Coasts

What are the sections of the littoral zone?

Coast: land adjacent to the sea

Backshore: above high tide level

Foresore: between low and high tide

Nearshore: shallow water close to land

Offshore: open sea

How can coasts be classified?

Geology → rock type/structure

Sea level change → eustatic or isostatic

Tectonic activity → land rising/sinking

Waves → constructive/destructive

What are the features of rocky coastlines?

• High energy

• Destructive waves

• Exposed to strong winds

• Erosion dominant

• Headlands/wave-cut platforms formed

What are the features of coastal plains?

• Low energy

• Constructive waves

• Sheltered locations

• Deposition dominant

• Spits etc. formed

What is strata and deformation?

Strata: diferent layers of rock exposed in a cliff.

Deformation: tilting and folding caused by tectonic activity.

What are the two types of coastline caused by geological structure?

Concordant: rock runs parallel to the coast

Discordant: rock runs vertical to the coast

How are headlands and bays formed?

• Soft rock is eroded quicker, forming bays

• Hard rock is more resistant, forming headlands

• Headlands cause waves to refract, increasing erosion

What forms at concordant coastlines?

Dalmation coasts: valleys parallel to the coast that have flooded and formed islands.

Haff coasts: deposition produces unconsolidated structures parallel to the coastline.

What are dips?

The angle of rock strata.

What are joints, faults, fissures, and folds?

Joints: fractures in rock, which create fissures.

Faults: major fractures in rock caused by tectonic forces.

Fissures: smaller cracks in the rock.

Folds: bends in rock caused by tectonic compression, heavily jointed and fissured.

What is coastal recession?

How fast a coastline moves inland.

What are the three rock types?

Igneous → formed from solidified magma

Metamorphic → recrystallisation of sedimentary/igneous rocks

Sedimentary → compaction of deposited material

How fast do the rock types erode and examples?

Igneous → very slow, less than 0.1cm a year. Granite

Metamorphic → slow, less than 0.1 - 0.3cm a year. Slate

Sedimentary → moderate to fast, 0.5 - 10cm a year. Limestone

Glamorgan Heritage Coast

• South Wales

• 14 mile stretch of high-energy coastline

• Discordant coastline

• Sedimentary rock

• Has jointing, dips, faulting, and folding

• Has led to the formation of cliff profiles

How does vegetation stabilise salt marshes?

• Roots bind sediment together, preventing erosion.

• Reduce wind speed, preventing erosion.

• Provide a protective layer when submerged.

How does vegetation help form salt marshes?

• The tide brings in sediment, which settles on mudflats.

• Salt tolerate plants settle and stabilise.

• Halophytes slow tidal flow and trap more sediment..

• Surface becomes drier, allowing more plants to settle.

What is the succession of dunes?

Berm, embryo, yellow, grey, mature.

How do sand dunes form?

• Driftwood/litter trap sand at the berm.

• Vegetation starts to accumulate on the embryo.

• Dunes increase in size further inland due to wind.

• Vegetation and soil nutrients also increase.

How are sand dunes threatened?

• People walk/settle on dunes, pressure destroying vegetation.

• Sand becomes loose, causing a blowout.

How do mangroves help stabilise coastlines?

• Small trees that have adapted to groe in low-oxygen soil.

• Breaks the waves and prevent coastal erosion.

What is the importance of mangroves in Bangladesh?

• One million people rely on the mangrove forest.

• Mangroves have hit their salt limit and have begun to die off, leaving coastal villages vulnerable.

• Overfarming has begun to occur, causing degredation.

What is a wave caused by?

• Friction between the wind and water surface.

• This transfers energy and creates ripples, which build into waves.

What are the features of destructive waves?

• High energy

• Strong backwash, weak swash

• Tall wave height

• Shortt wavelength

• Low frequency

What are the features of constructive waves?

• Low energy

• Strong swash/weak backwash

• Shot wave height

• Long wavelength

• Low frequency

What are beach landforms?

Storm beaches: high energy deposition of coarse sediment during severe storms.

Berm ridges: shingle/gravel.

How do destructive waves alter beach morphology?

• Cause net movement of sediment up the beach

• Produce berms at high tide

• Sand remains in the foreshore and rocks are transferred higher up the beach

How to constructive waves alter beach morphology?

• Net transport of sediment down the beach

• Sediment is thrown foward by waves, forming a storm ridge above high tide.

How does coastal morphology change periodically?

Decadal → climate change alters seasons/weather.

Seasonal → destrucitve waves dominate in Winter.

Monthly → tide height varies over the lunar month.

What are the four types of coastal erosion?

Abrasion → when destructive waves scrape/throw rocks at the cliff face.

Attrition → when rocks collide with each other as they are moved by waves.

Hydraulic action → when pressure exerted from waves loosen rock.

