COASTS CONTENT

The coastal system

• open system as it receives inputs from outside the system and transfers outputs away from the coast and into other systems

• May be terrestrial, atmospheric, or oceanic and can include the rock water and carbon cycles

Sediment cells

• often bordered by prominent headlands

• Movement of sediment is contained within sediment cells and the flows act in dynamic equilibrium

Inputs to the coastal system

• material/energy inputs

• Three main areas:

• Marine: waves, tides, salt spray

• Atmosphere: sun, air pressure, wind speed/direction

• Humans: pollution, recreation, settlement, defences

Outputs to the coastal system

• material/energy outputs

• Ocean currents

• Rip tides

• Sediment transfer

• Evaporation

Stores/sinks in the costal system

• stores/sinks of sediment/material

• Beaches

• Sand dunes

• Spits/bars/tombolos

• Headlands/bays

• Nearshore sediment

• Cliffs

• Wave cut notches/platforms

• Caves/arches/stacks/stumps

• Salt marshes

Transfers/flows in the coastal system

• processes that link the inputs, outputs and stores

• Wind blown sand

• Mass movement

• LSD

• Weathering

• Erosion

• Transportation

• Deposition

Sediment sources

• rivers: account for majority of sediment in the coastal zone

• Cliff erosion: mostly occurs in inter due to more frequent storms

• Wind: can cause sand to be blown along or up a beach

• Glaciers: can flow directly into the ocean depositing sediment that was stored in the ice

• Offshore

• LSD: sediment moved along the beach due to prevailing wind which alter the direction of waves

Sediment budget

• assess the gains and losses of sediment within a sediment cells

• In principle, a system operates in a state of dynamic equilibrium where inputs=outputs

• However human action and natural variation an disrupt the state of equilibrium

The littoral zone

Area of land between the cliffs or dunes on the coast and the offshore area that is beyond the influence of the waves

What impacts the littoral zone?

• short term factors: tides, storm surges

• Long term factors: changes in sea level and human intervention

Wave formation

• occur when wind moves across the surface of the water, causing frictional drag, making small ripples and waves

• This leads to a circular orbital motion of water particles in the ocean

• As the seabed becomes shallower, the orbit of the water particles becomes more elliptical, leading to horizontal movement of the waves

• The wave height increases, but the wavelength and wave velocity decrease

• This causes water to back up from behind the wave until it breaks and surges up the beach

Factors affecting wave energy

• wind strength: the larger the pressure gradient between two areas, the stronger the wind.

• Duration of wind: if he wind is active for longer periods of time, the enegry of waves will build up and increase

• Fetch; distance over which the wind blows. Larger fetch=stronger waves

Constructive waves

• build up a beach and increase its size

• Long wavelength

• 6-9 per minute frequency

• Low waves which surge up the beach

• Strong swash, weak backwash

• Occurs on gently sloped beaches

Destructive waves

• remove the beach and decrease its size

• Short wavelength

• Formed in localised storm events with stronger winds operating closer to the coast

• 11-16 per minute frequency

• High waves which plunge onto the beach

• Weak swash, strong backwash

• Occurs on steeply sloped beaches

Negative feedback loop: beaches and waves

• presence of constructive waves causes deposition on the beach which leads to the beach profile becoming steeper

• Steeper beaches favour the formation of destructive waves making them more likely to occur

• The destructive waves erode the beach reducing the beach profile and leading to the formation of constructive waves

Tides

• gravity is a key source of energy in coastal environments

• SPRING TIDE: The highest high tide and lowest low tide occur when the sun and moon are in alignment to each other so their gravitational forces work with each other. Creates the largest possible tidal range

• NEAP TIDE: lowest high tide and highest low tide occur when the sun and moon are perpendicular to each other so their gravitational forces work against each other. Creates the smallest possible tidal range

High energy coastlines

• associated with more powerful waves so occur when there is a large fetch

• Typically have rocky headlands and landforms

• Fairly frequent destructive waves

• Often the rate of erosion exceeds the rate of deposition

Low energy coastlines

• less powerful waves and occur in sheltered areas where constructive waves prevail

• Fairly sandy areas

• Landforms of deposition as deposition exceeds erosion

Wave refraction

• waves turn and lose energy around a headland on uneven coastlines

• Wave energy focused on headlands, creating erosive features in these areas

• Energy dissipated in bays leading to formation of features such as beaches

Corrosion

Sand and pebbles picked up by the sea from an offshore sediment sin or temporal store and hurled against the cliffs at high tide

Abrasion

Sediment moved along the shoreline, causing it to b worn down over time

Hydraulic action

As a wave rashes onto a rock or cliff face, air is forced into cracks, and the high pressure causes the cracks to force apart.

