3.1.3.3- River Landscapes in the UK Flashcards
1
Q
What is a drainage basin?
A
The land that is drained by a river system.
2
Q
What is the source of the river?
A
The beginning/start of a river
3
Q
What is a confluence?
A
The point at which two rivers/streams join.
4
Q
What is the mouth?
A
The point where the river comes to an end, usually when entering a sea.
5
Q
What is a tributary?
A
A stream or smaller river which joins a larger stream/river.
6
Q
What is the watershed?
A
The edge of highland surrounding a drainage basin which marks the boundary between two drainage basins
7
Q
What is the long profile of a river?
A
The long profile of a river shows the changes in the river gradient from the source to the mouth
8
Q
What are some characteristics that most long profiles share?
A
Most long profiles have a concave shape with similar characteristics:
1. The source is usually in an upland area
2. The upper course of the river includes areas which are steep with uneven surfaces
3. In the middle course the gradient decreases
4. In the lower section the gradient decreases further until it becomes almost flat
9
Q
What is the cross profile of a river?
A
The cross profiles of a river are cross-sections from one bank to another
10
Q
What are some key characteristics of the upper course?
A
Shallow
Steep valley sides
Narrow
Low velocity
Large bedload
Rough channel bed
High levels of friction
Vertical erosion
11
Q
What are some key characteristics of the middle course?
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
12
Q
What are some key characteristics of the lower course?
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
13
Q
Where is the River Severn located?
A
The River Severn is located in the United Kingdom, in Wales and England.
14
Q
How long is the River Severn?
A
It is 354 km long (the longest river in the UK).
15
Q
Describe the route the River Severn takes from source to mouth.
A
Its source is in the Cambrian Mountains of mid Wales. It then flows through Shropshire, Worcestershire and Gloucestershire before entering the Bristol Channel.
16
Q
What is the waterfall in the River Severn?
A
Waterfall- Severn Break-it’s-Neck. Found within the first few miles from the source of the river.
17
Q
Where are the meanders found in the River Severn?
A
Many meanders are found around Caersws, halfway between Aberystwyth and Shrewsbury, because the river is now flowing across low land. The Severn begins to wander from side to side across the valley floor.
18
Q
Where is the estuary in the River Severn?
A
The tidal part of the river where it meets the Bristol Channel. It is at the mouth of three major UK rivers- the Severn, Wye and Avon. The rivers carry a lot of sediment as they travel from the source to the mouth. Much of this sediment is dropped at the mouth where the rivers flow more slowly.
19
Q
How have people altered river processes at work in the River Severn?
A
Large areas of the river’s banks within urban areas have been reinforced with concrete and brickwork preventing the natural processes of erosion and deposition therefore halting the formation and migration of meanders
Artificial levees to prevent flooding have also stopped the deposition of sediments on the floodplains in areas affected that would create natural levees and fertilise soils
Dams have increased deposition behind them and reduced to flow of sediment down- stream
20
Q
What is erosion?
A
The wearing away of surfaces?
21
Q
What are the four main types of erosion?
A
- Hydraulic action
- Abrasion
- Attrition
- Corrosion
22
Q
What is hydraulic action?
A
The force of the river against the banks can cause air to be trapped in cracks and crevices. The pressure weakens the banks and gradually wears it away
23
Q
What is abrasion?
A
Rocks carried by the river wear down the river bed and banks.
24
Q
What is attrition?
A
Rocks carried by the river smash together and break into smaller, smoother and rounder particles
25
What is corrosion?
a chemical erosion process where water, especially seawater, dissolves rock minerals, causing them to break down and be carried away in solution.
26
Where is vertical erosion dominant?
Vertical erosion is dominant in the upper course of rivers. It increases the depth of the river and valley, as the river erodes downwards
27
Where is lateral erosion dominant?
Lateral erosion is dominant in the middle and lower course of rivers. It increases the width of the river and valley as it erodes sideways
28
What are the four processes of transporation in rivers?
1. Traction
2. Saltation
3. Suspension
4. Solution
29
What is traction?
