Physical Landscape Flashcards
Definition of solution
Materials dissolved in water
Definition of suspension
Sand suspended in water
Definition of Traction
Rolling boulders
Definition of saltation
Bouncing pebbles
Definition of freeze-thaw weathering
Water enters a crack, freezes and expands by 10%, when it thaws, more water can enter the crack and so the process continues.
Definition of abrasion
Process where Sand/pebbles in waves rub against the coastline and smooth the surface
Definition of hydraulic action
Waves trap air in cracks in rocks, compressing the air and causing cavitation which expands the crack
Definition of corrasion
Large boulders thrown against the cliff face by the waves
Definition of carbonation
Acids in water dissolved minerals in the rock
How do waves form
Friction from wind blowing over the sea causing ripples that develop into waves
Definition of fetch
It is the distance that wave-generating winds blow across the open water
Why do waves break
As the gradient of the seafloor increases, friction slows the bottom of the wave which causes the crest of the wave to move faster and rise up
(Friction with seabed distorts circular motion, increasingly elliptical orbit as water becomes shallower)
Definition of mass movement
Downward movement or sliding of minerals under the influence of gravity
Key characteristics of constructive waves
Wave crests are far apart
Gently sloping front
Strong swash
Key characteristics of destructive waves
Waves are close together
Steep front
Strong backwash
What is a seawall
- they are at the foot of cliffs/top of beach
- high maintenance
- £10 million per km
- 3-5 metres high
What are groynes
- prevents sediment from being moved down the beach by long-shore drift
- £5000 per metre
- causes higher erosion elsewhere downdrift
What are Rock armour
- rocks against the cliff which forces waves to break therefore absorbing the waves energy
- rocks are expensive to transport
- £1000-£4000 per metre
- obtrusive
What are gabions
- Metal cages filled with rocks
- unattractive
- easy to maintain and last long
- £2000 per metre
What is beach nourishment
- where they build up a beach with sediment from nearby so it blends in
- £3000 per metre
- needs constant maintenance
Dune regeneration
- it is where marram Grass is planted because Dunes are effective buffers for waves and then fenced off so they can grow
- £20 per metre
What is Marsh creation
- allowing low-lying coastal areas to be flooded
- creates habitats
- compensation is given for land so can be expensive
Definition of a drainage basin
An area of land drained by a river and its tributaries
Definition of the source
The start of a river
Definition of the mouth
The end of the river, usually where a river joins the sea
Definition of a tributary
A small stream that joins a larger river
Definition of a confluence
Where a tributary joins a larger river
Definition of a watershed
It is a drainage basin and all the water in the area drains into one body of water
What is a floodplain
They are wide, flat areas on either side of the river in its middle and lower course. They are created by migrating meanders and floods depositing layers of silt to form alluvium
Definition of discharge
Quantity of water that passes a given point in a stream or river bank within a given period of time, measured in cumecs
Characteristics of the upper course
- steep, narrow valleys called V shaped Valleys
- narrow, shallow river, looks fast flowing as areas of rapids
- interlocking spurs
Characteristics of the middle course
- wider valleys
- decreased gradient of landscape
- meanders, oxbow lake, pools and riffles
Characteristics of the lower course
- Side of the valley is called the bluff
- flooding occurs across this valley leaving ‘alluvium’ on valley floor
- levees, estuary, delta
Formation of a waterfall and gorge
- occur when the river flows over resistant rock and then less resistant rock
- see diagram
What is LAG
The time between water landing on the Earth surface and entering a River channel
Causes of flooding both physical and human
Physical:
- precipitation
- rapid thawing
- silting of river channel (shallower)
Human
- urbanisation (impermeable surfaces)
- deforestation (reduces interception)
Hard engineering for managing floods
Dams
Channel straightening
Embankments
Flood relief channels
Soft engineering for managing floods
Wetlands (flood storage)
Floodplain zoning
River restoration
Preparing for floods
Monitoring (satellites), environment agency warnings, individual planning (sandbags).
Outline datchet objections to the Jubilee flood management scheme
- public expense (moving railway and M4)
- cheaper solutions
- it will allow more floodplain development and could become stagnant and mosquito infested
- increased flood risk to Datchet and Staines
- noise and distruption (construction)
Facts about Jubilee food management scheme
- cost environmental agency £110 m.
- first used in January 2003 but some banks failed at only 60% full, costing £3.5 m to repair.
- environment agency said that it protected 400 properties from flooding and disruption was prevented to a further 1000.
- villages east of the confluence e.g. Datchet, were flooded - some residents believe they were worse off.
What facts are there for building the Jubilee flood management scheme
- Thames flooding has return periods Normal cumecs = 60 Every 4-6 years = 350 Every 60 years = >500 Every 100 years = >600 - A flood is scheduled soon
- more people now live on the flood plain
- climate change may make floods more frequent/worse
- River could be a nature reserve and recreation facility
Evidence for worse conditions in Datchet
- 2 river channels means it flows faster through the area than if it flooded before Datchet
- between Thames and Jubilee river there is agricultural land which is being protected instead of residential land
How did the Jubilee scheme work in 2003
- 144 cumecs flowed in Jubilee river only 60% of designed capacity (full = 215 cumecs)
- allowed Thames to be 260 cumecs instead of 404 cumecs
Does the Jubilee river have enough capacity
- many are unconvinced
- 2014, with Jubilee river, Thames still flooded
- claims to hold 285 cumecs but was damaged at 144
Concluding comments on the Jubilee river
2014 showed the area will still flood but Jubilee clearly limited impacts on Maidenhead, Eton and Windsor. However Datchet suffered on a greater scale so will need flood protection.
Banbury flood management reasons why
- 1998 - cost £12.5m , 150 homes and businesses affected
* 2007 - even more properties affected
Management strategies 2017 Banbury
- embankment - 2.9 km long, height of 4.5m
- Raising A361 - improves drainage
- embankments and flood walls - built around Prodrive
- Pumping station - pumps excess water into channel
- biodiversity- New habitats (ponds, hedgerows, trees) to absorb and store excess water. Reservoir (100,000 tons of earth was extracted)
Economic evidence for evaluation of success Banbury
- costs £18.5m
- protects 441 homes and 73 businesses worth £100m
Social evidence for evaluation of success in Banbury
- Raising A361 ensures access routes during flooding
- Quality of life improved e.g. Footpaths
Environmental evidence for evaluation of success in Banbury
- new reservoir and habitats
- biodiversity action plan has created new ponds, trees and hedgerows
Explanation of how river processes changed for Banbury
Encouraging flooding north of Banbury and recovering flow of river through the sluice gates of the embankments reduces river energy and encourages deposition which leads to silting of the channel, reducing the channel capacity and causing more flooding.
Regular dredging is needed to address this.
Factors affecting rate of erosion
- energy of waves
- size and shape
- resistance of the coastline
- gradient of sea floor
Example of Mass movement
Rotational slip:
- impermeable under permeable rock
- water saturates permeable
- slips in a rotational manner
How are levees formed
When deposition raises the riverbed so the channel cannot carry as much water, so during flooding, the water flows over the side of the channel and deposits on the banks raising the height of the levees
