Coastal landscape

Coastal landscapes

Enquiry question 2: How do characteristic coastal landforms contribute to coastal landscapes?

2B.4 Marine erosion creates distinctive coastal landforms and contributes to coastal landscapes

Constructive Waves:

• Waves with low energy

• The wave height is low and flat (1m).

• Longer wavelengths (up to 100 m)

• Frequency of low wave (about 6-9 per minute)

• This implies that their swash isn't hampered by preceding backwash

• A powerful swash pushes sediment up the beach, but a weaker backwash is insufficient to convey all particles back down, thus they are deposited at the top of the beach as a ridge of sediment (berm)

• Backwash that seeps into the beach material

  • As a result of a lengthy, shallow nearshore, friction slows the wave and releases energy

  • Because of the low angle of wave contact, constructive (spilling or surging) waves have a stronger swash than backwash

Destructive Waves

• High-intensity waves

• Large wave height (more than 1 m)

• The wavelength is short (about 20 m)

• Frequency of high wave (13-15 per minute)

• They are encouraged by a short, steep nearshore zone that soon drops out into deeper water, resulting in little energy loss due to friction

• Because of the steep angle of contact, they have powerful backwash and weak swash

• Since it distributes the majority of the energy downwards and rearward, the particle orbit is more circular than constructive breakers

• Strong backwash erodes material from the beach's top, transporting it down the beach to the offshore zone

• It is frequently deposited as an offshore ridge or berm

Beach Morphology and Sediment Profiles:

Destructive Waves:

• Weak swash and vigorous backwash result in net sediment transfer along the beach, lowering the beach gradient

• Some sediment was pushed forward in a disconnected spray from a high-impact breaking wave. As a storm ridge, it accumulates above the high tide mark ​

• Backwash drove large, pebble-sized silt down the beach, forming a huge ridge of material below the low tide level at the entrance of the offshore zone

• Friction may be sufficient to induce backwash to deposit some sediment on the middle or lower beach, with the size of the deposited material decreasing towards the sea

Seasonal Variation in the UK:

• In the winter, destructive, high-energy waves dominate, reducing the angle of the beach profile and spreading shingle throughout the whole beach. Offshore ridges/bars generated by damaging wave erosion and subsequent sand and shingle deposition offshore.

• During the summer, constructive, low-energy waves dominate, steepening the beach angle and sorting particles by size, with bigger shingle particles pushed to the rear of the beach. At high tide in the summer, constructive waves form berm ridges, which are often made of gravel/shingle.

• Between berms, low channels and runnels

Daily Variation

• Storms in the summer unleash devastating waves that modify the beach profile in a matter of hours

• In the winter, calm anticyclonic conditions can create constructive waves that begin to rebuild the beach, steepening the profile for a few days before the storm

• As the wind lowers, destructive waves transform into constructive ones

• Storm beaches, which are higher in the rear of the beach, are caused by high energy deposition of extremely coarse silt during the most severe storms

2B.4B Wave Erosion Processes

Hydraulic action:

Where water's own force tears up rock

It might happen as a result of: 

• The direct impact of the water itself

• Destructive waves may produce a force of up to 50 kg/cm3

• This is enough to separate material from unconsolidated material, such as boulder clay or weak rocks like clay and shale

• The breaking wave's power squeezing air into fissures in rocks

• When the wave energy is depleted, the compressed air erupts outwards, generating micro-fractures in the rock and further widening the main break

• Small chunks of granite deteriorate and break away over time

• Alternatively, the primary fracture may expand until bigger chunks of rock collapse

The pressure drives the breach open, trapping more air and exerting additional force in the following compression cycle

It moves rock blocks from the cliff face.

Hydraulic action targeting cooling joints in hard, refractory igneous rocks may be the sole efficient wave erosion mechanism.

Corrosion

Corrosion occurs when water in the form of waves dissolves rock minerals. Minerals in solution are promptly swept away by the wave. They are also prone to erosion caused by precipitation and sea spray

Constructive waves are the most effective since the force of contact is irrelevant and the spilled wave lengthens the time it takes for the chemical reaction to occur. They are sluggish, and having a long wavelength (the longer the better) allows the rock to stay in touch with the water for a longer period of time

Carbonate rocks such as limestones (e.g., chalk, Jurassic limestone, and carboniferous limestone) and sedimentary rocks containing calcite sediment/cement disintegrate the fastest through corrosion

Attrition

• Attrition occurs when material carried by a wave is degraded by impact with other load items. It breaks down silt into tiny particles, and the repetitive contact blunts any sharp edges on the particles, making the sediment more spherical. Even harder rocks, such as quartz and granite, can be shaped into bigger rounded shingle pebbles

