P1 River Landscapes Flashcards
How does the long profile of the river change from source to mouth?
The gradient decreases
What landforms are often in the upper coarse of a river?
Interlocking spurs, v shaped valley
What landforms are often in the middle coarse of a river?
Meanders, oxbow lakes
What landforms are often in the lower coarse of a river?
Levees, floodplain,estuaries
What is erosion and how does it work differently in the different courses of the river?
Erosion : the process of breaking down and removing sediment/washing away material
Upper coarse :vertical as the river is flowing faster (bed erosion)
Middle: Lateral as gradient is less steep (bank erosion)
Describe the process of hydraulic action
.river banks have cracks and crevices
.the flow of the river forces air inside cracks
.air inside the cracks is compressed and it expands
.this puts pressure on the river bed causing the cracks to widen and make the bank more unstable
.parts of the bank break away
(Active at the foot of waterfalls and on outside bends of meanders)
Describe the process of attrition
.rocks knock together with force
.rocks gradually become smaller, smoother and rounder
Describe the process of abrasion
.rocks carried by the river are moved towards the river banks and bed
.the rocks scrape along the banks and bed, eroding it
Describe the process of solution
.river water is slightly acidic due to absorption of CO2 and humid acid from vegetation
.carbonate rocks such as limestones dissolve
.eventually rocks dissolve completely into the river water
What is traction?
Large particles are rolled along he river bed by the force of the water at times of high discharge
What is saltation
Small rocks and sand particles are bounced along the river bed (as they are too heavy to be suspended)
What is suspension?
Finer/lighter clay and sand particles are carried along suspended in the water even at low discharges
What is solution
Some minerals dissolve(such as calcium carbonate) and are carried by the water, this requires very little energy
What is load?
Material being transported by a river is called its load
When does deposition occur?
When the velocity of a river slows -decreasing the energy of the water
Where does deposition occur?
At a floodplain, where river meets larger source of water (eg sea)
Why does deposition occur at floodplains?
When a river floods, friction with the land slows water down causing it to deposit its load and lose energy
Why does deposition occur at meanders?
As water swings around the bend friction causes the water to go slower on the inside of the bend and it goes faster on the outside. This causes deposition on the inside of the slope.
Why does deposition occur at the river mouth?
Tidal influences slow river down, the water loses energy, deposits material
How do interlocking spurs form?
.vertical erosion of river bed occurs deepening the v-shaped valley
. Harder rock is harder for the river to erode so it winds its way around the harder rock and eordes the softer rock behind it therefore creating interlocking spurs
How does a waterfall form?
.water runs over alternating bands of hard rock on top of the soft rock beneath it.
.erosion will start to break down rocks through the process of abrasion, hydraulic action and solution
.hydraulic action wears away the soft rock as water runs over it becuas it is less resistant than the hard rock above it.
.over time the soft rock starts to undercut the hard rock
.the hard rock is left unsupported and as a result of this it collapses into the river bed
.rocks that have fallen are either transported away or scrape away the river bed trough the process of erosion . This coupled with continuous friction of water, a dent in the river bed starts to form. This is called a plunge pool
How are gorges formed?
By waterfalls retreating,as erosion continues
Characteristics of meanders?
.slip off slope on the inside of a bend: caused by deposition
. River cliff on the outside of bend: caused by lateral erosion and undercutting
. Deposition on inside, erosion on outside
How does an oxbow lake form?
.water flows over land, water swings round to the outside of the river where there is less friction
. As the river erodes the river bank a bend starts to form known as a meander
.on the inside of the bend the flow is slower resulting in deposition
.the neck of the river grown narrower
.when the neck of the river breaks through the water will take the shortest route and take the straight course
.the neck become sealed off altogether as a result of deposition.
What is a levee?
An embankment of sediment along a river bank. Can be formed naturally or by regular flooding or man made as flood protection
How does a levee form?
During a flood, water passes over surface and increased friction occurs resulting in a slower flow. The heaviest material is deposited first at the closest point to the river because the water has nit got enough energy to carry the materials. The finer sediment is transported and deposited further away from the river. The levee gradually gets higher after successive floods.
What is floodplain?
The relatively flat area forming the valley floor on either side of the river channel which is sometimes flooded
Where are floodplains and levees found?
Lower coarse of the river
What is an estuary?
The tidal mouth of a river where it meets the sea. Wide banks of deposited mud are exposed at low tide.
Define a flood?
When a rivers discharge exceeds its channels volume causing it to overflow
Define discharge
The volume fo water flowing through a river channel, measured at any given point in cubic metres per second
Name 5 physical factors affecting flood risk
Basin size
Soil saturation
Relief
Rock type
Precipitation
Name 3 human factors affecting flood Risk
Urbanisation
Deforestation
Agriculture
How does urbanisation affect flood risk
.more impermeable rock
.less infiltration
. More surface water
How des agriculture affect flood risk
More surface runoff
How does deforestation affect flood risk
Trees take up water, therefore less trees means more water ending up in river Channels
How does rock type affect flood risk
Impermeable rocks dont allow water to pas through them therefore rivers are ore likely to flood as water will not seep into the rocks causing there to be more water flowing over land into the river
How does basin size affect flood risk
If its larger it can stre more water
How does soil saturation affect flood risk
Is the soil is more saturated it can absorb less water meaning there’s more water flowing into rivers therefore increasing discharge
How do reliefs affect flood risk
Steep slopes allow for water to run over the land quickly leaving little time for infiltration resulting in more water in river channels
Examples of hard engineering strategies
Flood relief
Channel straightening
Embankments
Dams
Reservoirs
Examples of soft engineering strategies
Preparation
Planting trees
River restoration
Disadvantages of hard engineering
Not natural
More expensive
Advantages of hard engineering
More effective
Advantages of soft engineering
Natural
Cheaper
Disadvantages of soft engineering
Less effective
How does a dam work
- A large concrete barrier built across a river to hold back its flow.
- Building one causes the land behind the dam to flood creating a reservoir.
- This controls the amount of water downstream by controlling the volume of water being released.
How does channel straightening work
When a meandering section of a river is engineered to create a widened straightened and deepened course. Means it can carry more water and therefore reduce flood risk.
How do embankments work
Raised river banks meaning that more water can be contained in the channel.
How does flood relief channel work
When another channel is built to deliberately move water away from human settlements during times of High discharge.
Name of flood releif channel case study
Jubilee River flood-relief channel
Cost of the Channel
110 million
Length of the jubilee river
11.7km
The cost of repairing after an episode of flooding
680,000
Organisation that funded the jubilee river
EA (environment Ageny)
Year jubilee river was completed
2002
Width of the jubilee river
50m
Year of the worst flooding in the Thames since 1947
2014
How many homes does the scheme protect from flooding
Approximately 3,200
Social issues with the jubilee river
.Puts small businesses under pressure as they cant open when flooded
.high business insurance costs due to flood risk
.ethically, some places protected some not
.too dangerous for paddle boarders
.concrete wires are ugly
Economic issues with jubilee river
.high insurance costs due to risk of flooding
.more affluent places protected, poorer ones not
.most expensive flood relief scheme in the uk
.repairs cost £680000, economic burden
. Due to expenses, government will only fund parti of future flood scenes
Environmental issues with jubilee river
Thames now experiences higher discharge due to merging of two channels
.natural ecosystems affected as algae builds up behind the wires
Why was the jubilee river flood relief channel required?
To take overflow from the Thames and to alleviate flooding to areas surrounding the Thames.