The rolling of pebbles and boulders along the river bed
30
What is saltation?
Particles bouncing along the river bed
31
What is suspension?
Fine solid material held in the water while the water is moving
32
What is solution?
Soluble particles are dissolved in the river.
33
What are two movement processes in the valley?
1. Mass movement
2. Weathering
34
What is mass movement?
refers to the downslope movement of soil, rock, and debris under the influence of gravity
35
What is weathering?
wearing down/breaking of rocks by natural processes
36
What is deposition?
Deposition is when a river does not have enough energy to carry its material and it drops it
37
What are some causes of deposition?
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 as the gradient is more gentle and the river flow is affected by tides
38
How does deposition occur?
1. The heaviest material is deposited first, this is known as the bedload
2. Larger rocks are only moved short distances before being deposited
This happens at times of high discharge and in the upper section of the river
3. The lighter materials, gravel, sand and silt are known as alluvium and they are carried further downstream
4. The dissolved materials are carried out to sea
39
How are waterfalls and gorges formed? (erosional landform)
1. River flows over bands of hard and soft rock
2. The soft rock erodes faster (by hydraulic action and abrasion), leaving an overhang
3. A plunge pool formed at the base as erosion deepens the soft rock
4. The hard rock becomes unsupported and collapses into the plunge pool
5. This collapsed rock increases abrasion in the plunge pool, making it deeper
6. This process repeats and the waterfall retreats upstream
7. This leaves behind a steep sided gorge
40
How are V-shaped valleys formed (erosional landform)?
1. Vertical erosion by the river cuts down into the river bed
2. This deepens the channel, forming a narrow valley
3. Weathering and mass movement causes the valley sides to collapse
4. The collapsed material is transported by the river
5. Over time, this creates a steep sided, narrow valley?
41
How are interlocking spurs formed (erosional landform)?
1. Near the source, the river lacks energy to erode laterally
2. The river instead flows around more resistant rock outcrops on the valley sides
3. This creates spurs that project into the valley
4. The river winds around them, forming interlocking spurs
42
How are meanders formed (erosion and deposition landform)?
1. In lowland areas (the middle and lower course of a river), the gradient is gentle, and lateral erosion (sideways erosion) becomes more dominant than vertical erosion.
2. The thalweg (line of fastest flow) is directed towards the outside bend of the river due to centrifugal force.
This creates high velocity on the outer bank and low velocity on the inner bank.
3. On the outer bend, hydraulic action (water forcing air into cracks) and abrasion (load scraping the riverbed and banks) erode the riverbank.
This forms an undercut bank known as a river cliff.
4. On the inner bend, where flow is slower, deposition occurs as the river loses energy.
This forms a gentle slip-off slope, built up from deposited alluvium.
5. Continuous erosion and deposition cause the meander to migrate laterally (sideways) across the valley floor, enlarging the meander and shaping the floodplain.
43
How are oxbow lakes formed (erosion and deposition landform)?
1. As erosion continues on the outside bends, the meander neck (the narrow strip of land between two bends) becomes increasingly narrow due to abrasion and hydraulic action.
2. During a flood, the river’s energy increases.
The river may cut through the neck, taking a shorter, straighter route as it overflows and bypasses the meander loop.
3. The river establishes a new channel, abandoning the old meander loop.
The thalweg now bypasses the loop entirely.
4. Over time, deposition occurs at the entrance and exit of the old meander loop, sealing it off from the main channel.
5. The cut-off meander loop becomes a crescent-shaped water body called an oxbow lake.
Eventually, this may become a marsh or dry up over time due to evaporation and infilling with silt.
44
How are floodplains formed (depositional landform)?
1. A floodplain is a flat, wide expanse of land found on either side of the river, especially in the middle and lower courses, where the river flows through low-lying land.
2. As the river meanders across the valley, lateral erosion on the outer bends and deposition on the inner bends cause the meanders to migrate sideways.
This widens the valley floor and helps form a flat floodplain.