• It occurs in the shoreline and nearshore zones, when swash and backwash transfer sediment

• Soft rocks (e.g., loosely cemented sandstones, chalk, and clay) are readily degraded by attrition into silt and sand grains

Abrasion

• Abrasion occurs when a wave takes up silt and throws it on a rock. The constant collision wears away at the granite face, releasing minute pieces

• High-energy destructive waves with a big wave height hurl load objects with more force, resulting in quicker rates of abrasion erosion

• They require a supply of hard load objects near the foot, such as shingle from the beach

• Soft sedimentary rocks such as chalk, mudstones, and clays, as well as unconsolidated material such as boulder clay, disintegrate the fastest via abrasion

2B.4C: Coastal Landscapes Produced by Erosion

Platforms and wave cut notches (e.g. Kimmeridge Bay)

A wave cut notch is a curving depression that runs down the base of a cliff and is roughly 1-2 m high. It forms between the high and low tide lines, when damaging waves collide with the bluff.

• Hydraulic action, abrasion, and, in certain situations, corrosion degrade it

• The depth of the notch changes with the resistance of the rock at various spots

A wave-cut platform is a low-tide exposed flat rock surface that extends out to sea from the base of a cliff.

Their emergence:

• Marine erosion by abrasion and hydraulic action generates a wave-cut notch along the length of the cliff base between high and low tide

• Further erosion widens the notch until the top material falls owing to mass movement caused by gravity, producing a cliff

• The procedure is repeated, and the cliff's position shifts (coastal recession)

• The rock immediately below low tide is constantly buried; it is uneroded since it is never subjected to wave impact

• The uneroded rock at low tide level is left as a flat rock surface, the wave-cut platform, as the surrounding material is eroded

Cave-arch-stack-stump sequence:

• The geological structure of rocks includes joints, faults, and vertically sloping bedding planes

• These are eroded more quickly (e.g., by hydraulic action), and the depth and expansion of a weak spot results in the formation of a sea cave

• Caves occur on both sides of a line of weakness that runs through the headland

• The caverns are deepened by marine erosion until they meet, producing a full tunnel through the headland and forming an arch.

• Between low and high tide, hydraulic action and abrasion attack the sides of the arch, generating wave cut notch

• The undercutting of the sides causes part of the above material to fall due to mass movement, enlarging the arch

• Weathering and other sub-aerial processes are wreaking havoc on the arch roof

• The ceiling of the arch will eventually collapse due to blockfall, leaving the seaward end of the headland unattached from the land as a tall vertical column known as a stack

• Marine erosion at the tower's base will create a notch on all sides until the structure falls due to blockfall

• The stack base's remnants create a stump, a tiny rock protrusion exposed only at low tide

2B.5 Sediment transport and deposition create distinctive landforms and contribute to coastal landscapes

5A Sediment Transportation

Suspension:

When sediments stay suspended in water, this is referred to as suspension. These sediments are not so heavy that they sink to the ocean floor, nor are they so light that they float. Because these sediments are still suspended, they move with the waves, resulting in their transportation

• Where very light sediment is carried aloft within a body of water or air

• Suspended clay particles, give the sea a cloudy, muddy brown colour on soft-rock coasts, e.g. Holderness

Traction:

Traction happens when heavy materials sink to the ocean floor. Because of their weight, these sediments often just roll at the bottom of the ocean floor. However, because of the number of sediments moved, this method of coastal transportation is often sluggish

• Where large, heavy load items are rolled along the sea bed

Solution:

Minerals dissolve in seawater and are conveyed in a solution, resulting in a solution. Because the sediments get absorbed by the ocean, the load here is usually not visible. Salt, for example, is a substance that dissolves in water and contributes to the ocean's high salinity

• Where sediment is carried dissolved within the water

Current

This is the movement of water in a certain direction, and it can transport sediment in both the nearshore and offshore zones.

Winds can cause them, or changes in water density, temperature, or salinity can start them.

Sediment is transported by currents at several geographical and temporal scales:

• The global thermohaline circulation links four seas and completes one cycle in 500 years

• When the wind is blowing directly onshore and strong enough, rip currents on the beach take sediment a few metres out to sea for a few hours

Tides

• Tides are fluctuations in sea level caused by the moon's and Sun's gravitational pull

• The approaching and ebbing tides can generate tidal currents that move sediment in the nearshore and offshore zones

2B.5B Depositional Landforms

Deposition:

• Deposition happens when waves lose sufficient energy to continue transporting material

This energy loss might be caused by:

• The wind falling, reducing an energy source

• Resistance by obstacles, such as a groyne or headland

• Dissipation of energy by refraction

• Friction from lengthy transit through shallow angled nearshore and foreshore zones