Solution

Mildly acidic seawater can waist alkaline rock such as limestone to be eroded

Wavequarrying

When breaking waves hit the cliff face to directly pull away rock from a cliff face or remove smaller weathered fragments

Factors affecting erosion

• waves

• Beach size and presence

• Activity of subaerial processes

• Rock faults

• Rock lithology

Traction

Large heavy sediment rolls along the sea bed pushed by currents

Saltation

Smaller sediment bounces along the sea bed

Suspension

Small sediment carried within the flow of the water

Solution

Dissolved material is carried within the water

LSD

• waves hit the beach at an angle determined by the direction of the prevailing wind

• The waves push sediment in this direction and up the beach in the swash

• Wave carries sediment back down the beach in backwash

• Moves sediment along the beach over time

Deposition

• occurs when sediment becomes too heavy for water to carry or if the wave loses energy

• Is a gradual and continuous process

• High energy coastlines deposit larger rocks and shingle ad continue to carry smaller sediment

• Low energy coastlines deposit much smaller sediment

Weathering

• breakdown of rocks over time leading to the transfer of material in the littoral zone, where it becomes an input to sediment cells

Mechanical weathering

• breakdown of rocks use to exertion of physical forces

• Freeze-thaw: water enters cracks in rocks then the freezes overnight during winter. Water expands by 10% in volume when freezing whcih increases pressure on the rock, causing cracks to develop. Over time the cracks grow and makes the cliff more vulnerable to other processes of erosion

• Salt crystallisation: as seawater evaporates, salt is left behind. Salt crystals grow over time, exerting pressure on the rock, forcing cracks to widen.

• Wetting and drying: rocks such as clay expand when wet and contract again when they ar drying. Frequent cycles of wetting and drying can cause cliffs and rocks to break

Chemical weathering

• carbonation: rainwater absorbs CO2 from the air creating carbonic acid, which reacts with calcium carbonate in rocks to form calcium bicarbonate which can be easily dissolved. Acid rain reacts with limestone forming calcium bicarbonate, which is easily dissolved allowing erosion

Biological weathering

• plant roots: roots of plants growing into cracks of rock exert pressure and eventually split rock

Mass movement

• movement of material down a slope under the influence of gravity

• Acts as an input into the littoral zone from the store of the land

• Dependent on:

  • Cliff/slope angle

  • Rock type and structure

  • Vegetation

  • Saturation of ground

  • Prescience of weathering

Soil creep

• slowest but most continuous form of mass movement

• Particles of soil fall due to wetting and freezing, causing the soil to move down the slope

Mudflows

• increase in water content of soil reduces friction, leading to mud flowing over underlying bedrock

• Represent a serious threat to life as they can be fast flowing

Rockfall

• occurs on sloped cliffs over 40 degrees when exposed to mechanical weathering and can be triggered by earthquakes

• Leads to scree (rock fragments) building up at the base of the slope

Landslide

• heavy rainfall leads to water between joints and bedding planes in cliffs which can reduce friction and lead to landslide

• Block on intact rock moves down the cliff face very quickly

• Can be very dangerous

Slump

• occurs on a curved slope (often in weak and unconsolidated clay and sand areas)

• Build up in pore water leads to the land collapsing under its own weight

• Creates a terraced appearance on the cliff face

Cave, arch, stack, stump

• Occurs on pinnacle headlands

• Faults in headland eroded by hydraulic action and abrasion, forming small caves

• Overlying oak in teh cave may collapse forming a blowhole which spurts out water when a wave enters the base, forcing sea spray and air out of the top

• Marine erosion widens faults in the base of the headland forming the cave

• Eventually the cave will be eroded through to the other side of the headland, creating an arch

• Arch continues to widen until it cannot support its weight, falling by mass movement leaving a stack which is detached from the mainland