3. During periods of high discharge, the river may overflow its banks and flood the surrounding land.
As water spreads out over the floodplain, it comes into contact with more of the land surface, causing friction to increase and velocity to decrease.
4. The loss of energy causes the river to deposit its load.
Over time, repeated flooding results in layers of fine sediment (alluvium) being deposited across the floodplain, gradually building it up and making it more fertile.
45
How are levees formed (depositional landform)?
1. When the river floods, it carries a large suspended load of sediment. As the water spills over the banks, its velocity quickly decreases due to increased friction with the land.
2. The heaviest material (e.g. gravel and coarse sand) is deposited first, closest to the river channel, while finer particles are carried further onto the floodplain.
3. Repeated flooding and deposition build up ridges of sediment along the riverbanks. These are called levees—natural raised embankments that run parallel to the river.
4. With each flood, the levees become larger and more pronounced, helping to contain the river and reduce the frequency of small floods. However, they can eventually be breached during extreme flood events.
46
How are estuaries formed (depositional landform)?
1. An estuary is the tidal mouth of a river, where freshwater from the river meets saltwater from the sea. Estuaries are typically found in the lower course of a river.
2. Estuaries are dynamic environments shaped by the interaction between fluvial (river) processes and marine (tidal) processes.
As the incoming tide brings in saltwater and marine sediment, it meets the freshwater and river-borne sediment flowing downstream.
3. When the freshwater and saltwater mix, the river’s velocity suddenly decreases due to the opposing flow of the tide.
This causes deposition of the river’s suspended sediment.
4. The deposited sediment builds up in layers, especially during low tide when water levels drop.
These sediment layers form mudflats, which are flat, muddy areas that can be exposed at low tide and submerged at high tide.
5. Over time, vegetation such as salt-tolerant plants (e.g. eelgrass and cordgrass) begins to colonise the mudflats.
6. The roots of these plants help trap more sediment, which leads to the gradual vertical build-up of the land.
These vegetated areas become salt marshes—important coastal ecosystems that provide habitats and protect against coastal erosion.
47
When does flooding occur?
Flooding occurs when the capacity of the river channel is exceeded and the water flows over the banks and onto the surrounding area.
Flooding is usually the result of heavy or prolonged rainfall.
48
What is the lag time and how does this impact the risk of flooding?
The key factor is the time taken for the precipitation to reach the river from where it falls: the lag time.
The shorter the lag time, the higher the risk of flooding because the discharge of the river increases faster.
The lag time depends on some human and physical factors. These lead to increased overland flow which shortens the lag time
49
What is precipitation?
Rain,hail,sleet,snow
50
What does impermeable mean?
A surface that does not allow water to pass through it
51
What does saturation mean?
When all the spaces and cracks in soil, rock or sand are filled with water.
52
What does interception mean?
The process by which precipiation is prevented from reaching the ground by plants or other features.
53
What does surface runoff mean?
Water that flows over the surface of the land.
54
What is evapotranspiration?
Loss of water from the soil both by evaporation from the soil surface and by transpiration from the leaves of the plants growing on it.
55
What is infiltration?
The process by which water moves through the Earth’s surface and into the soil
56
What is percolation?
The downward movement of water within the rock under the soil surface.
57
How does deforestation impact flood risk?
Lack of trees reduces interception and infiltration, increasing overland flow. The lack of roots after deforestation means that there is increased rates of erosion, because roots bind the soils. Eroded sediment can block river channels.
58
How does urbanisation impact flood risk?
Impermeable concrete and tarmac increase overland flow
Water flows into the drains reaching the river rapidly
59
How does agriculture impact flood risk?
Bare soil and ploughing increase overland flow, especially where ploughing is downslope
Overgrazing can lead to less vegetation and can also compact the soil, increasing run off, as infiltration will decrease. This means there is a greater discharge.
60
How does climate change impact flood risk?
Rising global temperatures may increase storm frequency and intensity
61
How does relief impact flood risk?
Steep slopes reduce infiltration and increase overland flow
62
How does rock type impact flood risk?