Depositional landforms:

Beaches:

• ​Beaches are accumulations of sand or shingle found in the foreshore and backshore zones

• They're produced by material deposited by constructive waves

• The swash has enough strength to transport material up the beach, while the backwash only has enough energy to transport a portion of the material back down the beac h, leaving the rest deposited

Spits:

• Spits are sand or shingle beach ridges that extend into the sea beyond a curve in the shoreline (typically longer than 30') yet are attached to the land at one end

• They arise on drift-aligned beaches where the shoreline changes direction by more than 30 feet, such as at a bay or river mouth

  • Longshore drift continues in the original direction after the turn, but its energy is scattered and dissipated as the wave refracts and the current widens, resulting in deposition on the sea bottom

  • Over time, enough sediment is accumulated to break the surface, extending the beach as a spit into the sea

  • The process is repeated until equilibrium is attained at the spit's distal (seaward) end, between deposition and erosion by waves or the existing river current

• The occurrence of secondary currents generating erosion, such as the flow of a river or wave activity, determines the length of the spit

Bars and Tombolos:

A bar is a spit that connects two headlands. Bars are most visible at low tide when they become exposed. Bars make the water shallow at high tide, causing waves to break early. As a result of a bar, a lagoon may form within a bay

• Tomobolos are sand and shingle hills (or bars) that connect an offshore island to the mainland's shoreline

• Longshore drift creates a spit out from land until it meets an offshore island on drift aligned beaches

• When there is wave refraction around both sides of the island on swash aligned shores

Cuspate Forelands:

Cuspate forelands are low-lying triangular-shaped headlands produced from deposited silt that stretch out from a shoreline

Formation (there is some disagreement on this):

• When competing longshore drift currents converge at the border of two sediment cells

• Both currents dump the silt into the sea, resulting in a triangle shaped region of deposited material

They can range in length from a few metres to many kilometres

A good example is Dungeness in Kent. It stretches for 11 kilometres to the south-east, where the main west-east longshore drift meets north-south longshore drift currents caused by swell waves travelling through the North Sea into the English Channel

The Dungeness foreland is assumed to have had two spits merging at their distal ends, with a lagoon between them that was filled by salt marsh succession, wind deposition, and storm beach debris thrown up during storms

2B.5C: The Sediment Cell Model

Inputs:

Sources are locations where sediment is produced, such as cliffs or eroding sand dunes. Offshore bars and river systems, for example, are key suppliers of sediment for the coast

Some examples of sediment inputs are:

• Cliff erosion,

• Onshore currents

• River transport

• Wind blown (aeolian) sediment from land

• Subaerial processes

• Marine organisms

Transfers:

Locations where sediment moves alongshore due to longshore drift and offshore currents. This role is performed by (drift-aligned) beaches, dunes, and salt marshes

Some examples of sediment transfers are:

• Longshore drift

• Swash

• Backwash

• Tidal currents

• Sea/ocean currents

• Wind (onshore, offshore or along shore)

Feedback

• Negative feedback occurs when a change produces effects that diminish or oppose the initial change

• For example, when erosion causes blockfall mass movement. For a while, the collapsing debris functions as a barrier shielding the cliff base, delaying or halting erosion

• For example, significant erosion of sand dunes might result in excessive deposition offshore, forming an offshore bar that decreases energy and gives the dunes time to recover

Positive feedback occurs when a change has an impact that increases the original change

For example, during high-velocity storms, wind erosion of a dune area may remove stabilising vegetation

Later low velocity wind conditions cause further wind erosion, causing dune sand depletion

2B.6 Subaerial processes of mass movement and weathering influence coastal landforms and contribute to coastal landscapes

2B.6A: Weathering

Weathering is the degradation of rock in situ at or near the Earth's surface

• Subaerial processes include weathering and mass movement

• Weathering wreaks havoc on the littoral zone's backshore and foreshore

• Weathering results in the formation of rock pieces, which then combine to produce sediment

• It is particularly active in the sediment cell's source zone

Freeze-thaw weathering

• Water penetrates through rock fractures

• When water freezes, it expands by 9 percent in volume, creating a tensional force that widens the roc

• Thawing lets additional water to enter the fracture, and the procedure is repeated until big, angular pebble, cobble, or boulder-sized shards are loosened off and fissures are driven open

• Water in the pores of porous rocks may freeze, ripping off individual rock grains and forming sand-sized particle

​Biological weathering:

The breakdown of rock in situ by living or once-living creatures is referred to as biological weathering. It frequently accelerates mechanical or chemical weathering due to the operations of plants, microbes, or animals'

Weathing of tree roots:

