Unit 2.2 Coastal Landscapes

Waves form from a transfer of energy from the wind. This causes friction with the surface of the sea, and the water begins to move in a circular motion. The amount of energy gained depends on:

• Wind speed
• Length of time the wind has been blowing for
• Distance of open water over which the wind blows (fetch)

Destructive Waves

• Created in storm conditions. They occur when wave energy is high and the wave has travelled over a long fetch.
• They tend to erode the coast.
• They have a stronger backwash than swash.
• They have a short wavelength and are high and steep.

Constructive Waves

• Created in calm weather and are less powerful than destructive waves.
• They break on the shore and deposit material, building up beaches.
• They have a swash that is stronger than the backwash.
• They have a long wavelength and are low in height.

Coastal erosion: The wearing away of the land by the sea

Hydraulic action: The pressure of water being thrown against the cliff by waves. The water gets into the cracks causing air compression to put pressure on the rock, making pieces of rock break off.

Abrasion: Sand and pebbles carried within the waves are thrown against the cliff face with considerable force. These particles break off more rocks which in turn also hit against the cliff. 

Solution: A chemical reaction between certain rock types dissolved by salt and other acids in the seawater. Particularly evident on limestone and chalk cliffs where water is milky 

Attrition: A process that involves the wearing away of the rocks which are in the sea. Boulders in the sea hit away at each other to create rounded sand and pebbles

Weathering: The breaking up of rock, but they don't move

Physical: Involves the breakdown of rocks and solids, torn apart by physical force, through direct contact with heat, water ice and pressure

• Freeze-Thaw: Water gets into cracks and expands as it turns to ice when temperatures fall. This expansion puts pressure on the rock around it causing fragments of rock to break off.

Chemical: Breaking down the bonds holding the rocks together, causing them to fall apart, forming smaller and smaller pieces.

• Rainwater contains weak acids that react with certain rock types. Carbonates in limestone are dissolved by weak acids causing the rock to break up or disintegrate.

Biological: Caused by living organisms, most often plant roots or burrowing animals.

• Rain causes seedlings, that fall in cracks, to grow. Roots force their ways into to cracks and break up the rock as they grow. Burrowing animal are responsible for the further break-up.

Mass Movement: when material moves down a slope due to the pull of gravity

Soil Creep: The slowest downhill movement. Gravity pulls water in soil downhill. Soil particles move with water. Heavy rainfall causes faster soil creep. The slope appears to have ripples known as terracettes.

Slumping: This is a large area of land moving down a slope. It is common on clay cliffs as the dry weather makes clay contract and crack. Therefore rainwater gets into the cracks and the soil becomes saturated. Due to the pull of gravity the large piece of weakened rock is pulled down the cliff face. It is said to have slipped on the slip plane of saturated rock.

• The erosion of a cliff is greatest at its base where large waves break. Hydraulic action and abrasion constantly undercut the foot of the cliff forming a wave-cut notch.

• The notch continues to get larger as the undercutting continues. Eventually, the overhang becomes so heavy and unstable that it collapses downwards due to to the pull of gravity.

• This process continues over time and the cliff gradually retreats inland and becomes steeper.

• As the cliff retreats, a gently sloping rocky platform is left at the base, this is known as a wave-cut platform which is exposed at low tide. The platform will also contain boulders which have fallen from the cliff.

• They form on coastlines where rocks of varying resistance lie at right angles (perpendicular) to the sea.

• Hard rock, e.g. chalk, is more resistant to erosion so forms headlands left sticking out to the sea.

• Softer rock, e.g. clay, is eroded at a quicker rate to form bays, in between two headlands. Deposition in the sheltered bay creates a beach.

• Erosion eventually becomes greater on the headlands because the bays have retreated and the headlands are more exposed.

• These are formed in headlands that have a fault. Wave refraction causes waves to attack the side of the headland and hydraulic action exploits the fault.

• In time the fault will widen to become a cave, through hydraulic action and abrasion.

• The cave becomes eroded through, creating an arch. If two caves form back to back this can also create an arch.

• The roof of the arch will eventually collapse due to the force of gravity, leaving a stack that is no longer attached to the headland.

• Continued erosion and weathering will lead to the formation of a stump, as the stack collapses into the sea.

• This is an ongoing process along the headland. There can be many caves, arches, stack and stumps at once.

This is the process where waves transport eroded material (sediment) along the coastline by the action of breaking waves. It is deposited further down the coast.

• Swash goes up the beach at the same angle as the wind
• Backwash moves straight down the beach at right angles to the beach due to the pull of gravity
• Sediment is moved in the overall direction of the prevailing wind

Material is deposited along the beach when water loses energy e,g:

• Seawater gets shallow
• A river flows into sea
• A headland or groyne juts out to sea

• Found on straight coastlines where longshore drift is happening

• Found in bays where the sea is shallower so the waves lose their energy and deposit what they are carrying

• Made up of sand and pebbles

• Formed by constructive waves

• A spit is an accumulation of sand with one end attached to the land and the other reaching out across an estuary or into the sea.

• They are formed where large amounts of sediment are transported by longshore drift and where the coastline suddenly changes direction to leave a sheltered, shallow area of water.

• Due to an increase in friction more deposition occurs in the water sheltered by the headland and the spit slowly builds up to sea level and extends in length.

• When the wind changes direction it causes waves to alter their direction and this may result in some material at the end of the spit being forced inland to form curved end.

