COASTS - Physical Landscapes of the UK

Coast

Coast

is a narrow contact zone between land and sea

Coastline

is an ever changing boundary zone between the land and marine/sea environment

Constructive Wave

Waves are flat relative to length. Waves have a weak backwash and a strong swash. Waves are less frequent with between 6 and 8 breaking onto the shore every minute. These waves create a gradual beach angle. Often produce wide sandy beaches

Destructive waves

Waves are tall relative to length. Waves have a strong backwash and a weak swash.Waves are frequent with between 10 and 14 breaking onto the shore every minute. These waves create a steep beach angle. Often produces pebbly beaches.

Longshore Drift

The prevailing wind determines the direction of the waves. If the waves break onto the shore at a 45 degree angle to the coast, the swash pushes sediment up the beach and the backwash returns it back to the sea at right angles to the coast, due to the force of gravity. Over time this zigzag movement carries sediment along the beach.

Erosion

The wearing away of the earth’s surface by the action of wind or water

Transportation

The movement of material from one place to another (varies from fine silt to large rocks)

Deposition

When waves drop and leave behind the load (sediment/rocks) they were carrying).Deposition takes place at low energy sheltered bays where constructive waves prominent

Hydraulic Action

Destructive waves hit the base of cliffs.This causes water to enter cracks, joints, faults at high speeds. The air in these cracks are compressed and as the wave retreats a mini explosion takes place as pressure is released. This repeated action causes the cracks to widen and the cliff to become weaker

Abrasion (Corrasion)

Waves have energy to carry material and at times large rocks. The waves throw the material at the cliff face scratching and scraping the surface.

Atrrition

Involves the grinding down of load particles. During transport rocks and pebbles collide and over time they become smaller and smaller due to the wearing away of jagged edges creating smooth round pebbles.

Traction

Traction moves the biggest pieces of material (rocks, boulders) along the sea bed. They never leave the sea bed. The force of the water pushes and rolls the boulders.

Saltation

Load is bounced along the sea bed, e.g. small pieces of shingle or large sand grains. Currents cannot keep the larger and heavier sediment afloat for long periods.

Suspension

Small particles are carried in water, e.g. silts and clay, which can make the water look cloudy. Currents pick up large amounts of sediment in suspension during a storm, when strong winds generate high energy waves.

Solution

Minerals are dissolved in sea water and carried in solution. The load is not visible.

Weathering

- the breakdown of rocks over time. This process produces material which creates coastal land forms or the sediment taken away through transportation. 

Biological Weathering

the breakdown of rocks due to the actions of plants, bacteria and animals

Chemical Weathering

The breakdown of rocks through chemical reactions. The most common type of chemical weathering is carbonation, where acid rain reacts with calcium carbonate in rocks to form a chemical compound which can then be easily dissolved. 

Mechanical Weathering

the breakdown of rocks due to exertion of physical forces without any chemical changes taking place.

Mass Movement: Landslides

Water between sheets of rock (called bedding planes) and the rock face reduces friction and allows large chunks of rock to slide down the cliff.

Mass Movement: Rock Fall

Occur on sloped cliffs when the rock becomes exposed to mechanical weathering 

Mass Movement: Rotational Slip

Also known as slumps, soil and rock fragments become saturated with water. However, instead of sprawling down the hill like a mud flow, chunks of rock and soil slip, creating stepped ‘heads’ down the cliff face.

Discordant Coastline

Coastlines where the geology alternates between strata (bands) of hard rock and soft rock.

Concordant Coastline

has the same type of rock along its length. Concordant coastlines tend to have fewer bays and headlands.

Headland

A cliff that juts out into the sea so it is surrounded by water on three sides.Composed of hard rock

Bay

A crescent-shaped indentation in the coastline found between two headlands. Usually has a beach composed of sand or shingle. Bays are sheltered by the headlands and become low energy environments where deposition takes place.

formation of a stump in a headland

-A large crack is enlarged by hydraulic action.

-The crack grows into a notch then a cave as destructive waves converge on the headland continue to erode it.

- Over time the cave becomes larger. Wave refraction draws waves to all sides of the headland so caves may form back to back.

-Sea breaks through the back of the caves forming an arch. The base of the arch is widened as the notches form.

-Weathering such as freeze-thaw continues to weaken the top of the arch, making it less stable.

-The top of the arch eventually collapses. This leaves a stack.Notches form at the base of the stack which eventually makes it unstable

-The stack eventually topples into the sea leaving only its base, the stump. It is only visible at low tideForma

Wave Cut Platform

An area of bedrock visible at the base of some cliffs. It is generally only visible at low tide.

Formation of Wave cut Platform

-Weak lines in the cliff are eroded by abrasion and hydraulic action. A notch at the base of the cliff is formed and the cliff overhangs.

-The sea erodes the cliff further and further.As the cliff becomes unstable materials fall off into the sea.The very base of the cliff is below the sea and is not eroded. A platform is left.