• Rainwater and nutrients from wind-blown silt allow seeds that fall into fissures in rocks to grow

• The plant's roots extend and thicker as it develops

• The tensional stress exerted by tree roots is sufficient to enlarge the fracture

• Eventually, angular rock bits break off as cobble or boulder-sized silt

Chemical Weathering

When chemical reactions target specific minerals in a rock, they break bonds and produce new chemical compounds

Carbonation:

This assault is directed at calcium carbonate in limestones, other carbonate rocks, and sedimentary rocks containing calcite sediment

• Rainwater reacts with carbon dioxide in the atmosphere to generate mild carbonic acid (pH 5.6)

• Acidic rain reacts with calcium carbonate to produce soluble calcium bicarbonate solution

• As fresh minerals dissolve into the solution, the 'rock vanishes.'

• Only clay particles that generated imperfections in the original rock remain as sediment from limestone

• When calcite sediment weathers, previously cemented clasts are loosened, resulting in the formation of sediment

2B.6B: Mass Movement

The downslope movement of material (rock and soil) under the force of gravity is referred to as mass movement. It is a catch-all phrase describing a variety of specialised motions such as landslides, rotational slumping, and blockfall

• When the downslope gravitational force surpasses the opposing forces of friction and internal rock cohesiveness, it happens

Blockfall (or rockfall):

• Blockfall happens quickly, in a few of seconds

• They may entail the separation of single shards or the breaking up of an entire section of cliff as it descends (which occurs by the undercutting of a wave-cut notch)

• A massive blockfall occurred near St Oswald's Bay on the South Dorset Coast in April 2013, when an 80-meter piece of chalk cliff detached overnight

​Rotational Slumping:

• Rock failure and movement along a curved rock plane are involved in rotational slumping

• Slumping material normally travels as a single mass, with no internal material deformation

• It moves more slowly than blockfall, typically in 'slow-motion,' and might take minutes, hours, days, or even years (for large quantities) to occur

• Slumping is aided by the presence of water, which both increases weight (raising gravitational force) and lubricates it (reducing friction)

Landslides:

A landslide is the movement of discrete chunks of rock down a flat/linear slip plane while remaining in touch with the cliff surface

Mechanical weathering of well-joined rocks releases the individual blocks (e.g. carboniferous limestone). The loosened block is then pulled down the comparatively flat slip plane of the joint or bedding plane to the cliff foot by gravity

Landslides can also occur as a result of saltwater erosion of a cliff foot undercutting stones that have been loosened by jointing. When a support is removed, gravity is allowed to liberate the block, resulting in sliding

Rainstorms can exacerbate a landslide by lubricating the slip plane and lowering resistance

Landslides occur in consolidated rocks with slope joints or bedding planes to the sea

2B.6C: Landforms produced by Mass Movement

Blockfall:

• The angular blockfall debris forms a talus scree slope, a fan-shaped pile of material, near the cliff foot

• Undercutting cliffs with wave-cut notches can result in massive falls and talus scree slopes at their foot

• The slope angle of a talus scree slope is 34-40'. (larger fragments maintain a steeper angle of rest)

• A massive blockfall occurred near St Oswald's Bay on the South Dorset Coast in April 2013, when an 80-meter piece of chalk cliff detached overnight

• At the slope's base, a massive fan-shaped talus scree slope was formed, stretching 30 metres into the sea and protecting the cliff from further erosion for a decade or more

Rotational Slumping:

• A rotational scar is seen via rotational slumping

• A rotational scar is a new, curved, unweathered, and unvegetated cliff face rock surface

• The detached slope segment, which is frequently vegetated on top of the slump, produces a beach or terraced cliff profile

Enquiry question 3: How do coastal erosion and sea level change alter the physical characteristics of coastlines and increase risks?

2B.7 Sea level change influences coasts on different timescales

Changes in sea level in general

• The sea level is continually changing

• Because to tides, fluctuations in surface air pressure, and winds blowing on the ocean surface, temporary bulges of greater sea level are created

• Long-term sea level increases take thousands of years to occur

• Long-term sea level rise is caused by eustatic and isostatic forces, as well as tectonics

Eustatic:

• A shift in global sea level caused by a change in the amount of water in the seas is known as eustatic change

• Climate change happens cyclically, in Milankovitch Cycles, when the Earth's orbit around the Sun varies

• Glacials are 90,000 year cooler periods that result in the creation of ice sheets

• Water evaporated from the seas falls to the ground as snow and compresses to produce ice

• The distribution of water within the hydrological cycle varies throughout time, with transfers from the ocean storage to sheets on land

• A reduction in the volume of water in the seas causes a global drop in sea level.

• As a result of land-marine regression, the sea bed is revealed.