Solution → seawater/saltspray reacts with rocks and dissolves them

What are erosional coastal landforms?

• Cave-arch-stack-stump sequence

• Wave cut notches/platforms

How are wave-cut platforms formed?

1. Hydraulic action and abrasion create a wave cut notch.

2. As erosion continues, the cliff continues retreating and forms an overhang.

3. The unsupported overhang collapses due to gravity and weathering.

4. Backwash transports material from the cliff base, leavung behind the platform.

How does the cave-arch-stack-stump formation occur?

• Joints in the clifface are susceptible to hydraulic action.

• Over time, these widen and a cave is formed.

• Erosion cuts through the cliff, forming an arch.

• The roof of the cave collapses due to gravity/lack of support.

• This leaves behind a stack, which once eroded becomes a stump.

What are the forms of sediment transportation?

Traction → sediment rolls along the seabed.

Saltation → sediment bounces along the seabed.

Suspension → sediment is carried by waves.

Solution → dissolved material is carried by waves.

What is longshore drift?

• Waves approach the beach at an angle, influenced by prevailing wind.

• Swash carries material up the beach at this angle.

• The backwash carries the material down the beach at 90°.

What is current?

The flow of water in a specific direction.

• Transports sediment.

• Surface currents are formed by wind.

• Thermohaline circulation: deepwater currents caused by density differences.

What are the depositional landforms?

• Spit

• Tombolo

• Bar

• Lagoon

• Cuspate forelands

What are spits and how are they formed?

Extended stretch of sand/shingle.

• Sediment is transported along the coastline by longshore drift.

• When the coastline changes direction, waves lose energy and sediment is deposited.

What are bars and tombolos and how are they formed?

Bars: spits that join together two headlands, leaving a lagoon.

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

What is a cuspate foreland and how is it formed?

A triangular feature extending from the shoreline.

Growth of two spits from opposing longshore drift directions.

What is a sediment cell?

A stretch of coastline bordered by two headlands, where sediment movement is contained.

What are the sources, transfers and sinks of the sediment cell?

Sources → where sediment is generated e.g. cliffs.

Transfer zones → where sediment is moved e.g. beaches.

Sinks → where deposition is dominant, and depositional landforms are created e.g. spits.

How many sediment cells is the English/Welsh coastline divided into?

11

Portland Bill to Selsey Bill

• High energy waves from the SouthWest lead to erosion.

• Prevaling winds from SW drive longshore drift.

• Chesil beach → one of the largest in the UK (20km).

• Cliff retreat at Purbeck → caused by storms and risng sea levels.

What are the three types of weathering?

• Mechanical: freeze-thaw/salt crystallisation

• Chemical: carbonation, hydrolysis, oxidation

• Biological: plant roots, rock boring

What are the two forms of mechanical weathering and how they occur?

Freeze-thaw

• Water expands when frozon, exerting a force within cracks/fissures

• Force cracks open and loosens rocks

Salt crystallisation

• Growth of salt crystals in cracks/pores exerts a breaking force

What are the three forms of chemical weathering and how they occur?

Carbonation

• Dissolution of limestone due to rainfall producing calcium carbonate

Hydrolysis

• Breakdown of minerals to form clay due to water and dissolved CO2

Oxidation

• The addition of oxygen to minerals, which increases volume

What are the two forms of biological weathering and how they occur?

Plant roots

• Grow in cracks and fissures, forcing them apart

Rock boring

• Clams and molluscs bore into the rock and potentially secrete chemicals that can dissolve rocks

What are the four types of mass movement?

• Rockfall

• Topple

• Rotational slide/slumping

• Flow

What is rockfall?

• Rapid form of mass movement

• Rock can be dislodged by weathering/hydraulic action

• Undercutting of wave-cut notches can lead to large falls and talus scree slopes at their base

What is topple?

• When rock strata has a steep seaward dip, undercutting quickly creates instability

• Blocks of material topple seawards

What is rotantional slide/slumping?

• Occurs on a curved failure surface

• Huge masses of material rotate slowly downslope

What is flow?

• Common in weak rocks e.g. clay/unconsolidated sands

• Material becomes saturated and lose their stability, flowing downslope

What landforms does mass movement create?

Rotational scarring → resultant of rotational slumping, curved, un-weathered, un-vegetated, the detatched material settles at the base of the cliff.

Talus scree slope → fan-shaped mound of material, composed of block-fall debris that has accumulated at the base.

Terraced cliff profile → cliff profile is stepped, resultant of lithology or rock fractures.

What is the difference between eusostatic and isostatic sea level changes?

Eusostatic: global change in the volume of water in ocean basins.

Isostatic: local change, height of land changes relative to water level.

What are eustatic changes caused by?