• Marine erosion attacks the base of the stack, eventually collapsing into a stump

Rate of retreat

• dependent of relative importance of marine factors (fetch, beach, wave and energy) and terrestrial factors (subaerial processes, geology, rock strength)

• Cliffs made of unconsolidated rock and sand are more likely to retreat

Wave-cut notch and platform

• wave erosion concentrated around the high tide line

• Processes of hydraulic action and corrosion create a wave cut notch

• AS the notch becomes deeper and subaerial weathering weakens the cliff from the top, the cliff face becomes unstable and falls under its own weight through mass movement

• This leaves behind a platform whcih is normally exposed at high tide

Beaches as accretion/excavation

• beaches are depositional landforms that stretch from the low tide to high tide line

• Most important store in te coastal system

• Beach accretion occurs when the beach is built up by constructive waves (normally during summer months)

• Excavation occurs in winter when destructive waves remove sediment

Swash aligned beaches

• wave crests approach perpendicular to the coast so there is limited LSD

• Sediment does not travel fa along the beach

• Wave refraction may reduce the speed of high energy waves, leading to the formation of a shingle beach wit larger sediment

Drift aligned beach

• waves approach at an angle so LSD causes sediment to travel far along the beach which may lead to formation of a spit

• Larger sediment found at the start of the beach and weathered sediment moves along it, becoming smaller, so the end of the beach will have smaller sediment

Spits

• long narrow strip of land whcih is formed when LSD causes beach sediment to extend out to sea usually due to change in direction of coastline

• May create a salt marsh due to the sheltered saline environment where water slow sped is lower, allowing deposition of finer sediments to occur

• Change in wind direction can cause a recurved end on the spit

Barrier beach/bar

• occurs when a beach or spit extends across a bay to join two headlands

• Traps water behind it leading to formation of a lagoon

• If it becomes separated from the mainland, it becomes a barrier island

• Common in areas with low tidal ranges eg the Netherlands

Tombolo

• bar or beach that connects the mainland to an offshore island

• Formed due to wave refraction off the coastal island reducing wave velocity,leading to deposition of sediments

• May be covered at high tide if they are low lying

Offshore bars

• offshore region where sand is deposited as the waves dont have enough energy to carry sediment to shore

• Can be formed when the wave breaks early, instantly depositing its sediment as an offshore bar

• Waves may pick up sediment from an offshore bar, providing an important sediment input into the coastal zone

• May absorb wave energy, reducing erosion in some areas

Plant succession

• plant community that changes over time

• Pioneer plants grow in bare mud and sand on coasts where there is a supply of sediment and deposition occurs

Plant succession in sand dunes

• embryo dunes colonised by pioneer plants (salty, nutrient poor sand and harsh conditions)

• Pioneer plants die and release nutrients into the sand, increasing amount of vegetation able to grow within the dune

• New species pf plants now colonise the area, changing the environment progressively

• Eg marram grass is a pioneer plant, as it is tough and flexible, adapted to water loss through transpiration, and roots grow up to 3m deep

Salt marsh succession

1. Algal stage: blue green algae establish as they can grow on bare mud which helps their roots bind

2. Pioneer stage: cord grass roots begin to stabilise the mud allowing the estuarine to grow

3. Establishment stage:salts marsh grass grows creating a carpet of vegetation so height of the salts marsh increases

4. Stabilisation: sea thrift grows and rarely gets submerged beneath the marsh

5. Climax vegetation: rush grows since the salts marsh is only submerged ½ times a year

How does vegetation help stabilise coastal sediment?

• roots of plants bind soil together, reducing erosion

• provide a protective layer for the ground so it is less easily eroded

• Reduce wind speed at surface so less wind erosion occurs o

Sand dunes

• occur when prevailing winds blow sediment to the back of the beach

• Require large quantities of sand and a large tidal range

• Allows the sand to dry so that it is light enough to be picked up and carried by wind to the back of the beach

• Frequent and strong onshore winds necessary

Dune structure

1. Embryo dunes: upper beach area where sand starts to accumulate around a small obstacle eg driftwood

2. Yellow dunes: more sand accumulates causing the dune to grow. Vegetation may develop which stabilises the dune

3. Grey dunes: sand develops into soil with lots of moisture and nutrients as vegetation dies, enabling more varied plant growth