• The most recent glacial period was the Devensian, during which global sea levels were 120 metres lower than they are now. The English Channel, Irish Sea, and a large portion of the North Sea were all dry ground

Sea-level eustatic decline

During glacial eras, when ice sheets grow on land at high latitudes, water drained from the sea becomes trapped on land as ice, resulting in a worldwide drop in sea level

Sea level is rising due to eustatic forces

Melting ice sheets restore water to the sea at the conclusion of a glacial epoch, causing global sea level to increase. As the global temperature rises, the amount of ocean water expands (thermal expansion), causing sea levels to rise

Isostatic changes:

A shift in local land level is referred to as an isostatic change.

Local land level rises cause local sea level to decline. This might be because of:

• Post-glacial adaptation

• Accretion

A decrease in local land level causes an increase in local sea level. This might be because of:

• Post-glacial adaptation

• Subsidence

  • Land subsidence causes an increase in sea level

  • The weight of sediment deposition, particularly fluvial deposits in major river deltas, exceeds the threshold, resulting in extremely gradual 'crustal sag' and delta subsidence, as seen in the Nile, Mississippi, and Amazon

  • Lowering the water table (due to increased evaporation from climate change or human abstraction) can also induce settling of overlaying sediment and land subsidence when pore water pressure is eliminated.

  • Or by tall structures

Tectonics:

Eustatic

• Rising magma at constructive plate margins/hot spots elevates the underlying crust, lowering ocean capacity and causing eustatic sea level rise

• The Indian Ocean capacity was decreased due to crustal plate uplift, resulting in a 0.1 mm eustatic rise in world sea levels

Isostatic:

• Folding of sedimentary rock along a destructive plate border by compressive pressures results in an isostatic decline in sea level for anticlines and a fall for synclines. In the Bakar-Vindol region of Croatia, for example, the Alpine folding at the Eurasian-African destructive plate boundary caused an isostatic fall of 60 cm

• Isostatic fall is caused by lava or ash from volcanic activity, such as the Hawaiian hot spot island chain or the Caribbean island arc

• Spreading of the sea bottom transports volcanic islands away from the elevated crust at the mid-ocean ridge. Colder, denser crust melts, causing sea levels to increase in places like Tonga, Fiji, and Kiribati

• FAULTING may cause the HORST blocks of crust to be uplifted, resulting in an isostatic rise in land and a decrease in local sea level

• Subsidence of crust blocks caused by faulting from GRABEN, resulting in an isostatic decrease in land level and an increase in local sea level

• During the 2004 Boxing Day Tsunami in the Indian Ocean, the expansion of the crustal plate caused a 20-centimeter drop in land on the island of Sumatra in the Banda Aceh area

Emergent Coastlines

• During the Devensian Glacial, eustatic fluctuations caused a 120-meter drop in sea level.

• The beginning of the Holocene Interglacial (10,000 years ago) resulted in a fast 100 m eustatic rise in world sea levels when ice sheets and glaciers retreated after 3,000 years. This occurred over a period of around 1000 years (extremely quickly) and resulted in drowned coasts.

• The post-glacial adjustment of ice-covered land (and nearby places) was, on the other hand, significantly slower.

• Previously ice-covered territory, such as northern Britain and Scandinavia, gradually rose out of the sea.

• The Ford and Clyde valleys in Scotland's border region are now rising at a rate of 2 mm per year (though initial adjustment was faster)

Submergent coastline:

Submergent coasts are parts of the littoral zone where sea level rise has swamped formerly terrestrial territory. They may be found in southern England and throughout the east coast of the United States

• Because of the see-saw effect, areas of land next to ice-covered regions suffer isostatic uplift during the Devensian. These are currently sinking as a result of post-glacial adjustment, resulting in maritime incursion and the formation of new coasts

A ria is a drowned river valley, which is a portion of a river valley that has been inundated by the sea, making it considerably broader than would be predicted based on the river that flows into it

• The most prevalent type of coastal landform is a ria

• They are prevalent in periglacial locations near to ice-covered land during the Devensian period, such as Southern England

• When rivers overflowed, they cut steep-sided V-shaped valleys into the frozen terrain, giving the ria a V-shaped cross section

• The undulating plan profile of rias reflects the meandering river channel. As tributaries are swamped by the increasing sea, the plan view becomes dendritic

• A ria is a type of estuarine shoreline

• The Kingsbury Estuary on the south Devon coast, for example, is a 6 m long ria. Near its mouth in Salcombe, the main canal is 1 m wide. Frogmore Creek, a 2 km long and 500 m broad drowned tributary, extends from the east side of the ria

2B.7C Contemporary Sea Level Change

Climate change causes eustatic sea level rise

• Warming causes mountain glaciers (Alps, Himalaya) and polar ice sheets to melt, increasing the amount of water stored in the ocean.