-As the cliff collapses over and over again it causes the cliff to retreat. Leaving a Wave Cut Platform.

Beaches

Formed by constructive waves depositing material on the beach

Sand Beaches

flat and wide, sand particles are small and backwash can move them back down the beach forming a gentle slope

Shingle Beaches

steep and narrow, shingle articles are large and backwash cannot move them back down the beach therefore building up a steep slope

Sand Dunes

large heaps of sand that form on the dry backshore of a sand beach

Formation of a Sand Dune

-The onshore wind carries/transports the sand via saltation and suspension up the beach

-Heavier sand particles settle against an obstacle and lighter particles are transported and settle behind the obstacle

-Sand continues to build up around the obstacle on the windward side causing the sand dune to grow in size and form a crest

-Height builds up until the structure becomes unstable

-Sand then slips down the leeward slope

-A sand dune becomes an obstacle, so more dunes may move in front of it

Spit

a stretch of sand or shingle extending from the mainland out to sea.

Formation of a Spit

They develop where there is a sudden change in the shape of the coastline such as at a headland. When the shape of the coastline changes, longshore drift continues to transport material in the same direction rather than following the coastline. This transports the material out to sea. As the strength of the drift weakens away from the coastline, the sediment is deposited.The deposition of sediment forms a spit but its shape changes as a result of wave refraction.

Refraction around the end of a spit curves it into a "hook" forming a re-curved spit.As the area behind a spit is sheltered from waves and the wind, it provides the perfect environment for salt marshes to develop

Jurassic Coastline

is situated on the Southern coast of England and stretches between Bournemouth to Exmouth in East Devon. The Jurassic Coastline has many different features due to its varied geology. It is a discordant coastline made up of a variety of bands of chalk, clay and limestone.

Old Harry

an example of a stack, a pillar of rock which was once part of a headland,exists due to the headland being made up of chalk compared to the bands of softer clay and sand either side. Erosional processes such as hydraulic action and abrasion erode the coastline but due to alternating bands of soft and hard rock, it forms a headland.Old Harry is then part of an eroded headland and stands as a stack out at sea. This stack would have once been attached to the headland however processes of erosion and weathering and have separated the pillar from the headland.

Durdle Door

is a natural limestone arch also found along the Jurassic coastline. It is made up of hard resistant limestone again between two softer layers of clay. The soft rock is eroded by the processes of hydraulic action and abrasion, producing a limestone headland. This headland is continuously eroded by the sea and a notch/fault in the headland will gradually become a cave. Over time the back of the cave will be broken through due to continued erosion therefore producing an arch

Swanage Bay

is a beautiful sheltered beach formed of clay. This clay is situated next to a limestone headland at Purbeck and a chalk headland to the east. The softer clay is eroded faster than the headlands meaning the land retreats forming a bay. A beach has built up at Swanage Bay due to deposition via waves.

Hard Engineering

Structures that have been built to alter or to defend the environment. Include anything designed to prevent cliff erosion along the shore or at the foot of a cliff. Man-made.

Soft Engineering

Those that adapt and encourage natural processes to take place. Natural

Groynes(Hard Engineering)

are wooden or stone barriers constructed at right angles to the beach to retain material.Material is trapped between these groynes and cannot be transported away by longshore drift. Groynes Encourage a wide beach on the updrift side, which helps absorb energy from waves, reducing the rate of cliff erosion. They are particularly effective when used in conjunction with beach recycling.

Beach re-profiling(Soft Engineering)

This is the artificial re-shaping of the beach using existing beach material. After winter storms,bulldozers move shingle back up the beach. A wide beach means fewer waves reach the back of the beach and also the waves energy is absorbed and dissipated by the beach, which reduces the rate of erosion.

Gabions(Hard Engineering)

This is where rocks and boulders are encased in wired mesh and placed at the back of the beach. They absorb and dissipate the energy from waves

Sand Dune Regeneration(Soft Engineering)

The artificial creation of new sand dunes or the restoration of existing dunes results in a physical barrier between the sea and the land, absorbing wave energy.

Beach Recharge(Soft Engineering)

For the replacement of lost sediment through longshore drift, where shingles are dredged from the seabed and pumped onto the beach.

Rock Armour(Hard Engineering)

These are often large boulders of hard rock placed along the base of a cliff to absorb energy from waves as water enters gaps between the boulders.

Sea Wall(Hard Engineering)

Usually built along the front of the cliffs/back of the beach, often to protect settlements. They are often recurved which reduces overtopping and means waves are reflected back on themselves. This impeded the next wave and reduces its energy and thus its erosive power.

Advantages of Sea Wall

• A sea wall gives people a sense if security. It often has a promenade on top of it, which can double up as a cycle route. Steps at the base of a wall act as seating areas for beach users

• If well maintained, sea walls can last for up to 50 years.

