River processes and pressures Flashcards
What is the gradient like in the upper course?
Steep
What is the discharge like in the upper course?
Small
What is the depth like in the upper course?
Shallow
What is the channel shape like in the upper course?
Narrow, steep sides
What is the velocity like in the upper course?
Quite fast
What is the valley shape like in the upper course?
Steep sides
What features are found in the upper course?
Waterfalls, interlocking spurs
What is the gradient like in the lower course?
shallow gradient
What is the discharge like in the lower course?
Very large
What is the depth like in the lower course?
Deep
What is the channel shape like in the lower course?
Flat floor, gentle slopping sides
What is the velocity like in the lower course?
Very fast
What is the valley shape like in the lower course?
Flat, gentle slopping sides
What features are found in the lower course?
Meanders, floodplains, levees and ox-bow lakes
What is the gradient like in the middle course?
Less steep
What is the discharge like in the middle course?
Large
What is the depth like in the middle course?
Deeper than the upper course
What is the channel shape like in the middle course?
Flat, steep sides
What is the velocity like in the middle course?
Fast
What is the valley shape like in the middle course?
Flat, steep sides
What features are found in the middle course?
Meanders and floodplains
What are the four main processes of erosion?
Hydraulic action
Abrasion
Attrition
Solution
What is hydraulic action?
The force of water on the bed and banks of the river removes material
What is attrition?
The load that is carried by the river bumps together and wears down into smaller, smoother pieces
What is abrasion?
Material carried by the river rubs against the bed and banks and wears them away
What is solution?
Some rock minerals dissolve in the river (limestone and chalk) and are carried along in the flow
What are the four main types of transportation?
Traction
Saltation
Suspension
Solution
What is traction?
Large boulders roll along the river bed
What is saltation?
Smaller pebbles are bounced along the river bed, picked up the dropped as the flow of the river changes
What is suspension?
Finer sand and silt particles are carried along in the flow, giving the river a brown appearance
How are waterfalls formed?
More resistant rocks lies over less resistant rock
Less resistant rock is eroded forming a step
More resistant rock is undercut forming an overhang
Overhang is not supported so rock falls into water
Powerful fall of water erodes plunge pool with fallen rocks
Waterfall retreats upstream
How are interlocking spurs formed?
The river naturally flows from side to side, around ridges in valley sides (spurs). These spurs become interlocking with those on the other side of the valley
What are meanders?
Bends in the river’s course
Where are meanders found?
Lower course
Where are waterfalls found?
Upper course
Where are interlocking spurs found?
Upper course
How are meanders formed?
As a river bends the current is slower on the inside so it deposits sediment whereas on the outside it is faster so it erodes the bank
How does an ox-bow lake form?
A river creates a meander, due to the river’s eroding the bank. After a long period of time, the meander becomes very curved, and eventually the neck of the meander becomes narrower and the river cuts through the neck during a flood, cutting off the meander and forming an oxbow lake.
Where are ox-bow lakes found?
Lower course
How are levees formed?
When a river floods it deposits the biggest and heaviest particles on the bank forming floodplains
Increased deposition causes the river bed to raise
After many floods the banks build to form levees
Where are levees found?
Lower course
What is a delta?
Overtime sediment builds up to create an almost flat area of new land
What happens to the river because of deltas?
The river moves very slowly over the new flat land so its channel fills up with sediment so it has to split into streams
What are the two types of slope processes?
Soil creep and slumping
What is soil creep?
Particles of soil slowly move down the sides of valleys under the influence of gravity
What is slumping?
Valley sides are eroded by the river making the sides steeper and increasing downward movement of material
What can trigger slumping?
Heavy rainfall
What are the sides like of rivers flowing of resistant rock?
Steeper
What are the sides like of rivers flowing of less resistant rock?
Gentle slopes
What is the transportation rate of rivers in a wet climate?
It is greater as the energy of water is greater so wet climates transport more material
What is the amount of discharge in a wetter climate?
Greater discharge
What is the amount of discharge in a drier climate?
Less discharge as there is more evaporation
The greater the discharge the higher the what?