• Because the ice was already displacing the comparable water volume as that generated by melting, melting had no effect on sea level.

• The IPCC blames 50% of sea-level increase between 1990 and 2010 to melting ice sheets (Greenland ice sheet 15 percent , Antarctic ice sheet 10 percent )

The remaining 10% of sea level increase was caused by tectonic activity:

• Underwater volcanic activity can promote thermal expansion of ocean water by emitting geothermal heat into the oceans

• Rising magma near constructive plate borders causes a doming upwards of crust along mid-ocean ridges, which reduces the volume of the ocean basin

At destructive margins:

• Plate tectonics expands ocean basin volume, decreasing sea levels

• Earthquakes at the border can allow the non-subducting margin to recover. - Seafloor uplift lowers ocean volume, rising sea levels

• The 2004 Boxing Day tsunami, with a magnitude of 9.3, elevated parts of the Indian Ocean floor, elevating sea levels by 0.1 mm

It can also cause isostatic change:

• Faulting can raise portions of the crust, reducing sea levels (or vice versa), by up to 2 metres

• Turakirae Head on New Zealand's North Island was raised 6 metres by the 1855 earthquake

• Sea floor spreading takes volcanic islands away from the raised crustal zone along constructive boundaries or hotspots - to locations where the ocean bottom is colder, denser, and lower lying - islands sink

Which coastlines are in danger?

• Low-lying areas - coastal flooding caused by marine transgression

• Low-lying volcanic islands or coral atolls perched on top of submerged volcanic guyots

• Maldives in the Indian Ocean, Kiribati Islands in the Pacific Ocean, for example, are on the verge of extinction

• Volcanic islands are being threatened by both global warming and tectonic action

2B.9 Coastal flooding is a significant and increasing risk for some coastlines

2B.9A - Local Factors that Increase Coastal Flood Risk

Because of the following reasons, sea level rise impacts a disproportionate number of people:

• Because beaches and the water attract a huge number of tourists, many low-lying coasts are heavily inhabited

• Low-lying deltas are exceptionally productive and suitable for agriculture. Estuaries and deltas are useful for trade because they provide good navigable access interior up rivers

• Many river deltas are home to megacities

  • Shanghai, Yangtze Delta China - 24 million people

  • Dhaka, Bangladesh, Ganges-Brahmaputra delta - 14 million people

  • Karachi, Pakistan Indus delta - 23.5 million people

Local factors:

Height:

• Low-lying coasts are just 1-2 m above (high tide) sea level, putting them at risk of floods

• Storm surges pose a temporary flood danger, whereas global sea level rise poses a persistent flood risk

• The Maldives archipelago in the Indian Ocean is home to 340,000 people scattered across 1,200 islands

  • The Maldives' highest point is merely 2.3 metres above sea level

  • Malé, the major island and capital, is surrounded by a three-meter-high sea wall

• Bangladesh is located in the Ganges-Brahmaputra delta, and 60% of the nation is less than 3 metres above sea level

• Kiribati is a Pacific Ocean archipelago made up of 33 coral atolls

Subsidence:

• Natural subsidence occurs along low-lying coasts in estuaries, deltas, and outbuilding zones due to the settling and compaction of previously deposited silt

• However, subsidence is frequently exceeded by new deposits and organic matter bioaccretion

• Deltas endure periodic isostatic subsidence when the weight of the delta sediment reaches a critical level that causes the crust to sink, resulting in marine transgression and flooding

Local subsidence can also be caused by human activity:

• Drainage of saturated sediment/soil for agriculture, such as in the Fens of East Anglia, or ground water abstraction for city supply, such as in Venice, lowers sediment volume and promotes subsidence

• Subsidence can occur as a result of the weight of cities and the built environment compressing sediment (also happening in Venice)

• Land reclaimed from the sea, such as the Ijsselmeer polders in the Netherlands, is prone to subsidence owing to water abstraction by agricultural crops via evapo-transpiration

Vegetation Removal:

• Flood danger is reduced by vegetation such as salt marshes and mangrove forests

• Vegetation both stabilises existing sediment and traps additional material, elevating the land's elevation above sea level

• Vegetation absorbs wave energy, minimising wave impact and erosion, as well as shortening the distance waves travel ashore before their energy is depleted

• A 100 m mangrove forest belt is expected to lower wave height by 40%

• A 1 km mangrove forest belt minimises storm surge height by 0.5 m

• Since 1950, an estimated 50% of the world's mangrove forest has been eliminated - 1/4 of the loss for the development of shrimp farms, and plenty gone for tourist beaches

