P1C Rivers and Coasts (Physical Landscapes UK) Flashcards
Describe river erosion processes (4)
- hydraulic action- erosive force exerted by water
- attrition - sediment particles knock against each other and break into smaller/more-rounded pieces
- abrasion - river bedload grinds against the bed+sides
- solution - minerals dissolved into water
Describe river transportation processes (4)
- traction - larger boulders/stones roll along river bed
- saltation - stones bounce along river bed
- suspension - smaller clay/silt/sand particles are carried without contact with river bed
- solution - dissolved minerals carried in water
Define deposition
when a river loses its energy or volume, resulting in materials being transported to settle
Define the two types of river channel erosion
- lateral - widens river channel
- vertical - deepens river channel
describe the long profile of a river in the upper course
- (erosion) mostly vertical erosion by hydraulic action+ abrasion
- (transport) mostly traction - large boulders moved
- (deposit) - largest boulders deposited
- steep gradient at the source
describe the long profile of a river in the lower course
- (erosion) very little erosion - only lateral erosion on outside of river bends
- (transport) mostly suspension - lots of small particles
- (deposit) deposition mainly occurs here
- flat gradient, reduces quickly in height as slope reduces
Describe the cross profile of a river in the upper course
- (channel) narrow and shallow
- (valley) clear v-shaped valley
Describe the cross profile of a river in the lower course
- (channel) wider and deeper
- (valley) widened, flood plains at sides of river
describe how a waterfall forms a gorge
- river flows over hard rock
- hydraulic action+ abrasion erodes soft rock underneath
- hard rock cap layer/overhang collapses into plunge pool
- hydraulic action+ abrasion+ attrition cause particles to become smaller and are washed downstream by traction+ saltation+ suspension
- as the waterfall retreats up river it leaves behind a steep vertical-sided gorge
describe gorges
- very steep valley sides
- river channel takes up most of valley floor
- turbulent, fast-flowing water
- boulders in river bed
describe interlocking spurs
- steep sides
- winding river
- narrow valley floor
describe how meanders form + properties
- river flows faster on outside of bend due to centrifugal force - results in erosion (hydraulic action/abrasion/attrition) on outer bank + undercuts to create a river cliff
- deposition occurs in slow-moving water on inside of bend - slip-off slope of sand+shingle forms
describe how oxbow lakes form
- caused by continuous erosion of outer bank of a meander
- river eventually cuts through narrow neck
- deposition isolates a portion of the river as an oxbow lake
- over time may infill with sediment to form a scar
describe how levees and flood plains form
- during a flood the heaviest/most coarse sediment is deposited at sides close to river as more difficult to transport - forms levees
- finest sediment is carried further+ deposited to form a flat flood plain
- river bed deposits build up+ raise the level of the river - increases chance of a flood
describe tidal estuaries
- formed by the sea level rising+ filling an existing river valley
- river carries sediment downstream+ deposits it at lower course of the river as it stops flowing when it reaches the sea
- mud flats form at bottom of estuary bed - visible at low tide
- sand bars form due to the deposition
describe the use of dams and reservoirs
regulate the water flow and hold back the water in a reservoir
describe the use of channel straightening
a meandering section of a river is engineered to be wider and straighter, shortens distance water travels and speeds water away from vulnerable areas (cities)
describe the use of embankments
raising the banks of either side of the river channel (sometimes covered in grass/flowering plants)
describe the use of flood relief channels
an extra channel bypasses and adds capacity to the main river, controlled by a weir/flood gate
describe benefits and costs of dams/reservoirs
/ boosts tourism, highly effective, provides hydroelectric power, source of drinking water, new habitats
X flooding valley above dam displaces people, expensive, interferes with migration of fish, can destroy habitats, have to be dredged
describe benefits and costs of channel straightening
/ moves water away more quickly/ improves efficiency, makes boat navigation easier, home owners no longer worry about flooding so invest in properties
X habitats destroyed, can cause flooding lower downstream, expensive, may use unattractive concrete linings
describe benefits and costs of embankments
/ cheaper than other hard engineering, provides habitats, used for walking paths, increases river’s carrying capacity
