5. Unit 1: Topic 5: Contrasting Coasts
Terms in this set (60)
Types of coastal erosion:
(Breaking down of material and transportation)
to see some good animation examples of the erosion types
Attrition: material hits each other in the waves which breaks it up and smooths it off
Abrasion: the material is thrown at the cliff foot which wears it away
Hydraulic action: as water enters a crack in the cliff it compresses the air inside, forcing it back into the rock which breaks the rock apart resulting in a larger crack or bits of rock coming away from the cliff
Solution: contact with the water (due to acidic content)
(Breaking down of material)
Freeze- thaw: water gets into a crack in the rock > overnight the temperatures drop- causing the water to expand > which forces the rock apart
Biological: plants that grow in cracks cause the rock to break apart eventually because their roots force the crack to widen as they grow, also, animals burrowing can cause weathering
It starts with water getting into a crack > then it turns into a cave > then an arch > then a stack > and then a stump...
Local example = the Needles
Discordant/ Concordand coastlines (Dorset example)
Discordant: layers of hard and soft rock which runs vertically against the coastline, forming headlands and bays
Concordant: layers of hard and soft rock which lie parallel against the coastline, can form coves
Bird's eye view:
Waves bend around the headland- causing erosion to occur on th sides
Key terms: Backwash
Movement of a wave retreating back to sea, away from the beach
Sheltered area of coastline made from soft rock
An approach that allows natural processes to take their course without any intervention
Breaking down of rock and sediment and transportation
Distance a wave travels before hitting the coastline
Heavily managed area of the coastline e.g. sea walls
Outcrop of land at sea made from hard rock
Approach to environmental management that treats the whole area as an interrelated system
Process of sediment moving along the coastline
The down slope movement, by gravity, of soil and/or rock by the process of slumping, falling, sliding and flowing- only need a 40* slope for a land slide
Sand and sediment which is attatched to the coastline but sticks out at sea
Reorganisation of coastal defences that is often part of managed retreat
Weathering of rock and the impacts of wind and rain
Movement of a wave onto a beach
Breaking down of material (without tarnsportation)
Isle Of Wight Case Study:
Management on the Island:
A: "Do Nothing" because the wave energy from the waves travelling 10,000 km is too strong
B: Groynes in place to slow down the effect of "Long shore drift"
C: Yavarland- Rapid erosion occurs here so nothing can be done
There are two sediment cells on the Island. It is the direction that Long Shore Drift travels.
Long shore drift causes all of the sediment to travel around the Island, this is why there are large beaches around Sandown area but little beaches around Compton. All of the sediment ends up sinking down a trough (shown by the blue circle)
Planting vegetation - make the cliff more stable
Beach nourishment - pump sand onto the beach, having dredged it from under the sea, to make a
nice big sandy beach. Has to be maintained as LSD moves the sediment down the coast all the
Offshore breakwaters - force the waves to break before they reach the beach.
In cliff drainage to prevent saturation.
Managed Retreat - people and activities are gradually moved back from the vulnerable areas of
Cliff Regrading - making the cliff face longer, so that it is less steep
Actions at the coast
Curved sea wall- Sends wave energy backwards out to sea which hits the next incoming wave
+Lasts 40- 50 yrs
-Not effective against climate change= sea level rise
Rip rap- Breaks up energy of the wave
-Expensive- Granite from Norway
Tetra-pods- Breaks up energy of waves
+Link together= strong
+Interesting for tourism?
-Can break up and erode
-Can prevent acess to beach- Health and Safety
Groynes- Slows down LSD
+Builds up beach for tourism
+Beach = best protection
-Impact- down drift
-No protection to homes
Hard rock coasts such as The Needle's have characteristics of...
1)High, steep rugged cliffs
2) Bare cliff faces with no vegetation and little loose rock
3) A few boulders and rocks which have fallen from the cliff
4) A clear sea at the foot of the cliff
Soft rock coasts such as The Military Road, south of Scarborough have characteristics of...
1) high, less steep and less rugged cliffs
2) piles of mud and clay which have slipped down the face of the cliff
3) very few rocks, some sand and mud at the foot of the cliff
4) Brown sea at the foot of the cliff (colour dependant on material from the cliff)
Hard engineering methods include...