• The Sundarbans, a 180-kilometer-long mangrove forest in Bangladesh, is the world's biggest. However, 71% of the land is being cleared of vegetation. Some parts are deteriorating at a rate of 200 m p.a

2B.9B - Storm Surges

On low-lying beaches, storm surges can cause significant coastal flooding

Storm surge water's onshore current can cause fast coastal erosion

Storm surge's impact is exacerbated by enormous damaging waves whipped up by powerful storm winds on top of already rising sea levels And fast coastal erosion

Short term inpacts:

• People are killed or injured as a result of drowning or falling structures

• Deaths as a result of hypothermia (homes destroyed), water-borne infections (sewer systems and freshwater pipes destroyed), and natural causes (transport routes to medical care cut)

• Infrastructure destruction - roads, trains, ports, and airports flooded or destroyed

• Water pipelines, transmission lines, and sewage systems have all been damaged, resulting in a lack of power and water

• Homes destroyed - older houses have lower standards and are less expensive in impoverished places - homes on marginal low lying ground (slums and shanty towns) are the most vulnerable - rebuilding may take many years, with the wealthy (who have insurance) likely to be rehoused first.

• Businesses destroyed - factories, offices - power outages, disruptions in raw material delivery, workers killed/injured/unable to arrive - agricultural land contaminated - crop harvest lost

2B.9C - Climate Change and Coastal Flood Risk

The future (High confidence):

• By 2100, the sea level will have risen by 18-59 cm

• However, due to population expansion, economic development, natural positive and negative feedback, and political resolve to limit GHG emissions, the rate and amount of sea level rise within the expected range are unpredictable

It can also be affected by adaptation:

• Constructing sea walls, for example, on the North Norfolk coast, 3 m sea wall on Malé

• Hulhamalé, a new artificial island constructed by the reclamation of sand from the sea bottom between 1997 and 2002, is 4 metres above sea level and cost $32 million to build.

• Constructing earthen embankments, such as the bunds in Bangladesh

• Storm surge barriers over river mouths - in the Netherlands, the Thames Barrier and the Eastern Scheldt Barrier (part of the 2.5 billion euro project begun after the 1953 storm surge)

• Mangrove forest restoration - protective belts, for example, in Sri Lanka, replanting after the 2004 Indian Ocean tsunami killed 6,000 people in one coastal hamlet where mangroves were removed, but just 2 died in a neighbouring community protected by a mangrove forest

• Mitigation - measures to lessen the size of an incident. Reducing greenhouse gas emissions to minimise global warming would reduce sea level rise and storm severity

The future (Medium confidence):

Wind and waves

• There has been some indication of increased wind speeds and high waves

Coastal erosion

• Erosion will typically rise as a result of the combined effects of weather system and sea level changes

The future (Low confidence):

Tropical cyclones:

• The frequency is expected to stay constant, although there may be more big storms

• Strength is expected to improve by 2-11 percent by 2100. Rainfall will rise by 20% as a result

• The strength of cyclones would rise owing to increased ocean surface temperatures and a warming atmosphere that held more moisture

• The number of tropical cyclones is not expected to rise since they are formed by a combination of causes, one of which is warm water temperatures

• The number of tropical storms that become hurricanes in the North Atlantic increased from six in the 1900s to eight each year from 2000 to 2016

• However, this is simply a low-confidence estimate because no rise in maximum intensity has been detected in the Pacific and Indian Oceans over the previous 20 years of observation

• The frequency and severity of tropical cyclones vary greatly from year to year and decade to decade; there is no statistically significant long-term trend

Storm surges:

• These are connected to depressions, which are expected to grow more widespread in the future

• More powerful tropical cyclones will have even lower surface air pressure, resulting in bigger temporary sea level rises as storm surges and an increased danger of coastal flooding

Enquiry question 4: How can coastlines be managed to meet the needs of all players?

2B.10 Increasing risks of coastal recession and coastal flooding have serious consequences for affected communities

2B.10A - Economic and Social Losses from Recession

Economic:

• Property loss (or damage) in the form of houses, companies, and farmland is very straightforward to calculate. The losses are often localised, and the expenses are determined by the land's usage and location

• The EA valued English agricultural land at £21,000 per hectare in 2015, and industrial/business land at £500,000 per hectare

• The cost of residential land can range from £500,000 (North Yorkshire, cold climate, boulder clay) to £2.1 million per hectare (Dorset, warm climate, Jurassic coast)

• A two-lane road re-routing can cost between £150,000 and £250,000 every 100 m. The restoration of a stretch of shoreline supporting the South Devon Main Line Railway that collapsed in February 2014 cost £35 million, and firms in the South West lost £60 million

