Paper 1 - River Landscapes and Processes Flashcards
What is the Watershed?
The outline of the Drainage Basin
What is the Drainage Basin?
The area over which a river covers
What is the River Source?
Where the river begins, or comes from
What is a Confluence?
Where two rivers are stream join to create a wider channel
What is a Tributary?
Where a smaller river or stream joins the bigger, man channel
What is the River Mouth?
Where the river meets the sea
Why does a river’s velocity increase as it travels dowstream?
- There is change in gradient
- More water from confluences/tributaries
- Less friction of the river bed due to erosion
Why does gradient decrease as the river travels downstream?
- Not enough water at the source to have the power to erode the river bed
- As confluences/tributaries join, discharge increases
- River gains power and can now erose the river bed to a flatter gradient
What happens to load quantity and why?
- More load in the river
- More water due the confluences/tributaries
- Brings more sediment
- Has more velocity so has enough energy to pick up more load
What happens to load size? And why?
- Load gets smaller
- River has more power from more water
- Attrition can occur
What is Weathering?
The breakdown and decay of rock by natural processes
What is Erosion?
When water wears away rock and soil
What is Transportation?
When a river picks up and carries material
What is Deposition?
When the water doesn’t have enough energy to carry it’s load, so ‘drops’ it
What is Mass movement? Why does it happen? What can speed it up?
- The movement of rocks and soil downslope
- Due to gravity
- Sped up by weaker rocks and steep slopes
What are the three types of mass movement?
- Soil Creep
- Sliding
- Flows
What is Soil Creep?
Individual particles of soil move slowly down the slope due to gravity
What is Sliding?
The material moves rapidly down the slope in one go
What is Flow?
When the soil and rock is mixed with water and flows like a liquid downhill
Name three types of weathering
- Biological
- Chemical
- Mechanical
Name 4 types of erosion
- Hydraulic action
- Abrasion
- Attrition
- Solution
What is mechanical weathering also known as?
Freeze-thaw weathering
What is chemical weathering also known as?
Acid rain
Describe mechanical weathering
- Cracks in rock get filled with water
- Temperature falls below 0°C and water freezes and expands forcing the crack open
- Ice melts when temperature returns to above 0°C and runs away
- Process repeats over time and cracks became wider until the rock breaks up completely
Describe chemical weathering
- Chemicals mix with water and are evaporated
- Slightly acidic mixture falls as acid rain
- Dissolves the rock (especially limestone)
Describe biological weathering
- Seeds get into cracks in the rock and grow into trees
- Roots widen and break off bits of rock
- Animals burrowing
What is Hydraulic action?
The sheer force of the water hitting the river bed and banks, wearing them away
What is Attrition?
Load particles collide with eachother, making their edges smooth and rounded, as well as smaller
What is Abrasion?
Rocks carried along by the river scrape and wear down the river bed and banks
What is Solution?
River water is slightly acidic and can dissolve some rocks and minerals that come into contacts (limestone and chalk are most effected)
Where can you find a V-shaped valley and how is it formed?
- In the upper course
- River has little discharge so is mostly in contact with river bed and banks (lots of friction) so river moves slowly
- The water’s energy is used to erode the bed downwards - gravity - so the sides are steep
Where can you find interlocking spurs? How are they formed?
- They are in the upper course
- Naturally occurring areas of hard rock prevent the river from travelling in a straight line
- the river is in the uppercourse so doesn’t have the energy to erode through it, so goes around it
Explain how Waterfalls are formed
- when a river crosses over a band of hard rock on top of softer rock, the softer rock is eroded quicker by abrasion and hydraulic action
- An overhang is created by the the recession of the back wall where the ledge has been undercut; a plunge pool forms as the bottom of the ledge
- The water’s weight becomes too heavy for the harder rock & gravity, so it breaks off in large angular rocks and collapses; there is lots of attrition and abraison on the fallen rocks and the hydraulic action from the water’s force
- Over time the process repeats and the waterfall retreats backwards/upstream - a steep sided gorge is formed
In the middle course what direction of erosion is dominant? Why?
- More lateral (side-to-side) erosion
* Due to flatter land
List features of the outside of a bend in the middle course
- Faster moving water
- More erosion
- River cliff formed
- Deeper water
List the features of the inside of a bend in the middle course
- Slower moving water
- More deposition
- Slip-off slope or river beach formed
- Shallow water
Describe the formation of an Oxbow Lake
- Meander bends become very very large
- The inside bends on the meander become very close together - the ‘neck’ thins
- During a time of flood or increased discharge, the river can cut through the gap and former a straighter channel
- Over time the river will deposit thin load called ‘Alluvium’ that cuts off the bend
- It forms a body of water that looks much like a bullring, or ‘Oxbow’
List some features of the lower course
- Flattest part of the river
- Channel is wide and deep
- Faster flow due to less friction
- Load is small
What is a floodplain?