• A salt marsh often develops behind the spit and the spit cannot grow across an estuary as the river current carries material out to sea.

Bar: If a spit joins one part of the mainland to another, e.g. two headlands, it's called a bar. This is only possible if there is no river entering the sea because rivers wash sediment away. Bars straighten coastlines

e.g. Slapton ley, Devon

Tombolo: When a spit joins the mainland to an island.

e.g. Chesil Beach

Sub-Ariel Processes:breaking up of rock through processes of weathering and the impact of wind and rain

• 3 Types of Weathering

• 4 Types of Erosion

• 2 Types of Sudden Mass Movement

-Slumping

-Rock falls

• 2 Types of Slow Mass Movement

-Soil Creep

-Flows: Very fine loose material becomes saturated with water and just flows down a slope e.g. mud flow

Geology: the rock type and is often the most important feature of the coast. Rocks range from hard to soft rock

• Speeds up? - Erodes more quickly. Lower cliffs, shallower inclines (less steep). Features like beaches. e.g boulder clay cliffs, Holderness Coast
• Slows down? - Erodes more slowly. Tall and verticle cliffs. Features like arches and stacks. e.g granite cliffs, West Cornwall

Fetch: The distance of open water over which wind blows over

• Larger fetch = bigger destructive waves, more energy to erode, increasing coastal erosion
• Shorter fetch = smaller less destructive waves, less energy to erode, decreasing coastal erosion

Coastal Management: Coasts protected by hard or soft engineering

• Doing nothing as it's not worth the money. Does not reduce coastal erosion rate
• Using, for example, a sea wall which absorbs wave energy to reduce coastal erosion rate

The cliffs of Happisburgh are soft as there is sand on top and clay below. They are therefore worn away easily. Coastal defences were installed in 1958, reducing erosion to 50cm per year, but council stopped repairs in 1995.

Effects on People:

• 25 properties and 1 business have been swept away
• Houses decreased in value from £80,000 to £1
• Government refuses to protect it as it is not cost effective

Effects on Environment:

• Animal habitats can be lost to the sea

Forecasting

• Met office predicts the likelihood of a flood. Info gets to householders through weather forecasts and news broadcasts on the TV. It is also on their website.
• Environment Agency monitors sea conditions 24/7. Info is provided on a 24-hour flood hotline and their website

Building Design

• In Bangladesh, one/two storey buildings must have external staircases to the roof.
• Houses along the coast of malibu are built on stilts to protect them from storm tides

Planning: Many countries have planned for coastal flooding by protecting themselves

• The Thames flood barrier was completed in 1982 to protect the London area against coastal flooding
• In Bangladesh, the Coastal Embankment project has led to the building of 12 sea facing walls and 500 flood shelters

Education: countries are educating their citizens about what to do if a flood occurs

• In Bangladesh, many coastal areas have flood warning systems
• In Kings Lyn in Norfolk people are employed to go house to house to warn people and help them prepare

Revetments - absorbs wave energy through slatted wooden structures built at the base of a cliff

• Cheap compared to other techniques. Effective for many years. 
• Can make beach inaccessible to tourists. Requires regular maintenance.

Riprap - large rocks placed in front of the cliff dissipates wave energy

• Effective for many years. Can be very cheap
• Unattractive. Not effective in stormy conditions

Recurved Seawalls - walls usually made of concrete; modern ones have recurved face which reflects wave energy

• Very visible making the resident feel safe. Effective for many years
• Expensive to build. Ugly - puts tourists off.

Groynes - Usually pieces of wood stretching from coastline to sea, preventing LSD as sand builds up on one side of the groyne

• Keeps beach in place for the tourist industry. Effective for many years.
• Disrupts natural processes working on the beach like LSD. Difficult to walk along beach.

Gabions - Wire cages filled with stone absorb wave energy

• Cheaper than other defences, but still reduces erosion.
• Wires cages can break, need to tied down securely. Not comparatively effective.

Offshore reefs - Enormous concrete blocks and natural boulders sunk offshore to alter wave direction and to dissipate the energy of waves and tides.

• Allows build up of sand, due to wave energy reduction. Wave break further offshore, reducing their erosive power
• Difficult to install. May be removed by heavy storms

Beach Replenishment - Placing of sand and pebbles on a beach. Beach is a natural defence that dissipates wave energy

• Looks natural. Cheap. Provides beach for tourists.
• May affect plant/animal life in the area. Requires constant maintenance as it all can be washed away very quickly, as little as one year.

Cliff Regrading - Cliff is cut back and given a new gentle slope to stop slumping.

• Very natural, encourages wildlife in the area. May be covered in ecomatting to encourage vegetation growth
• Needs other defences at cliff foot. Some homes on the cliff may have to be demolished.

Managed Retreat - Allowing sea to gradually flood land and erode cliffs

• Creates new habitats for plants and birds. Cheap.
• Upsetting for landowners who lose land. Difficult to estimate the extent of sea movement, especially with rising sea levels

1997

• Groynes built to stop longshore drift movement from south to north
• Cliff regraged and drainage channels installed to produce a gentle more stable slope.
• Slope planted with gorse and nettles to stop people climbing on the cliff
• Seawall built to protect the soft London clay at the bottom of the cliff

1998

• 300 tonnes of Leicester granite placed around the Tower breakwater

1999

• Beach replenished with sand and gravel from Harwich Harbour