Coasts GCSE AQA

Includes Lyme Regis case study

Coast

A narrow contact zone between land and sea and has an ever changing boundary between the land and the marine/sea environment.

Why are coastlines important in the UK?

• Home to over 30 million people

• Brings money through tourism

• Employment in the fishing industry

• Imports and exports by sea

Relationship between wind and wave

Generated by wind blowing over the sea. The stronger the wind, the greater the friction on the surface of the sea and therefore the bigger the wave.

Swash

When a wave breaks, water rushes up the beach. On most beaches, it approaches at an angle, determined by the wind direction.

Backwash

The water runs back down the beach under the force of gravity at a 90 degree angle.

What happens when waves reach shallower water?

In open water, the water in the wave is in a circular orbit, but as friction slows down the base of the wave, the wave becomes more elliptical in movement, and the top of the wave moves faster, eventually beginning to break, as water from the previous wave returns as backwash. The water then rushes up the beach as swash.

Factors affecting the size of waves

1. Strength of wind

2. Length of time the wind has been blowing

3. The fetch

Fetch

The distance that the wave has travelled

Constructive waves

Low wave height, long wave length, powerful swash that pushes material up the beach, weak backwash, weaker winds, low energy, short fetch, 6-9 wave frequency per minute, deposition greater

Destructive waves

High wave height, short wave length, weak swash, powerful backwash, high energy, strong winds, long fetch, erosion greater, 11-15 wave frequency per minute

Weathering

The disintegration or decay of rocks in their original location on the Earth’s surface, often resulting in angular fragments.

Chemical weathering

Weak acids in rainwater react with certain rock types, like limestone, and causes them to break away

Biological weathering

When seeds fall into cracks in the cliff, the roots expand and break away the cliff

Freeze-thaw weathering

Water gets into cracks as rain and as overnight temperatures drop, the water turns to ice and expands

Slump

Soft rock cliffs become saturated with rain, this makes them heavy. With undercutting by the sea, they will slump.

Slide

Top layer of rock becomes saturated by rain; heavy and under gravity, it may break off and slide over the layer of rock below.

Flow

Fine loose material becomes saturated and flows down the slope

Fall

Freeze-thaw weathering shatters rocks from the cliff, the rock falls under gravity to the cliff base and they form talus/scree slopes.

Wave cut platform

An area of bedrock visible at the base of some cliffs, generally only visible at low tide. They occur in resistant rocks often within a headland.

Formation of a wave cut platform

Hydraulic action erodes the cliff between the low & high tide marks, and a wave cut notch is formed. Biological weathering will then weaken the top of the cliff and the cliff above the notch collapses, leaving behind a wave cut platform.

Formation of headlands and bays

Waves attack the coastline, and the less resistant rock is eroded by the sea, forming a bay. The resistant rock is left sticking out on either side, forming headlands. The shallower water in the bay will lead to deposition and the formation of a beach.

Hydraulic action

Waves force water into cracks in a cliff, and air is trapped and expands, causing the cracks to get bigger

Abrasion

Sediment carried by the wave is thrown at the cliff, hitting and scraping it, causing further cracks or rock to fall away

Attrition

Sediment carried by the wave knocks into eachother, making it rounder and smoother

Solution

The seawater reacts with some rocks, dissolving the rock into it. The cliffs that react are usually limestone or chalk.

Discordant coastline

Bands of rock are perpendicular to the sea, meaning as you walk along the coast, you will find different bands of rock.

Concordant coastline

Bands of rock are parallel to the sea, meaning as you walk along the coast, you will find the same bands of rock.

Sand beaches

Flat, wide, sand particles are small so backwash can move them back down, causing a gentle slope

Shingle beach

Steep, narrow, shingle articles are large so backwash cannot move them back down, causing a steep slope

What does a sand dune need to form?