X if breached water lies on surrounding land, needs continual maintenance, access to river is difficult for fishing/boating
describe benefits and costs of flood relief channels
/ moves water away more quickly, home owners no longer worry about flooding so invest in properties, new habitats created
X habitats changed/destroyed, can cause flooding lower downstream, expensive, take a long time to build
describe causes of flooding (4)
- prolonged/heavy rainfall - soil becomes saturated leading to runoff
- geology - impermeable rocks cause surface runoff, increases river discharge
- land relief - steep-sided valleys cause water to flow quickly into rivers causing greater discharge
- land use - impermeable building materials (tarmac/concrete) prevent infiltration+ cause surface runoff
describe the uses and pros/cons of flood plain zoning (soft engineering for floods)
process of stopping land near river from being built on
/ low cost, preserves green spaces, reduces amount of impermeable surfaces
X housing shortage (fewer places to build)
describe the uses and pros/cons of flood warnings (soft engineering for floods)
warnings give people time to move possessions+ evacuate
/ very cheap, people+properties can be saved
X only effective if people respond
describe ways to prepare houses for floods (7)
- raise properties off ground
- tiled floors
- flood guards at doors
- waterproof coatings
- raised power sockets
- wall-mounted tvs
- no fitted carpets
describe the uses and pros/cons of planting trees (soft engineering for floods)
increases interception+evaporation+ transpiration+filtration, reduces run-off
/ more carbon dioxide absorbed, adds variety to landscape
X loss of grazing land
describe the uses and pros/cons of river restoration
a river that has previously been hard engineered is restored to a natural channel
/ new wetland habitats, slows down water flow and keeps it in the area for longer - reduces flooding, aesthetically pleasing
X loss of extra farm land
describe the location of a UK town at risk of flooding and its causes of flooding (5) (case study)
Boscastle, north coast of Cornwall, 2004
* torrential rain/storm - 200mm rain fell in 24hrs - ground is saturated so increases runoff
* trees were cut down - increases runoff
* small drainage basin - water reaches town quicker
* steep v-shaped valley sides - fast water velocity
* settlements built downstream on narrow flood plain
describe the impacts of flooding at Boscastle (case study)
- houses+bridges destroyed
- businesses destroyed eg. visitor centre, tourism devastated
- people worried+ evacuated
- 116 cars washed into sea
- economic damage - fall in house prices, £300m lost
describe the responses to the flood at Boscastle (case study)
- channel was widened+ deepened+ straightened
- bridges made wider+ higher to allow more water through
- raised car park+ built with a permeable material - cars less likely to be swept away/ reduces runoff
- dead trees+ trees close to river removed - prevents them from being swept away+ causing blockages
- land use zoning - prevent construction on river bank so residential buildings protected
-> planning+protection but unable to predict
describe what causes waves (3)
- wind speed
- wind duration
- the fetch - size of area/distance wind is blowing over
describe constructive waves
- created in calm weather, less powerful
- deposit material on the beach
- swash is stronger than backwash
- low wave height
- forms a gently sloping, sandy beach
describe destructive waves
- created in stormy weather
- erode the beach+cliff
- backwash is stronger than swash
- big+strong waves with high frequency
- forms a steep, pebble beach
- offshore bar forms as material eroded is deposited at bottom of sea bed
describe types of weathering (3)
- chemical/carbonation - rainwater dissolves calcium carbonate rocks (limestone/chalk);
the iron in rocks oxidises/rusts - mechanical - due to extreme temps (freeze-thaw, heating+cooling);
when sea spray gets into cracks in rock then evaporates to form crystals that push the crack apart - biological - plant roots grow into rock cracks and push them apart
describe types of cliff erosion (7)
- freeze-thaw erodes the top of the cliff
- biological - plant roots grow in rock cracks+expand
- corrosion from crystalised salt in rock cracks
- hydraulic action when water gets into cracks
- solution - rock eroded by acidic seawater
- attrition - rocks smash into one another
- abrasion - rocks grind against cliff
describe how headlands+ bays form
- discordant coastline - alternating layers of hard rock (chalk/limestone) +soft rock (sand/clay) perpendicular to coast
- waves erode soft rock more quickly by abrasion+attrition - beaches form in bays due to longshore drift+deposition
- headlands of hard rock jut out into the sea
define hard and soft engineering
hard - large scale construction, expensive, tries to prevent flooding