Global changes in the amount of ice as a result of:

Thermal expansion → water warms and takes up greater volume

Tectonics → magma rising lifts the crust and reduces ocean capacity

Ice ages → global sea level rose at the end of the ice age

What are isostatic changes caused by?

Localised changes caused by:

Post-glacial → ice sheets weigh ice down, causing the ice to rebound and lower sea level when melted.

Accretion → net deposition causes built up land within the sediment cell.

Tectonics → lava and ash increase land height

What is the difference bwtween emergent and submergent coastlines?

Emergent: created by a fall in sea level/rise in land.

Submergent: rise in sea level/fall of land.

What are emergent coastline landforms?

Raised beaches: beaches above high tide level

Fossil cliff: steep slope at the back of a raised beach

What are submergent coastline landforms?

Ria → flooded lower course of a river valley

Fjord → u-shaped valley carved out by a galcier and flooded.

What is the contemporary sea level?

• Rate of rise is 3.6mm anually.

• Sea level has steadily incresed since the industrial revolution.

• Prediction that 2100 sea levels will be 0.77m higher than modern day.

• 80% of the Maldives could be inhabitable by 2050.

What is coastal recession?

The retreat of a coastline inwards.

What human actions encourage coastal recession?

Dredging → the removal of sediment from the sea, which impacts the amount of sediment deposited.

Dams → trap river sediment behind the dam wall, starving the coast of sediment.

Coastal management → affects rate of erosion

What physical factors can influence coastal recession?

• Destructive waves

• Weak geology

• Structural cliff weaknesses

• Strong longshore drift

How has coastal management on the Holderness coast influenced recession?

• Groynes at Hornsea reduce longshore drift.

• Causes terminal groyne syndrome down the coast, such as in Mappleton.

Nile Delta

• Located in NE Africa, where the Nile enters the Mediterranean Sea.

• 240km wide.

• Area of intense farming and touism.

• Sea level rise (submergence) has encouraged erosion.

• Aswan dam has prevented normal flooding preventing deposition.

What are sub-aerial processes?

Weathering and mass movement

How do sub-aerial processes impact the Holderness coast?

Predominantly boulder clay leading to:

Wetting + drying → particles expand at high tide when wet, then shrink when dry, causes clay to crumble

Freeze-thaw → water enters fractures, expands due to Arctic maritime air masses, cause cliff weakening

Slumping → weathering leaves cracks in boulder clay, where water enters and causes the clay to become heavier and causing arotational slip.

How has coastal recession at the Holderness coast been managed?

Retreats 1-2 metres every year.

• Mappleton has 50 properties at risk to erosion, protected by rock groynes.

• Bridlington is being protected by a 4.7km sea wall.

• Spurn head is protected by groynes and rock armour.

What can coastal recession be influenced by short-/long-term?

Wind direction → erosion increases when winds blow onshore.

Fetch → when prevailing wind is congruent wth the largest fetch, there is a build up of destructive waves.

Tides → recession increases during high tide due to increased energy.

Seasons → storm events are more common in winter.

Weather → during depressions (low pressure) winds are stronger.

How has global sea level rise threatened the Maldives?

• 97% of inhabited islands in the maldives experience erosion.

• 80% of the islands will become inhabitable by 2050.

• Sustainable coastal management is overlooked in favour of protecting tourism.

• Mangroves for the Future are educating communites about the importance of mangrove defences.

• Global Environment Facility has provided grants to locals to help develop sustainable and oganic farming.

What factors increase flood risk?

High population → common in low-lying coasts due to tourism and fertile lands.

Vegetation removal → destabilises coastal sediment, 35% of mangroves have been lost since the 1950s.

Low-lying lands → more vulnerable to rising sea levels/storm surges.

Subsidence → (sinking of land) increased risk from urbanisation and agriculture.

What are storm surges?

Temporary rise in sea level caused by:

Depressions → areas of low pressure that bring rain, and increase sea level (inverse barometer effect).

Tropical cyclone → area of low pressure formed by warm rising from the ocean surface.

How does climate change increase flood risk?

Global sea level rise → a 50cm sea level rise would impact 800 million people globally, £120 billion UK infrastructure at risk of flooding.

Increased frequency/magnitude of storms → increasing ocean temperatures multiply the risk.

What are the costs of coastal recession for communities?

Economic → property/infrastructure loss

Social → rehabilitation and livelihood

Enironmental → coastal ecosystems lost

What are developing vs. developed countries more threatened by?

Developing → greater magnitude of deaths, injuries, and poorer quality infrastructure.

→ leads to less preperation/planning, poor emergency service response and lack of public education

Developed → higher economic losses due to higher value of property/infrastructure (quality of materials and technology)

Why are economic losses from erosion small?

• Occurs slowly, with a small number of properties affected over a long period

• At risk property loses value long before it is destroyed

• Areas of high population/economic cost are typically ptoyected by coastal defences.