The area of flat land either side of a river in the lower course
What is a Leeve?
A natural embankment of sediment formed by depositon along the banks of the river
What are the 4 types of transportation?
- Traction
- Saltation
- Suspension
- Solution
What is Traction?
Bigger heavier rocks roll along the river bed
What is Saltation?
Smaller rocks bounce across the river bed
What is Suspension?
Light materials are suspended and can float in the water and be carried downstream
What is Solution?
Particles are dissolved and carried downstream
What is Lag Time?
The difference between peak rain fall and peak discharge - the a mouth of time the water takes to travel to the river, this will be greater in permeable surfaces and less of impermeable surfaces
What is an impermeable surface?
A surface that does not let water ‘permeate’ it - runs over it without absorption - e.g. concrete
What is a permeable surface?
A surface that does absorb water - e.g. soil
CASE STUDY: Floods - Boscastle) 1) When were they?
Mid-August, 2004
CASE STUDY: Floods - Boscastle) 2) List two facts about the floods
- It had had 5 great floods earlier
* 2 million tonnes of water flowed through Boscastle in 1 day
CASE STUDY: Floods - Boscastle) 3) List a few causes of the flooding
- Boscastle is at the confluence of 3 rivers
- 200mm of rain fell in 1 day
- The ground was saturated from previous rainfall
- It has lots of impermeable rock
CASE STUDY: Floods - Boscastle) 4) List a few effects of the flooding
- Loss of income from tourism
- Loss of habitat
- Loss of businesses and communications
- Tress uprooted
- Cars/vans/caravans washed into the sea
- Buildings flooded and destroyed
- Debris widely scattered
CASE STUDY: Floods - Boscastle) 3) List a few responses to the flooding
- Drainage improved
- Cars removed from habour
- Car parks raised
- Buildings searched
- Water gauging stations installed
What is Hard Engineering?
Controlling floods by building defences out of concrete
What is Soft Engineering?
Using more natural approaches to managing floodwater
What type of Engineering technique is Embankments?
Hard Engineering
What type of Engineering technique is Channelisation?
Hard Engineering
What type of Engineering technique is Flood Relief Channels?
Hard Engineering
What type of Engineering technique are Dams and Reservoirs?
Hard Engineering
What type of Engineering technique is Washlands?
Soft Engineering
What type of Engineering technique is River Restoration?
Soft Engineering
What type of Engineering technique is Floodplain Zoning?
Soft Engineering
What type of Engineering technique is Afforestation?
Soft Engineering
What is Embankment?
High built banks on or near the river bed
What is Channelisation?
Deepening and/or straightening the river channel
What are Flood Relief Channels?
Extra channels built to redirect water away from the river
What are Dams and Reservoirs?
Barriers that hold back water in artificial lakes
What are Washlands?
When areas on the floodplain are allowed to be flooded
What is River Restoration?
Letting the river flow it’s original course - restoring meanders, remove man made embankments
What is Flood-plain Zoning?
Government allocate areas according to flood risk (controlling the land use)
What is Afforestation?
Planting more trees to absorb excess water
Evaluate the use of Embankments
+ Stop water from spreading into areas where it could cause problems, i. e. Housing
+ Can be made out of earth and grass so blend in with environment
- Floodwater can overflow and be trapped behind them
- Can burst under pressure, causing damage
Evaluate the use of Channelisation
+ Allows more water to run through the channel and more quickly taking it away from places of risk
- Water is taken downstream so can put other places at risk
- It looks unnatural
Evaluate the use of Flood Relief Channels
+ Can accommodate high flows so it will not overflow banks
- Can be unsightly
- Not always needed
- Very expensive
Evaluate the use of Dams and Reservoirs
\+ Long lasting \+ Can produce Hydroelectric power \+ Provide local water supply \+ Can be used for Water sports - Expensive - Force people to leave their homes - Ruin the environment - Growth of Algae
Evaluate the use of Washlands
\+ Safe place for floodwater to go \+ Slows floodwater down \+ Improves natural sedimentation process \+ Soil structure improved - Limits land use
Evaluate the use of River Restoration
\+ Natural course \+ Slows rivers down \+ More attractive \+ Provides more natural habitats - Some flood banks still required, e.g. floodplain retention - changes in land use
Evaluate the use of Flood-plain zoning
+ Prevents building houses and businesses on high risk zones
+ Open space and leisure/recreation on floodplains - less costly to restore
- not best fitted for land use type
- Floodplains are attractive places to build
Evaluate the use of Afforestaion
+ Water takes longer the reach the channel
+ Low costs
+ enhances environmental quality
- If conifers planted, it will make the soil more acidic
- Prevents the land being used for other things