Impermeable rocks reduce percolation and increase overland flow
63
How does soil impact flood risk?
Frozen, saturated or compacted soil reduces infiltration and increases overland flow
Some soil types such as clay reduce infiltration and increase overland flow
64
How does weather impact flood risk?
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
65
How do seasonal variations impact flood risk?
Flooding in Northern Europe tend to occur in the autumn and winter when rainfall is more frequent
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
66
How does drainage density impact flood risk?
Where drainage density is high there are many tributaries taking water to the main channel causing a rapid increase in discharge
67
How does vegetation impact flood risk?
Where there is little natural vegetation there is reduced interception leading to increased overland flow
68
What is a hydrograph?
A hydrograph is a graph showing the river discharge at a certain point. It shows the response of a river to a rainfall event, plotting rainfall and river discharge (volume of water flowing per second, measured in cumecs (cubic metres per second).
69
How do rivers with a short lag time respond to flood events?
Rivers with a short lag time respond quickly ro rainfall events and are therefore more prone to flooding. (opposite for long lag time).
70
Peak discharge?
The highest discharge in the period of time that you are looking at.
71
Lag time?
Delay between peak rainfall and peak discharge.
72
Raising limb?
Increase in river discharge as rainwater flows into the river.
73
Falling limb?
Decrease in river discharge as the river returns to its normal level.
74
What are the differences between a flashy hydrograph and a low, flat hydrograph?
Basin size
Flashy hydrograph: Small basins often lead to rapid water transfer.
Low, flat hydrograph: Large basins result in a relatively slow water transfer.
Drainage density
Flashy hydrograph: A high density speeds up water transfer.
Low, flat hydrograph: A low density leads to a slower transfer.
Rock type
Flashy hydrograph: Impermeable rocks encourage rapid overland flow.
Low, flat hydrograph: Permeable rocks encourage a slow transfer by groundwater flow.
Land use
Flashy hydrograph: Urbanisation encourages rapid water transfer.
Low, flat hydrograph: Forests slow down water transfer because of interception.
Relief
Flashy hydrograph: Steep slopes lead to rapid water transfer.
Low, flat hydrograph: Gentle slopes slow down water transfer.
Soil moisture
Flashy hydrograph: Saturated soil results in rapid overland flow.
Low, flat hydrograph: Dry soil soaks up water and slows down its transfer.
Rainfall intensity
Flashy hydrograph: Heavy rain may exceed the infiltration capacity of vegetation, leading to rapid overland flow.
Low, flat hydrograph: Light rain will transfer slowly and most will soak into the soil.
75
What is hard engineering?
Hard engineering involves building structures or changing the river channel
Four examples of this are:
1. Dams and reservoirs
2. Embankments/ Levees
3. Straightening channels
4. Flood relief channels
76
How do dams and reservoirs work?
Controls the river flow by blocking the river and letting water in a controlled way. This creates a reservoir behind the dam
77
What are some advantages to dams and reservoirs?
Multi-purpose can be used for energy production (HEP) and water storage as well as flood control
Provides opportunities for recreation: Water sports, fishing
78
What are some disadvantages to dams and reservoirs?
Expensive
Loss of farmland and homes due to reservoir creation
Displacement of people
Effects on ecosystems: can affect fish breeding
Reservoir silts up over time
79
How do embankments and levees work?
Artificially raise the banks of the river, increasing channel capacity
80
What are some advantages to embankments and levees?
Increased river capacity means it is less likely to flood
New river bank habitats may be created
81
What are some disadvantages to embankments and levees?
Expensive
Visually unattractive particularly if made from concrete
May fail and lead to more serious flooding
82
How does straightening channels work?
Straightening the river channel by removing meanders
83
What are some advantages to straightening channels?
Speeds up the movement of water over a short distance
Allows easy navigation for boats
84
What are some disadvantages to straightening channels?
May increase flood risk downstream as the discharge reaches those areas more quickly
Expensive
Affects river ecosystems due to changes in velocity
85
How do flood relief channels work?