How was Bangladesh vulnerable to and affected by Cyclone Sidr?

Vulnerable as:

• 50% of land is less than 8 metres above sea level

• Coastline is over 600km long

Afected by:

• 2007

• Storm surge reached up to 6m

• Over 3,000 deaths and 55,000 injuries

What are environmental refugees?

A person forced to move due to environmental changes

How many people are likely to be displaced by sea level rise by 2100?

630 million

How is the Seychelles vulnerable to global warming?

• 80% of people live and work on the coast

• Coral reefs act as erosion defences, but are being destroyed by global warming and coral bleaching

How many environmental refugeese are there expected to be in Bangladesh?

20 million due to sea level rise and increasing erosion

What is hard engineering?

The use of artifical structures that work against natural processes.

What are the types of hard engineering?

Groynes → vertical structures at 90° to the coast, which prevent longshore drift and encourage deposition

Sea walls → walls with a curved/stepped surface that absorb and reflect wave energy to reduce wave energy and erosion

Rip rap → (rock armour) resistant boulders at the base of the cliff to dissipate wave energy

Revetments → permeable sloping structures that absorb wave energy and reduce swash distance to reduce erosion

Offshore breakwaters → rock barriers in the sea to dissipate enrgy before waves hit the coast

What is soft engineering?

The use of natural materials to work with natural processes.

What are the advantages and disadvantages of hard engineering?

Advantages → obvious intervenion strategy, more long-lasting.

Disadvantages → high economic costs (sea walls cost up to £10,000), prevent natural processes (terminal groyne syndrome), money protects less area.

What are the forms of soft engineering?

Beach nourishment → adding sand/shingle to widen a beach, which dissipates wave energy and reduces erosion.

Cliff regrading + drainage → slope angles are reduced to surface erosion and water is drained to lower mass movement risk.

Dune stabilisation → fences reduce wind speed across dunes, which are replanted by with marram grass.

What are the advantages and disadvantages of soft engineering?

Advantages → works with natural processes, looks more natural, lower economic cost, can protect more area with the same monetary value, creates habitats.

Disadvantages → less longevity, beach replenishment costs up to £20 million per km

What is sustainable coastal management?

Maintaining the wider coastal zone in socioeconomic terms, whilst minimising environmental/ecological impacts

What does sustainable coastal management involve?

• Mitigation of flooding and erosion

• Adaption to erosion and flood risk

• Education of local communities

• Supporting livelihoods dependent on the coast

• Momitoring coastal changes

How can coastal management provoke conflict?

• Income may be lost from a lowered reliance on coastal resources

• Relocation might be needed when engineering is too costly

• Engineering cannot protect against all erosion/flooding

• Future trends e.g. sea level rise cannot be predicted

What is integrated coastal zone management?

Coastal management that involves stakeholders, works with natural processes and uses adaptive management.

Integrated coastal management in Indonesia

• Implemented to reduce coastal flooding, increased salinity, subsidence.

• Much of the coastal population relies on fishing, therefore are reluctant to move.

• Implemented education, mangrove conservation and drainage systems.

Who oversees UK coastal management?

DEFRA → Department for Environment, Food, and Rural Affairs

What are the four policies introduced in the 1995 Shoreline management plans?

No active intervention → no investment made regardless of pre-exsisting engineering.

Strategic realignment → allow the coastline to natural change but directing retreat to certain area.

Hold the line → build/maintain cultural defences to maintain current shoreline position.

Advance the line → build new coastal defences on the seaward side of the existing coastline.

What is cost-benefit analysis?

• Used to decide recommendations for each section of coastline

• Based on known, tangible costs of coastal defences (building and maintenance)

• Comapred with the benefit to the environment and population

Holderness Coast → cost of protecing 24 houses at Skipsea outweighs benefit

What was the cost-benefit analysis for Happisburgh?

Cost (for 600m stretch):

• Seawall £1.8 - 6 million

• Rip-rap £0.8 - 3.6 million

• Groynes £0.1 - 1.5 million

• Affected residents could receive £40,000 to 70,000 relocation expenses.

Benefit:

• 20-35 houses worth up to £7 million would be saved from erosion.

• 45 hectares of farmland worth £945,000 would be saved

What was the cost-benefit analysis for Chittagong?

Engineering:

• 2.7km retaining wall

• 69 pumps

• Improved drainage

Benefits:

• Population of 8.5 ,million saved

• Some homes and businesses would be saved from twice daily flooding from high tides.

What is an Environmental Impact Assessment?

• Identifies short-term construction impacts + long-term impacts of engineering.

• Assesses changes to: water quality, ecosystems, sediment flow, air/noise pollution.

Who are the winners and losers of coastal management?

Winners → property and businesses protected, environment conservation, protected farmland.

Losers → people relocated, lost property, lost farmland, destroyed habitats.