4. Dune slack: water table rises closer to the surface, or water is trapped between hollows between dunes during storms, allowing development of plants such as willow grass

Isostatic change

• occurs when land rises/falls relative to the sea and is localised change

• Often a result of Isostatic subsidence (glaciers weighing down land beneath so the land subsides)

• When glaciers melted, it caused Isostatic recovery and the coastline to rebound and rise again in areas that were covered by ice

Isostatic change in the UK

• Scotland and the north west of England are rising at around 1.5mm per year as they were previously covered by glaciers

• This has caused the south east to subside by around 1mm per year

Tectonic activity and Isostatic change

• tectonic activity such as earthquakes and volcanic eruptions may cause land subsidence, therefore causing Isostatic sea level change.

• Eg 2004 Indian Ocean earthquake caused the city of Bandeh Aceh to sink permanently by 0.5m

Eustatic change

• affects sea level across the planet

• May be due to thermal expansion/contraction or changes in glacial processes

• Thermal expansion = water expanding when it warms, so the volume of water increases leading to rising sea levels

• Sea levels in the last ice age were 100m lower than now due to water being stored in ice caps and majority of precipitation being snow

• Due to global warming, IPCC predicts sea levels rise from 0.3-1m by 2100

• Eg Miami are facing significant problems of the coastal strip flooding during high tides as a result of rising sea levels

Emergent coastal landforms

• where land has been raised in relation to the coastline, landforms such as arches, stacks, and stumps may be preserved

• Raised beaches are common before cliffs which are also raised (relic cliffs), with wave-cut notches and similar features proof of historical marine erosion

Submerge my coastal landforms

• occur when the sea level rises or the coastline sinks in relation to the sea

Rias

• formed when rising sea levels flood narrow winding inlets and river valleys

• Deeper at the moth of the inlet

• water depth decreases further inland

Fjords

• formed when rising sea levels flood deep glacial valleys to create natural inlets and harbours

• Found in New Zealand

• Deeper in the middle section than the mouth

Dalmatian coasts

• occurs when valleys running parallel to the coast become flooded as a result of sea level change

• Leaves a series of narrow, long islands

• Seen in Croatia

Coastalisation

• process n which th coast is being developed and people are moving to the coast, increasing the number of people at risk from marine related environmental activity

• May be a byproduct of urbanisation as majority of large cities are coastal

Storm surges

• potential to inundate flood defences

• Risk from storm surge may be exacerbated by:

  • Removing natural vegetation: eg mangroves whcih provide protection to coastlines like the Bay of Bengal. Many mangrove forests being destroyed for tourism or housing

  • Global warming: severity of storm surges likely to increase

Consequence of risk for communities

• some areas of coast significantly reduced house and land prices due to associated risks leading to economic loss for homeowners and local coastal economies

• Many insurers dont provide home insurance to people living in high risk coastal areas

Impact of storm surges environmentally

• destroy plant succession and damage coastal landforms

• Depositional landforms likely to be destroyed

• Eg in 2013 when Spurn Point (spit) was partially destroyed by a large storm surge

• Destruction of depositional landforms may cause erosion rates to increase and closer to the cliff face, increasing risk of cliff collapse and threats to land owners

Coastal environmental refugees

• more than 1 billion live on coasts at risk of coastal flooding

• 50% f the worlds population live within 60km of coast

• Around 75% of worlds large cities are coastal

• Increase in storm surges and erosion on coasts will increase environmental refugees displaced internally/internationally

Hard engineering

• man made structures that aim to prevent erosion

• Often effective however are high cost and have significant environmental impact due to use of materials such as concrete