soft - more natural/ environmentally friendly, reduces impact of flooding with less intervention
describe the formation of spits and bars
- sediment is carried by longshore drift
- when there is a change in the shape of the coastline, deposition occurs and a long thin ridge of material forms a spit
- a hooked end forms if there is a change in wind direction
- waves cannot get past spits so silts are deposited in the sheltered salt marshes/ mud flats behind
- a bar forms when the spit connects with land
describe the formation of a sea stack/ stump
- a crack in the cliff is continually eroded by hydraulic action+ abrasion until a cave forms
- more rock is eroded at the base to form an arch, and chemical+ freeze-thaw weathering occurs at the rock above
- the rock above is weakened and collapses leaving an isolated pillar of rock and forming a stack
- the stack is eroded to form a shorter stump
describe the formation of sand dunes
- obstacles (driftwood) are dropped on beach
- onshore wind blows sand onto beach which is trapped by obstacles
- plants (marram grass) grow+ stabilise dune with roots, so more sand is trapped
describe the use and cost of sea walls
£5000 per m, curved face to deflect waves back to sea, made from concrete/stone, build-up of beach material at base of sea wall (toe protection)
describe the use and cost of groynes
£1000 per m, fence-like structure constructed at right angles to coast, traps material transported by longshore drift
describe the use and cost of rock armour
£1500 per m, large boulders placed in front of a cliff or sea wall
describe the use and cost of gabions
£110 per m
describe benefits and costs of sea walls
/ protects base of cliff from erosion, can prevent coastal flooding
X expensive, unattractive, makes access to beach difficult
describe benefits and costs of groynes
/ prevents movement of beach material by longshore drift, allows the build-up of a beach, more natural-looking beach for tourists+ residents
X unattractive, makes access to beach difficult, may cause issues further along the coast
describe benefits and costs of rock armour
/ absorbs energy of the waves, can be local rock so more natural-looking
X unattractive, makes access to beach difficult, requires maintenance
describe benefits and costs of gabions
/ absorbs energy of the waves, can be local rock so more natural-looking, relatively cheap
X unattractive, makes access to beach difficult, expensive to rebuild
describe pros+cons of beach nourishment
sediment is replaced from other sources/ sediment from downdrift is moved updrift by lorries+dredgers
/ wider beach attracts tourists, looks natural
X requires maintenance
describe pros+cons of beach reprofiling
transfer of material from lower to upper beach to make sides steeper
/ residential areas behind beach are protected, looks relatively natural
X steep+high beach can be uninviting/restricts access
describe pros+cons of dune regeneration
restoring sand dunes using vegetation or fences to stabilise dunes+ provide a barrier to collect sand
/ protects residential areas behind beach, cheap as local plants are replanted
X requires maintenance, beach is inaccessible during plant growth, fertilisers used
describe the process of mass movement
- rain/flood saturates permeable rock on surface making it heavier
- waves or river erodes base of the slope by hydraulic action+abrasion
- the weight of the permeable rock weakens the impermeable rock underneath so it collapses
- debris at base of cliff/slope is transported away by waves/river
describe types of coastline (2)
- concordant - alternating hard+soft rock layers parallel to coast - forms a smooth coast
- discordant - alternating hard+soft rock layers - form headlands+bays due to erosion - jagged coast
describe key terms used in a flood hydrograph (6)
- peak rainfall - the hour of greatest rainfall during a storm (shown on bar chart)
- peak discharge - the time of maximum discharge in river (shown at top of line graph curve)
- rising limb - period of rising river discharge following rainfall
- falling limb - period of falling river discharge
- lag time - time between peak rainfall and peak discharge
- normal flow - base flow of the river (shown at bottom of graph)
describe the location of a UK town and the coastal realignment scheme used (case study)
- Medmerry, coast of south England
- used managed retreat - a breach was made in the shingle bank to allow land behind to be flooded
- clay embankment built around intertidal area to contain floodwaters
describe pros+cons of the coastal realignment scheme used at Medmerry (case study)
/ protects properties+water treatment plant+ mobile home park, created salt marshes good for wildlife habitats+ cattle farming, nature reserve for intertidal habitats, cheaper than hard engineered sea defences
X agricultural land lost, landowners require compensation, disturbs existing species’ habitats
