Rivers Flashcards
1
Q
How might infrastructure impact surface run off
A
Increases surface run off as it is impermeable, therefore increasing flood risk
2
Q
How might deforestation impact interception
A
Stops stem flow as less water is intercepted
3
Q
What is the mouth of a river
A
The end of a river (usually where the river joins the sea)
4
Q
What is the source of a river
A
The start of a river
5
Q
What is the drainage basin
A
The area of land drained by a river and its tributaries
6
Q
What is a confluence
A
Where a tributary joins a larger river
7
Q
What is the watershed
A
The edge of a river basin
8
Q
What is a tributary
A
A small stream that joins a large river
9
Q
What happens as you move from upper to lower course
A
River channel becomes wider and deeper
10
Q
Upper course characteristics
A
Narrow valley, steep channel
11
Q
Upper course processes
A
River erodes vertically and erosion is dominant
This is because discharge is smaller and the river cuts down in a bid to get to sea level, the rock is also more resistant
12
Q
Upper course landforms
A
Waterfalls
Gorges
V - shaped valley
Interlocking spurs
13
Q
Middle course characteristics
A
Wide valley and shallow channel
14
Q
Middle course processes
A
River erodes laterally
This is because material carried by the river can erode the banks
The river also transports material and deposits some of that in the middle course
15
Q
Middle course landforms
A
Meanders
Oxbow lakes
16
Q
Lower course characteristics
A
Very wide valley and flat channel
17
Q
Lower course processes
A
Deposition is most dominant as the river slows down, losing energy
18
Q
Lower course landforms
A
Levees
Floodplains
Mudflats
Estuary
19
Q
Erosion definition
A
The wearing away of material
20
Q
Hydraulic action
A
Sheer force of water hitting the bed and banks of a river, causing material from the channel to be broken away
Most effective with large volumes of water moving quickly
21
Q
Abrasion
A
River load scraping against the bed or banks of the river, causing other material to be broken away
22
Q
Solution
A
Where the water is slightly acidic and dissolves certain rocks on the river bed and banks, and carries them as the water flows
23
Q
Attrition
A
Rocks carried by the river collide with each other and break into smaller pieces
24
Q
Which processes are erosion processes
A
Hydraulic action
Abrasion
Solution
Attrition
25
Traction
Large particles are rolled along the river bed by the force of the water at times of high discharge
26
Saltation
Small rocks and sand particles are bounces along the river bed by the flow of water
27
Suspension
Fine clay and sand particles are carried along within the water even at low discharges
28
Transportation processes
Traction
Saltation
Suspension
Solution
29
What is the load
Material that is carried by the river
30
Deposition
When some or all of the material being transported by the river is dropped (deposited)
This usually occurs when the velocity of the river slows, reducing the energy of the water
Heaviest material will be dropped first
31
Formation of interlocking spurs (upper course)
Vertical erosion in upper course creates steep sided, V-shaped valleys
The river lacks lateral erosion so they have to wind around hillsides
32
Waterfall and gorge formation (upper course)
There are 2 types of rock: hard and soft
The soft wears away quicker, leaving an overhang of hard rock
This hard rock is unsupported and collapses into the river bed
These rocks become the load, and scrape away the base off the river via abrasion, creating a plunge pool
Overtime, the river retreats and a gorge (steep-sided) is left behind
33
Meander formation (middle course)
The faster flow of water (thalweg) naturally swings towards the outer bed
Water flow has the most energy here due to decreased friction on the outer bend as it is deeper (erosion)
Therefore erosion is on the outside
Deposition is on the inside
34
Oxbow lakes formation (middle course)
Water flows over land, water swings to outside of the bend where there is less friction
As the river erodes the bank, a bend occurs (meander)
On the inside of the bend, flow is slower, so there are deposits of sediment
The neck of the river grows narrower
When the neck of the river breaks through, the river will take the fastest route and go on a straight course
The meander becomes sealed off - this is called an oxbow lake
Eventually it will dry up - this is called a scar
35
What is a levee
A raised bank formed on the banks of a river, in the lower course
36
What is a floodplain
The area around a river that is covered in times of a flood
This is a large, flat area of land formed by deposition and erosion
37
Formation of floodplains and levees
When a river floods it deposits the heaviest load first, these larger particles form the levees
As the water continues to flood further from the river banks, the sands are deposited next, then silts, then light clay
This build up leads to the formation of a flat piece of land (floodplain)
Every time the river floods deposition builds up the floodplain
38
What is an estuary
Where a river meets the sea
The river here is tidal and when the sea retreats the volume of water in the estuary is less reduced
When there is less water, the river deposits silt to form mudflats which are an important habitat for wildlife
39
Flood definition
An overflow of a large amount of water beyond its normal limits
40
Discharge definition
The volume of water which flows through a given time (cumecs)
41
Human factors affecting flood risk (3)
Urbanisation
Agriculture
Deforestation
42
How does urbanisation impact flood risk