• Only prevent erosion in one area and may exacerbate erosion elsewhere

Offshore breakwater

• rock barrier which fires waves to break before reaching the shore

• Effective at reducing wave energy

• Visually unappealing

• Navigation hazard for boats

• Can interfere with LSD

Groynes

• timber or rock protrusions that trap sediment from LSD

• Builds up beach

• Protects cliff and increases tourism potential

• Cost effective

• Visually unappealing

• Deprives areas downwind of sediment, increasing erosion elsewhere

Sea walls

• concrete structures that absorb and reflect wave energy

• May b curved

• Effective erosion prevention

• Promenade has tourism benefits

• Visually unappealing

• Expensive to construct and maintain

• Wave energy reflected elsewhere

RIP rap/rock armour

• large rocks that reduce wave energy but allow water to flow through

• Cost effective

• Rocks are sourced elsewhere so do not fit with local geology

• Pose hazards to humans if climbed on

Revetments

• wooden or concrete ramps that help absorb wave enegry

• Cost effective

• Visually unappealing

• Can need constant maintenance requiring additional costs

Soft engineering

• aims to work with and complement the physical environment by using natural methods of coastal defence

• Useful for protecting against sea level change as well as coastal erosion

Beach nourishment

• sediment taken from offshore sources to build up existing beach

• Protects cliff nd increases tourist potential

• Cost effective and looks natural

• Need constant maintenance

• Dredging may have consequences on local coastal habitats

Cliff regrading and drainage

• reduces angle of the cliff to help stabilise it (Steeper cliff more likely to collapse)

• Cost effective

• Cliff may collapse suddenly due to being drier

• May look unnatural

Dune stabilisation

• Marram grass planted

• Roots help bind the dunes, protecting land behind

• Cost effective and creates important wildlife habitats

• Planting is time consuming

Marsh creation

• type of managed retreat allowing low lying areas to flood

• Creates important wildlife habitat

• Farmers lose land and may need compensation as a result

Cost benefit analysis (CBA)

• carried out before any management takes place

• Expected cost of construction/demolition/maintenance

• May be tangible or intangible

• According to DEFRA’s 1:1 analysis, expected benefits must out way the costs for a project to go ahead

Sustainable coastal management

• holistic strategies that recognise all sections of coast are interlinked and function as a whole

• Includes:

  • Managing natural resources like water and farmland to ensure long term productivity

  • Ensuring there are new jobs for people who may face unemployment as a result of protection methods

  • Monitoring coastal changes and using adaptation or mitigation as a response to observed change

  • Educating communities about how to adapt and protect coastal for future generations

  • Ensuring everyone is considered when changed are proposed

Integrated coastal zone management (ICZM)

• method of sustainable coastline management

• Large sections of coastline (often sediment cells) are managed with one integrated strategy

• Occurs between different political boundaries eg in the UK different councils will have to work and manage coasts together

Features of ICZM

• recognises the importance of the cost for peoples livelihoods

• Recognises management must be sustainable where economic development is important but must not be prioritised over protection of the coastal environment

• Must involve all stakeholders, plan for the long term and try to work with natural processes, not against them

• Recognise decision to protect one coastal community may not outweigh the disadvantages of exposing another community to increased erosion

• Eg in 2013 the EU adopted a new initiative which promotes the use of ICZMs across all of europe’s coastlines, which recognised the benefits of the ICZM strategy

Shoreline Management Plans (SMPs)

• created for each sediment cells in the UK

• Each SMP identifies all of the activities, both natural and human which occur within the coastline of the sediment cells

• Sediment cells considered closed systems for the purpose of management

• Recommended for all sections of English ad Welsh coastlines by DEFRA

SMP management options

• hold the line: defences used to maintain current position of shoreline

• Managed retreat: defences used o allow coastline to advance inland and create its own natural defences eg salt marshes

• Advance the line: defences built to try move the shoreline seawards

• No active intervention; coastline left exposed to natural processes

Factors considered when choosing an SMP management method

• economic value of assets that could be protected. Eg a know area of gas reserves more likely to be protected than a caravan park

• Technical feasibility of engineering solutions (sea wall may not be suitable for some locations)

• Ecological and cultural value of land (may be desirable to protect historic areas and Sites of Special Scientific Interest (SSSI))

Conflict over policy decisions

• may be winners and losers

• Winners benefit economically, environmentally, and socially

• Losers may lose property, employment, and may have to relocate

• DEFRA funding has been reduced by central government since 2010 so now have to prioritise funding in most important locations

Impact of sea walls on sediment cells example

• installing a sea wall would reflect wave energy downdrift increasing wav energy and erosion elsewhere on the coastline

• Less erosion occurs in area with the sea wall, so there is less sediment in areas with increased wave energy

• Less sediment reduces beach size so cliff is more exposed to erosion