- reservoirs
- afforestation
- dredging
- land-use zoning
- controlled flooding
- river bank conservation -> tree planting
- channel straightening
- embankment
85
how do dams work
- large concrete barrier built across a river to hold back its flow
- causes the valley behind the dam to flood, creating an artificial lake called a reservoir
- this controls the amount of water downstream
- water is released in a controlled manner through gates in the dam
- if water releases are carefully controlled, there should be no flooding downstream
86
how does channels straightening work
- when a meandering section of a river is engineered to create a widened, straightened and deepened course
- by doing this it can carry more water and reduce flood risk
- this usually happens on low-lying areas that are highly at risk of flooding
87
how does embankments work
- embankments are raised river banks
- by raising these banks, more water is contained in the channel
- this reduces the flood risk
- an embankment is made by bulldozers moving huge mounds of impermeable soil on to the river banks to build up their height
- some embankments are lined with concrete
88
how does flood relief work
- flood relief is when another channel is built to deliberately move water away from human settlements during times of high discharge
- it is essentially a back-up channel for a river that frequently floods
89
flood water description
flooding of low-lying land and roads is expected. people should be prepared and watch river levels
90
flood warning description
there is a threat to homes and businesses. people should move items of value to upper floods and to turn off electricity and water
91
severe flood warning description
extreme danger to life and property is expected. people should stay in the upper floors and turn off electricity and water. people are also informed to leave property
92
soft engineering strategies for flooding
- flood warnings and preparations
- flood plain zoning
- planting trees
- river restoration
93
what is the river management case study
Jubilee river flood-relief channel
94
cost of the jubilee river
£110 million
95
length of the jubilee river
11.7km
96
cost of repairing the channel of the Jubilee river after an episode of flooding
£680,000
97
organisation funding the Jubilee river
EA (environmental agency)
98
year of completion of Jubilee river
2002
99
width of jubilee river
50m
100
year of worst flooding in Thames since 1947
2014
101
how many homes does the flood relief channel in the Jubilee river protect
3200
102
flood relief channel in Jubilee River:
the Jubilee river acts as a flood relief channel for the river Thames, allowing water levels to be controlled and diverted from the Thames during times of high flow
103
Jubilee river:
socioeconomic negatives:
- small businesses and shops are under pressure as they cannot open when premises are flooded and insurance costs are incredibly high. business insurance costs for Wraysbury alone was £500 million in 2014. this causes future insurance premiums to increase too
- paddle boaters had been promised a navigable river. however on two of the fiver weirs they have to carry boats over with them and Taplow Weir is too dangerous to cross
104
Jubilee river:
environmental negatives:
- ethics - some people are protected but not others. 3000 properties in affluent Eton and Windsor are protected, but less wealthy settlements in Wraysbury and Old Windsor are not
- the Thames now experiences a much higher discharge due to the merging of the two channels upstream. this problem came to light in 2014 when the river experienced serious flooding
- in 2014, extensive flooding meant the built environment suffered from flooded roads, buildings, fields and habitats
- the natural ecosystem is affected as algae collects and builds behind the weirs where the flow of the river is slowed or stopped