The higher rate of transportation
What type of weathering is greater in a colder climate?
Freeze-thaw
When is the erosion rate greater?
Where discharge and energy of the river is greater
Is the erosion greater in a hotter or wetter climate?
Wetter
What does the rate of erosion effect?
Shape of river valley and amount of sediment
What do storm (flood) hydrographs show?
How a river responds to a rainstorm
How do you find the lag time?
The difference in time between the peak of the rainstorm and the peak of the discharge
What does the bar graph show?
The amount of rainfall in mm
What does the line graph show?
The rivers discharge
What does a shorter lag time and steeper rising limb show?
Greater risk of flooding
What human activities contribute to flooding?
Urbanisation
Land-use change
Building on floodplains
Deforestation
How does geology effect flooding?
More resistant rock will absorb lees water so run-off will be greater and faster
How does soil type effect flooding?
More impermeable soil (clay) will absorb less water so run-off will greater and faster
How does vegetation effect flooding?
Less vegetation will mean the rain will not be intercepted and surface run-off will be greater and faster
How does slope effect flooding?
Steeper slopes cause faster surface run-off so more water reaches the river quicker
How does drainage basin effect flooding?
A wide drainage basin with lots if tributaries close together means water enters the river quicker, meaning the rising limb is steeper and the lag time shorter
How does antecedent conditions effect flooding?
When the ground is more saturated with water, further rain flows as surface run-off
What are the threats of flooding on people?
Damage to home
Damage to farmland
Death and injury
Damage to businesses
What are the threats of flooding on the environment?>
Damage to wildlife/ their habitats
Damage to vegetations
Polluted floodwater damaging the land
How has climate change increased flooding?
Increased frequency of storms
Increased periods of hot/dry weather
Increased periods of extreme cold
How does increased storm frequency increase flooding?
More periods of heavy rainfall so more rainfall enters the river and more antecedent conditions
How does increased periods of hot/dry weather increase flooding?
It bakes the soil so when it does rain it can’t be absorbed so it runs as surface run-off
How does increased periods of extreme cold increase flooding?
Freezes the soil so water runs as surface run-off as it can’t be absorbed
What are hard engineering methods for managing flood risk?
Embankments and levees
Flood walls
Dams and reservoirs
Flood barriers
What are the advantages and disadvantages of embankments and levees?
Use natural materials so the look natural
May burst causing widespread flooding
What are the advantages and disadvantages of flood walls?
Require minimum maintenance
Block the view of the river
What are the advantages and disadvantages of dams and reservoirs?
Able to regulate and control the flow of water
Very expensive
What are the advantages and disadvantages of flood barriers?
Can be moved to where needed and quickly erected
Don’t provide long lasting protection
What are the soft engineering methods for managing flood risk?
River restoration
Washlands
Floodplain retention
Plant trees (afforestation)
What are the advantages and disadvantages of river restoration?
Can reduce flooding downstream
People living there may not want land use to change
What are the advantages and disadvantages of washlands?
Restricts economic development
What are the advantages and disadvantages of floodplain retention?
Provides somewhere for floodwater to go
Restricts economic development
Attractive and provides place for leisure and recreation
What are the advantages and disadvantages of planting trees (afforestation)?
Increased infiltration
Not suitable fort all locations
What are one of the physical causes of flooding in Tewkesbury?
Two of the largest rivers in the UK meet in Tewkesbury- the Severn and the Avon
What happens before the Severn reaches Tewkesbury?
It travels through many mountains and hills so steep slopes cause faster surface run-off
Why does the drainage basin effect the Severn and flooding in Tewkesbury?
Because lots of tributaries flow into the river before it reaches Tewkesbury
Why is the Severn’s discharge often high before it reaches Tewkesbury?
Because of snowmelt
Why has urbanisation increased flooding in Tewkesbury?
Caused the town to grow so there is less permeable surfaces to absorb water
Why has building houses increased flooding in Tewkesbury?
As houses have been built on a floodplain making them very vulnerable to flooding
Why has field drains increased flooding in Tewkesbury?
They improve farmland but they move water into the tributaries very quickly
