Physical Lanscapes in the UK - Rivers Flashcards
What does erosion form in the upper course of the river?
Interlocking spurs
Waterfall & Gorges
What does erosion in the middle course of the river form?
Meanders
Ox-Bow lakes
What does erosion in the lower course of the river form?
Levee
Flood Plain
Estuary
Interlocking Spurs
- Vertical erosion creates steep-sided, v-shaped valley
- Freeze thaw weathering widens the valley
- Hillsides interlock with each other as river winds around them
Waterfall and Gorge
- Water runs over alternating of hard rock on top and soft rock below
- Erosion breaks down rocks
- Hydraulic action wears away soft rock - less resistant, soft rock undercuts hard rock = overhang
- Hard rock is left unsupported and collapses into river bed
- Rocks are transported downstream or abrasion wares away ar river bed = plunge pool
- This process repeats and waterfall retreats backwards → steep-sided gorge.
Meanders
- Fastest velocity swings round the outside bend of a meander which erodes bank - forming a river cliff = water is deep = less friction
- On the inside of the bend, velocity is lower and deposition occurs - slip of slope
- Over time lateral erosion of outside bend widens river
Ox-Bow Lake
- On the inside of the bend flow is slower so sediment is deposited
- The neck of the river grows sharper
- The neck of the river breaks through, river takes shortest course straight
- Meander becomes sealed off as a result of deposition — oxbow lake
- Ox bow lake can dry up - vegetation grows leaving a scar
What is a levee?
A raised bank next to the river bank
Levee
- During a flood water passes over a surface —> increases friction = slows flow
- Heavy material deposited early, lighter sediment travels downstream
- Levee gradually gets higher after more floods = more deposition
Floodplain
- Build up of sand, silt and clay (deposition + transportation) leads to formarion of a flat piece of land either side of the levees.
- Every time a river floods, deposition builds up the floodplain.
- width of flood plain is derermined by amount of lateral erosion.
Estuary
- An estuary is where the river meets the sea
- When sea retreats, volume of water is reduced
- Less water means river deposits silt to form mudflats (important for wildlife)
Physical factors affecting flood risk
Relief - Steep slopes means water runs quickly
Soil saturation - Soil can no longer absorb water
Rock type - Impermeable rock means water is not absorbed
Rainfall - Rainstorms can lead to flash floods
Basin Size - Amount of water a river can store
Human Factors affecting Flood risk
Deforestation - Trees intercept water
Urbanisation - Building areas in risk of flooding - impermeable rock
Agriculture - soil is left unused + exposed = surface run off
What do hydrographs show?
The relationship between precipitation and discharge
What is river straightening?
Widens, Deepens, Straightens course to carry more water
Pros and cons of river straightening?
+ Increases basin size of river
- Speed of river increases
Pros and cons of embankments?
+ More water held in river without flooding banks
- Expensive/Less attractive/Disrupts ecosystem
What is embankments?
Raised river banks so water is contained within channel
What is Flood relief?
Another channel is built, moves water away from settlements
What are Dams & Reservoirs?
Large concrete barrier that holds back flow
Pros and cons of Flood relief
+ Effective depending on flood severity
- Where channel meets river flooding occurs
Pros and cons of Dams & Resovoirs
+ Generates energy/Attracts tourists
- Expensive/traps sediment/habitats ruined/people displaced
What are the three types of flood warning?
Flood watch - Flooding of low land and roads
Flood warning - Threat to homes & Businesses
Severe flood warning - EVACUATE
What is planting trees?
A method of interception
Pros and cons of Planting trees
+ Slows flow of water towards river
- Takes space, long time to grow
What is flood plain zoning
Holds water during flood events
Protects people and houses
What is River Restoration
Move debris + Logs
Natural methods - beavers
pros of River restoration
Debris and logs slow down flow of water
What is the river case study?
The Jubilee River Flood Channel
What is the Jubilee river flood channel?
Acts as a flood relief channel for the River Thames
What does the Jubilee river flood channel do?
controls and diverts water during times of high flow
Reduces flood risk
How much did the Jubilee river flood channel cost?
110 million
What are the social impacts of the Jubilee river flood channel?
Paddle boarders where promised navigable river - In reality it is two dangerous to cross
Concrete weirs are ugly when river is at normal flow
Some properties are protected others are not - 3,000 homes in Eaton + Windsor (affluent areas)
What are the economic impacts of the Jubilee river flood channel?
Small business are under pressure - can’t open during floods and insurance is to expensive
Most expensive flood relief scheme in the UK
Additional repair damage
What are the environmental impacts of the Jubilee river flood channel?
Extensive flooding where channel joins Thames - roads, buildings, fields, habitats and the environment suffered
Algae collects behind the weirs and slows water flow
Disadvantage of the Jubilee river flood channel
The Thames experiences higher discharge due to the merging of the channels upstream
When was there serious flooding of the Jubilee river flood channel
2014
Upper course characteristics
Steep-Sided walls
Narrow channel
Fast flow
Lower course Characteristics
Shallow sides
Wider channel
Lower course characteristics
Flat
Wide channel
What does Bradshaw model show?
Velocity, width, depth increase downstream
Why is heaviest material deposited first
Requires more energy
Where is the most deposition and why
Lower course
River slows down as it loses its energy
Lateral erosion
Sideways erosion of river banks
Vertical erosion
Downwards erosion of river bed
Hydraulic Action
Force of river causes air to be trapped in cracks
Abrasion
Rocks wear down the river beds and banks
Attrition
Rocks bash against each other = smooth
Solution
Soluble particles are dissolved in river
Traction
The rolling of boulders and pebbles along the river bed
Saltation
Particles bouncing down the river bed
Suspension
Fine solid material held in water
Solution
Soluble particles dissolved into river
What are upper course characteristics of the river Severn?
V-shaped valley
Waterfalls
Meanders - Kempsey in Worcestershire
What are lower course characteristics of the river Severn?
Meanders - Gloucestershire
Large Mouth
Mudflats & Sandbanks