1) Sea wall- a long concrete barrier built at the base of the cliff offshore
2) Groynes- wooden, rock or concrete "fences" built across the beach, perpendicular to the coastline
3) Rip rap- Large boulders of resistant rock
4) Revetments- slatted wooden or concrete structures built at the base of a cliff
5) Off- Shore reefs - rock or concrete barriers built on the sea bed a short distance from the coastline
Soft engineering methods include...
1) Beach replenishment- adding sand taken from somewhere else, often offshore
2) Managed retreat- people and activities are gradually moved back from the vulnerable areas of the coast
3) Cliff regrading- making the cliff face longer, so that it is less steep
Benefits of Sea Walls include...
1) protects base of cliff from erosion as it is made from resistant concrete
2) Land and Buildings behind it are protected
3) if it is "recurved" it can reflect wave energy
Costs of Sea Walls include...
2) High cost of maintenance
3) restricts access to the beach and can cause visual pollution
Benefits of Groynes...
1) prevent movement of beach material along the coast by Long shore drift
2) Enables beaches to build up and become an attraction for tourists
Costs of Groynes include...
1) Do not last very long
2) cause visual pollution
3) Sand is prevented from moving along the coast, causing other areas to lose their beach
Benefits of Rip rap include...
1) absorb wave energy
2) protect weak cliffs behind
3 Look relatively natural
Costs of Rip rap include...
2) let some wave energy
3) restrict access for the young and the elderly
Benefits of Revetments include...
1) absorb and spread wave energy through slats
2) do not interfere with long shore drift
Costs of revetments inlcude...
1) regular maintenance is needed
Benefits of Off-shore reefs include...
1) waves break on the barrier before reaching the coast
2) significantly reduce wave energy and allow a wide beach to develop
Costs of Off-shore reefs include...
2) can interfere with boats
Benefits of Beach replenishment
1) looks natural
2) provides a beach for tourists
3) beach absorbs wave energy, protecting the land and buildings behind
Costs of Beach replenishment
1) sea continues eroding it away, so it has to be replaced every few years
Benefits of Managed retreat...
1) Natural processes are allowed to happen
Costs of managed retreat...
1) compensation has to be paid
2) disruption caused to people's lives and businesses
Benefits of Cliff regrading
1) angle of cliff is reduced, making mass movement less likely
Costs of cliff regrading...
1) other methods need to be used at the base of the cliff to stop it being steepened again by erosion
2) properties on the cliff may have to be demolished
The force of the waves hitting the cliffs often forcing pockets of air into cracks, splitting them apart
Caused by the waves picking up stones and hurling them at the cliffs, wearing them away
Any material carried by the waves will become smaller and rounder over time as it collides with other material
Acids in sea water dissolve some soft rock types such as chalk or limestone,
Hard and soft rocks run parallel to the coast. Entrance to the cove is narrow where hard rock needs to be eroded, the cove widens where the softer rocks can be eroded more easily
Soft rock erodes quicker than hard rock. This causes the hard rock to stick out as a headland and for the soft rock to become a bay
Management at the Military Road
'Do nothing' approach=Rapid erosion
'Do nothing' approach=Rapid erosion
Why is there a do nothing approach at the Military Road?
Few buildings, mainly farmland=low value, the tourism industry can be relocated in land, the waves are also very powerful so would be very costly to protect. The eroded material can protect other, more valuable areas of coastline like Ventnor.
Management in Ventnor
Hard management (sea wall, rip-rap) =Little erosion
Why is there hard management in Ventnor?
It is densely populated so the land is of high value and it would be almost impossible to relocate people further inland.
Cliff retreat - Cliff foot erosion
Weathering - Cliff face
The movement of material along a coastline in a zig-zag fashion due to prevailing winds.
How are sand spits formed?
When there is a bend in the coastline, LSD carries the sand beyond the bend so it builds up as a sand spit.
Factors that affect coastlines
Rock type - Hard or Soft
Number of joints and faults
60 Km of coastline in Yorkshire
Low cliffs made of Boulder clay
Most erosion during storms
Dozens of villages lost
Two rock groynes and a 500m revetment were built in 1991. They cost £2million and were built to protect the village and the B1242 coastal road. Increased erosion to the South; Cowden farm is at risk of falling into the sea