Building in areas of 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
43
How does agriculture impact flood risk
In arable farming, soil is left unused and exposed to the elements for periods of time
This can lead to more surface run off
44
How does deforestation impact flood risk
Trees take up water, therefore cutting them down means that areas have less trees to take up water and therefore it is rapidly transferred into river channels
Also less interception
45
Physical factors impacting flood risk (5)
Rock type
Basin size
Soil saturation
Relief
Precipitation (rainfall)
46
How does rock type impact flood risk
Impermeable rocks (clay) don’t allow water to pass through them, therefore a river is more likely to flood
This is because water won’t seep into the rock, resulting in more water flowing over land into the river
47
How does basin size impact flood risk
Larger basins can store more water —> decreased flood risk
48
How does soil saturation impact flood risk
When soil can no longer absorb any more water, it becomes over saturated and causes flow of water over land
49
How does relief impact flood risk
Steep slopes allow for water to be run over the land quicker, leaving little time for water to seep into the soil, therefore more water enters the river
50
How does precipitation impact flood risk
Torrential rainfall can lead to flash floods as river channels cannot obtain the amount of water falling into them
51
Hard engineering strategies
Dams + reservoirs
Channel straightening
Embankments
Flood relief channels
52
What is hard engineering
Man made structures used to control and prevent flooding/erosion
53
How do dams and reservoirs work
Large concrete barriers built across a river to hold back its flow
It 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 monitored and controlled there should be no flooding down stream)
54
Positives and negatives of dams and reservoirs
+attracts tourists
+very effective
-expensive
-displacement of people
-dams trap sediment
-habitats flooded
55
How does channel 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
Usually happens at low lying areas at risk of flooding
56
Positives and negatives of channel straightening
+good in built up areas
+more water held in channel
-dredging required frequently
-increased flood risk downstream
57
How do embankments work
They are raised river banks
Therefore more water is contained in the channel, reducing flood risk
Made by bulldozers moving huge mounds of impermeable soil on to the river banks to build up their height
58
Positives and negatives of embankments
+effective
+holds more water
-expensive
-disrupt habitats
-less attractive
59
How does flood relief work
When another channel is built to deliberately move water away from human settlements during times of high discharge
(Back up channel that frequently floods)
60
Positives and negatives of flood relief
+effective
-shifts risk downstream - only effective where bypass sits
61
Soft engineering strategies
Flood warnings + preparation
Flood plain zoning
Afforestation
River restoration
62
How do flood warnings and preparation work
Flood warning - there is a threat to homes and businesses, people should move items of value and turn off electricity
Flood watch - flooding if low lying land + roads is expected, people should be prepared
Severe flood warning - extreme danger to life and property expected
63
Positives and negatives of flood warnings and preparation
+can reduce property damage
+better precautions for future floods
-climate change - flashier floods - not a permanent fix
64
How does flood plain zoning work
Land uses increased in value as distance from river increases
65
Positives and negatives of flood plain zoning
+less of an impact on people and property
-might already have settlements in flood prone areas
66
How does afforestation work
Planting more trees reduces surface runoff off as there is more interception
Increased precipitation means increased water absorption from roots
This slows down the lag time
67
Positives and negatives of afforestation
+creates habitats
+flood mitigation
+climate regulation
-water consumption
-land use conflicts
-time and resources required
68
How does river restoration work
The process of returning a river to a more natural state
69
Positives and negatives of river restoration
+habitat improvements
+flood mitigation
+reduced erosion
+aesthetically pleasing
-very expensive
-long term funding required to maintain
-land use conflicts
70
Jubilee river flood relief channel facts and figures
Length - 215 miles long
Direction - NE
Cost - £110 million
Organisation funding river - environmental agency
Protects approximately 3200 homes from flood risk in the UK
71
Jubilee river flood relief channel key idea
In flood conditions, the Jubilee River diverts water from the River Thames.
This reduces flood levels in the River Thames running through Maidenhead, Windsor, Eton and Wraysbury
(Windsor and Eton and very expensive areas)
72
Positives of the Jubilee river flood relief channel
-Agency said scheme was working as planned
-Can start to build on areas you couldn’t before as they are now protected
-More woodland, weedbed and wildflower grasslands created
-3000 homes and 500 businesses protected
-Lowers flood risk in Windsor
73
Negatives of the Jubilee river flood relief channel
-Ethically - only some houses protected (richer areas)
-Thames now experiences more discharge
-Small businesses under pressure
-Algae builds up - eutrophication
-Visually unattractive
-People in less affluent areas (old Windsor) believed they were used as a sacrifice to protect affluent areas (Maidenhead)
-Wraysbury residents very angry