Channels built to allow excess water to flow around high value areas
86
What are some advantages to flood relief channels?
Effective in reducing the flood risk in high value areas
New habitats may be created
Insurance costs may be reduced for people living nearby
87
What are some disadvantages to flood relief channels?
Expensive
Regular maintenance is needed
Disruption to existing habitats
Can be visually unattractive
88
What is soft engineering?
Soft engineering works with natural processes of the river and surrounding environment.
Four examples of this are:
1. River restoration
2. Flood plain zoning
3. Afforestation
4. Flood warnings
89
How does river restoration work?
Restores the river to its natural state with meanders and wetland areas
90
What are some advantages to river restoration?
Increases the number of habitats
Restores wetland areas
Slows down water flow reducing flooding downstream
91
What are some disadvantages to river restoration?
Expensive to construct the new channels
Some areas will flood
92
How does flood-plain zoning work?
Restricts land use in areas that are at high risk of flooding and ensures high value buildings are not in flood prone areas
93
What are some advantages to flood-plain zoning?
Low cost
Conserves habitats on floodplains and wetlands
94
What are some disadvantages to flood-plain zoning?
Restricts areas where houses can be built and may impact on economic development
Can only happen in places where development has not already happened
95
How does afforestation work?
Planting of trees to increase interception and infiltration. Trees also use up large quantities of water
96
What are some advantages to afforestation?
Inexpensive
Absorbs and stores CO2
Slows down water transfer, increasing lag time
97
What are some disadvantages to afforestation?
Can increase acidity in the soil
Loss of farmland
98
How do flood warnings work?
Monitoring of rivers to provide people with warnings when flooding may occur
99
What are some advantages to flood warnings?
Helps people to prepare and evacuate if needed
Less expensive than hard engineering
100
What are some disadvantages to flood warnings?
Expensive to set up monitoring equipment
People may not take warnings seriously
101
Where is Banbury located?
Banbury is located in Oxfordshire, England, and is situated on the banks of the river Cherwell (tributary of the River Thames). Banbury is approximately 64 miles northwest of London and 50 km north of Oxford.
102
Why was flood management required in Banbury?
1998 flood- led to the closure of the railway station and caused £12.5 million in damage
More than 150 homes/business were affected
Further flooding of the town in 2007- river burst its banks after heavy rain
103
What is the flood management strategy in Banbury?
Happened in 2012
Flood storage reservoir north of the town built- at an investemnt of 18.5 million pounds
3 km long x 4.5m high embankments built parallel to M40, to form 3 million cubic meters storage basin
Purpose of the reservoir is to regulate the flow of surplus rainwater into the river, using engineered outlets to discharge the water slowly
When heavy rainfall occurs, surplus water accumulates in storage reservoir
Water then gradually released into the river Cherwell over the following days
104
What were some key features of the Banbury management scheme?
Raising A361
Consturcting floodwall around motorsport company Prodrive
Constructing new pumping stations to transfer water
Controlling the flow of the River Cherwell through the Hardwick and Huscote flow control structures
Biodiversity Action Plan (BAP) habitat with ponds, trees and hedgerows
Constructing 4.5 m embankments using soil taken from the borrow area, which is now a small reservoir used for storing water
105
Social issues from Banbury?
The A361 is no longer affected by flooding, reducing transport disruption for people
The new green areas and footpaths have improved the quality of life for local people
Reduced anxiety in local communities as the risk of flooding has been reduced
106
Economic issues from Banbury?
Cost of the scheme was £18.5 million
The benefits are estimated at over £100 million
441 houses and 73 commercial properties are protected from flooding
Property values have increased as they are no longer at risk of flooding
107
Environmental issues from Banbury?
Around 100,000 tonnes of Earth were required to make the embankment, resulting in some habitat destruction
Biodiversity Action Plan (BAP) has resulted in planting trees, hedgerows and creating new ponds
BAP has created new ponds, trees and habitats
Part of the floodplain will be left to flood if river levels get too high
The reservoir provides a temporary habitat for birds
The concrete apertures are unnatural in the landscape