Social:

Relocation

• The price (can be quantified)

• Community disintegration, loss of friends and interests such as a football team or classes

• It's also stressful

Loss of livelihoods:

• Income source (can be quantified)

• Stress is caused by financial difficulties and the quest for a new career

Other consequences:

• Businesses may suffer financial losses if locations become unappealing and depopulate

• A whole town might be jeopardised 

• Property values are falling, and it is becoming increasingly difficult to sell property

• The loss of a big asset, as well as the price of purchasing a replacement house

• Incapability to insure against loss

2B.10B - Consequences of Coastal Flooding and Storm Surges

Flooding and storm surges are both one-time occurrences that might happen decades apart. Flooding has a bigger area of effect and causes more damage; in some situations, it might be considered as a natural catastrophe. A storm surge is a transient rise in sea level caused by very low surface air pressure, which causes short-term coastal flooding, which is particularly severe in tropical latitudes

They endanger much more people than coastal erosion (which only affects a few individuals directly), and they have far-reaching economic and social implications

Consequences in a HIC (Australia):

The IPCC predicts a sea level increase of 28-98 cm by 2100, with a 55 cm rise being the most likely

A 1M rise would flood:

• 116,000 homes causing property damage of US $72 billion;

• $87 billion worth of commercial property threatened

• $67 billion road and rail infrastructure.

• 5 power stations,

• 258 emergency service stations,

• 75 hospitals and

• 44 water and sewage plants

The social costs would include community disintegration, loss of livelihood (e.g., fishing, tourism), and amenity loss 

The Great Barrier Reef's coral reefs will die if they are unable to develop quickly enough to keep up with sea level rise, resulting in a loss of tourism revenue

Consequences in a LIC (Philippines):

The IPCC predicts a rise of 60 cm - 1 m in the Philippines by 2100

Economic:

• A one-meter increase would result in $6.5 billion in property damage

• San Fernando in northern Luzon is expected to lose 123,000 m2 of beach with $95,000 p.a. in tourism earnings. Losses in the fishing business are anticipated to reach $168,000 p.a

• Much of the affected region consists of impoverished shanty settlements, such as Cavite City and Las Pias near Manila, with low property values

Social:

• A one-meter increase will harm 2.3 million people and 62 percent of Manila on Luzon Island's southern coast

• Loss of a source of income - fishing, tourism

• San Fernando Beach's amenity value has declined

• The social cost is substantial since alternative work in the formal sector is scarce

Typhoon Haiyan

With a 4-5 m surge, it was one of the most violent tropical storms ever recorded

Economic:

• Damages totaling over $2 billion USD, with the city of Tacloban

• In Tacloban, 90% of structures have been destroyed or damaged

Social:

• At least 6,300 people have died

• 30,000 people were injured, and 1.9 million people were made homeless

• 6 million people have been affected, with 20,000 fleeing to Manila

2B.10C - Environmental Refugees

Environmental refugees are persons who have been forced to flee their homes due to natural processes, which might be rapid, such as landslides, or gradual, such as erosion or increasing sea levels. The United Nations High Commission for Refugees does not use the word. It comprises refugees as well as internally displaced persons

According to the IPCC, climate change would cause a 26-82 cm rise in sea level by 2100, resulting in environmental refugees by:

• Flooding

• Encroachment of salt water (into groundwater, for drinking, irrigation and industry)

• Bleaching of coral reefs (which acts as a sea defence)

The Maldives, Tuvalu, the Seychelles, and Barbados are the places most vulnerable to the expected sea level increase by 2100

Tuvalu's highest point is 4.5 metres above sea level, while most of the land is barely 1-2 metres above sea level.

As its land area shrinks due to rising sea levels, New Zealand grants residence to 75 Tuvalu people each year through the Pacific Access Category Ballot.

In 2014, the Alesana family was awarded permanent residency in New Zealand by the courts on the grounds that they were climate change refugees

• The shoreline is home to 80 percent of the inhabitants in the Seychelles

• Coral reefs, which serve as a natural coastal defence against erosion, are being decimated by coral bleaching caused by global warming

• Water supply is limited and vulnerable to salt-water intrusion as sea levels rise, and groundwater is overutilised

• Their economies are tiny and restricted, dependent on tourism and fishing, and are quickly disturbed

• They have enormous population densities and relatively little space, thus there is no way to relocate

• Developing or rising countries lack the resources to fund coastal defences that would safeguard vast stretches of coastline

• The Maldives have an average elevation of 1.5 metres above sea level, yet the 400,000-person population is too enormous to be readily accommodated elsewhere. Its government is considering land purchases with India, Sri Lanka, and Australia