• Sea walls do not impede the movement of sediment downdrift, so they do not disadvantage other areas.

Disadvantages of Sea Wall

• From the beach, a wall of concrete is ugly to look at. Sea walls can destroy habitats.

• At about £5000 per linear metre, sea walls are expensive to build. Repairs are also expensive. Reflected waves scour the beach in front of a sea wall and this undermines its foundations. If damage is not repaired quickly, the result may be devastating.

• They restrict people's access to the beach, and if waves break over the sea wall, coastal flooding may occur.

Advantages of Groynes

• Rock groynes can have concrete crests for people to walk along to reach a viewing or fishing point. They can act as windbreaks.

• At £5000 each, groynes are relatively cheap and if well-maintained can last up to 40 years. A larger beach with more space for activities attracts more tourists, which boost the local economy.

Disadvantages of Groynes

• By trapping sediment, groynes restrict the supply of sediment downdrift. The problem is merely passed on to incur more cost elsewhere. Groynes are ineffective in stormy conditions and regular maintaining so they do not rot

• Groynes may be considered unattractive, especially degraded ones.

• Groynes are barriers, which impede walking along a beach. They are also dangerous as they have deep water on one side and shallow water on the other. This is a particular hazard to children who find it hard to resist climbing on them. Groynes may also be a danger to wind surfers, who may collide with them

Advantages of Rock Armour

• It is relatively cheap, costing £1000-£3000 a metre

• The structure is quick and easy to build. It can be built in weeks rather than the months it takes to build a sea wall. If well maintained the rock armour lasts a very long time.

• It is versatile and can be placed in front of a sea wall to lengthen its lifespan or used to stabilise slopes on sand dunes

Disadvantages of Rock Armour

• Rock armour is ugly and often covers vast areas of a beach. Driftwood and litter become trapped in the structure and imported rocks do not blend in with the local geology

• Highly resistant rocks from Norway and Sweden are often used in preference to rocks from local quarries. This may cause resentment and inflate the cost considerably. Also, heavy storm waves will move rocks and so armour needs regular maintaining.

• Rock armour makes access to the beach difficult as people have to clamber over it or make long detours. People may have accidents when clambering over it as rock may be unstable and if regularly covered by the tide they may collect slippery seaweed

advantages of Gabions

• They blend in better than other hard engineering methods, especially when sand is blown into them or when they are covered by vegetation.

• At £110 a metre they are relatively cheap and easy to construct. Gabions are often constructed on site using local pebbles. This makes them much cheaper than sea walls, rock armour or groynes. It also makes them ideal as a quick-fix solution, they are good value for money as they may last 20-25 years.

Disadvantages of gabions

• The use of gabions is restricted to sandy beaches as shingle hurled at them would quickly degrade them. Gabions are easily destroyed, so regular maintenance is needed. Repair of embedded, vegetation-covered gabions can be expensive

• Damaged gabions are unsightly and sea birds may damage their feet in them.

• In a damaged state, gabions are dangerous. People may trip over them or cut themselves on the broken steel wire mesh.

Advantages of Beach Nourishment

• Wider beaches protect expensive properties and reduce sea wall maintenance costs. A broader beach may attract more tourists.

• A nourished beach is natural and blends in with the environment.

• A wider beach has more room beach users. People living along the seafront are more protected from coastal flooding.

Disadvantages of Beach Nourishment

• During re-nourishment, access to the beach is restricted for several weeks. Beach recycling may causes resentment from residents living close to the donor area.

• Although cheaper than hard engineering, this has high overheads as it costs around £300,000 to hire a dredger

Advantages of Beach re-profiling

• Residents feel safer with a built up beach.

• By reprofiling ecosystems behind the beach are protected and the beach still looks relatively natural.

Disadvantages of Beach re-profiling

• A steep, high-crested beach may look unnatural and uninviting to tourists.

• Bulldozers may restrict access to the beach, especially in winter.

• The cost of the damage and the cost of repairing a shingle ridge if it is breached is likely to be higher much higher than the cost of regular reprofiling.

• Major reprofiling costs can be expensive. 

Advantages of Sand Dune Regeneration

• Sand dune regeneration can help maintain a habitat for rare species.

• Small planting projects often use volunteer labour and local grass for transplants so costs are minimal.

• Sand dunes protect land uses behind them. Once established, they are popular as picnic and walking areas

Disadvantages of Sand Dune Regeneration

• While becoming established, regenerated sand dunes are fenced off and signs tell people to keep out. This may deter tourists.

• Dune regeneration has to be checked twice a year and have fertilisers applied.

• Sand dunes are a dynamic environment. Once regenerated there is no guarantee that they will be stable. The grass may be damaged by storms. It takes 2-3 years to become established and spread.

• Expensive systems have to be put in place to prevent planted areas from trampling in popular areas. E.g. board walks, fire warnings and fire beaters.