A large, flat beach, with a large supply of sand and an onshore wind to move the sand to the back, as well as an obstacle of sorts, eg. driftwood

Formation of a sand dune

1. Onshore wind carries/transports the sand via saltation and suspension up the beach

2. Heavier particles settle against an obstacle and lighter particles settle behind it

3. Sand continues to build up around the obstacle on the windward side

4. Height builds until it becomes unstable

5. Sand slips down the leeward slope

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

Saltation

Hopping/bouncing motion of particles too heavy to be suspended

Suspension

Particles carried within the water

Traction

Large pebbles moved along the seabed

Longshore drift

The movement of sediment along the beach

Formation of a cave

Hydraulic action causes the widening of cracks in the cliff, and along with abrasion, it widens the cracks so the open up to form a cave

Formation of an arch

Hydraulic action and abrasion continues to erode the cave until it breaks through the back wall, forming an arch

Formation of a stack

Hydraulic action and abrasion erodes the bottom of an arch and weathering weakens the top, eventually causing it to collapse and leave a stack. The cliff behind then retreats.

Formation of a stump

Continued erosion at the bottom of the stack will weaken it and cause it to collapse, forming a stump

Wave refraction

As waves approach a headland, they begin to slow down due to shallower water around the headland and the waves energy converges on the headland. However, the waves that remain in deeper water continue to move faster towards the bay as they are unaffected by friction. The bays become sheltered from waves easily and so deposition takes place.

Formation of a spit

Longshore drift occurs in the direction of the prevailing wind, and at the end of the beach the sediment is deposited, and as deposition continues, the beach grows out past the headland, forming a spit. If the wind direction changes, it changes the direction of the longshore drift, forming a hook on the spit. The river estuary will then prevent the spit from getting longer, and a salt marsh forms behind the spit.

Formation of a bar

A spit starts to grow across a bay, eventually joining the other side, and the old bay becomes a lagoon.

Formation of a tombolo

A spit begins to grow until it joins an island, forming a tombolo

Hard engineering

Structures that have been built to alter or to defend the environment. Man made.

Soft engineering

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

Groynes

Prevent longshore drift. Wooden or stone barriers constructed at right angles to the beach to retain material.

Gabions

Prevent erosion. Where rocks + boulders are encased in wired metal mesh and placed at the back of the beach, which absorb and dissipate the energy from waves.

Sea wall

Prevent erosion. Often curved and built to protect settlements, they reflect the waves back on themselves.

Rock armour

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

Beach nourishment/recharge

Prevents erosion, is the replacement of lost sediment through longshore drift. Shingle is dredged from the seabed and pumped onto the beach. It is soft engineering.

Beach reprofiling

Prevents erosion. Artificial re-shaping of a beach, where shingle is moved back up the beach with bulldozers to absorb and dissipate the wave energy. Soft engineering.

Sand dune regeneration

Prevents erosion, it is the artificial creation of new sand dunes, or the restoration of existing dunes, creating a physical barrier between the sea and sand, absorbing wave energy. Soft engineering.

Lyme Regis management phase 1

It took place in the 1990s and cost £10 million. A sea wall and promenade was built and cliff nailing stabilised the cliffs. It successfully protected the coast and stabilised key areas, as well as improving infrastructure, however, emergency cliff nailing cost an extra £1.4 million and some residents felt that engineering interfered with natural coastal processes, having an impact on the environment.

Lyme Regis management phase 2

Occured in 2005-2007, it cost £22 million and it created more of the sea wall and promenade, as well as the creation of a wide shingle and a sand beach, and the extension of rock armour at the Cobb. It enhanced coastal protection, boosted tourism and increased shelter for the harbour, however tourism brought issues like traffic and litter, and some people argued that the sea walls looked unnatural and spoiled the natural beauty.

Lyme Regis management phase 3

It was not undertaken, since its cost outweighed its benefits

Lyme Regis management phase 4

It occured in 2013-2015, and cost £20 million. It built a 390m sea wall in front of the old one, and extensive work stabilised the cliffs in order to protect 480 homes. However, it reduced fossil finds and there were concerns that interfering had caused increased erosion elsewhere, such as in Charmouth.