Coasts

Closed system - an input and output of energy but not matter e.g. earth

Open system - inputs and outputs of both energy and matter e.g. coasts

Dynamic equilibrium - when system has balance of inputs and outputs

Feedback - a change in the impact or output that upsets the dynamic equilibrium

Positive feedback - a sequence of events that increases change and instability

Negative feedback - a sequence of events that damp down the effects of change + promotes stability and a dynamic equilibrium

Inputs:

• sediment - brought in through rivers, sea level rise, erosion + offshore deposits
• energy - wind, waves, tides, currents

Outputs - sediment washed out to sea or deposited further along coast

Flows/transfers - sediment moved within system e.g. erosion, weathering, transportation + deposition

Stores/components - sediment stored in landforms such as beaches, dunes + spits

Fetch - distance of open water which wind blows uninterupted

Prevailing wind - controls direction waves approach coast

Wave charactersitics from - fetch, wind duration + wind strength

Wave formation:

• wind creates friction when air mass hits water, causing ripples that increase in size and move in circular motion
• as waves grow more surface area to blow on and therefore grow with positive feedback
• when waves start to feel bottom the circular motion below waves start to compress, friction slowed down so bunch up (wavelength decreases)
• height increases as energy forced upwards (wave height increases)
• energy released when waves break

Wavelength - from one crest to another

Wave height - from trough to crest

Wave refraction - as waves approach a coast they're refracted so energy concentrated around headlands but reduced around bays as their energy decreases as water depth decreases

Destructive waves:

• created in storm conditions when wind powerful and blowing for long time
• occur when wave energy high with long fetch
• erode coast
• stronger backwash than swash
• short wavelength, high + steep

Constructive waves:

• created in calm weather + less powerful
• break on shore + deposit more than erode, building up beaches
• swash stonger than backwash
• long wavelength and low in height

The physical properties of a rock e.g. its resitance to erosion

Hard rocks e.g. Gabbro are resistant to weathering so change will be slower e.g. Land's End

Soft rocks e.g. Limestone will weather and change more quickly e.g. Dorset

Concordant coastline - alternating hard + soft rock running parallel to coast so hard rock protects soft rock but if hard rock is breached creates cove e.g. Lulworth Cove

Discordant coastline - alternating layers of hard + soft rock perpendicular to coast + soft rock eroded faster than hard rock so creates headlands + bays along coastline

Storms surge - the pushing of water against a coastline to abnormally high levels, usually a combination of extreme low pressure and high tides

Ocean currents - large scale movement of water in oceans driven by wind + thermohaline circulation

Tidal range - the vertical difference in sea level between high and low tides

Spring tides - tide when moon in line with sun that creates greatest tidal range

Neap tides - when moon at right angle to earth creating lowest tidal range

Longshore drift:

• prevailing wind causes waves to blow in diagonal direction so current is formed perpendicular to shore
• moves sediment down beach in zigzag pattern as swash moves material up beach at angle and backwash takes material back down beach

Rip currents:

• strong, localised + narrow current of water moving away from the shore
• formed when waves break near shoreline, piling up water between the breaking waves and the beach

Upwelling currents:

• winds blowing across the ocean surface push water away from an area
• water rises up from beneath the surface to replace diverging surface water

Tidal/storm surges:

• rise in sea level due to storm + wind
• occurs in areas of low pressure (eye of storm) + higher with larger fetch

High energy coastlines:

• more powerful waves - rate of erosion exceeds rate of deposition
• landforms - headlands, cliffs + wave cut platforms
• steep coastal slope
• more common in cool temperatures with prevailing wind
• e.g. UK west coast from prevailing wind

Low energy coastlines:

• less powerful waves - rate of deposition exceeds rate of erosion
• landforms - beaches, spits, estuaries, inlets, sheltered bays
• found when coastline changes direction with weak winds
• waves spread outwards and energy dissipates - deposition
• e.g. Baltic Sea - enclosed sea area with short fetch

Sources of sediment - rivers, sea bed, wind + cliff erosion

Clastic sediment - smaller pebbles from weathering of rock

Biogenic sedment - skeletons + sediments of marine organisms

Non-cohesive sediment - larger particles such as sand moved grain by grain

Cohesive sediment - small clay + mud particles that band together

Sediment cell:

• stretch of coastline bordered by prominent headlands which contain sediment
• inputs - derived from river, coastal erosion + offshore sources
• transfer(flows) - drift as a result of offshore processes e.g. rip currents
• stores - beach, sand dunes + offshore deposits
• output - material swept out to sea
• positive budget - more material added than removed so shoreline builds
• negative budget  - more material taken away from cell than added so shoreline retreats

Chemical weathering:

• from rain + seawater that react with rock
• carbonation - mixing of water with carbon dioxide to make carbonic acid - reacts with rocks containing calcium carbonate
• oxidation - reaction of oxygen with rock to weaken it when oxidized

Salt weathering - saline (salty) water enters cracks in rocks at high tie, as water evaporates salt crystals form + expand, exerting pressure on rocks

Biological weathering - living organisms contributing to weathering through activity e.g. plant roots growing into cracks in rocks

Physical weathering - break up of rocks not chemical/biological

 Freeze-thaw weathering - when temperatures fluctuate above + below freezing when water enters cracks in rocks + then freezes + expands

Wetting + drying - rocks containing clay get wet so expand

Corrasion - when waves pick up pebbles from seabed which are hurled at cliffs when waves break

Abrasion - when sediment picked up by waves is dragged along shoreline so sandpaper effect

Solution(corrosion) - weak acids in sea dissolve alkali rock

Hydraulic action - when waves advance air trapped and compressed in cracks so when wave retreats compressed air expands and breaks rocks

Attrition - breaking down of rock particles, creating smaller, smoother and rounder stones

Traction - large stones + boulders roll or slide along seabed by seawater in high energy environments

Saltation - small stones bounce along seabed and disrupt other particles

Suspension - small particles picked up by moving water give off murky appearance 

Solution - dissolved materials transported within mass of moving water

Marine Deposition:

• takes place when waves are low energy or when rapid coastal erosion supplies abundant amounts of material

• deposits material where lack of energy from decrease in velocity/water volume

Waves:

• breaking point
• wave steepness
• sea depth
• fetch

Coastline configuration - headlands attract wave energy through refraction

Beaches - dissapate wave energy

Sub-arial processes - rainfall causes mass movement

Types of rock - soft rock more easily destroyed

Human activity - building + sea defences

Headlands + bays - formed along discordant coastlines with hard + soft rock where soft rock eroded more easily

Arch - formed by wearing away of narow headlands often with back to back caves joining

Stack - when top of arch collapses and leaves stand alone rock

Caves - joints and faults in rock are eroded by hydraulic action + abrasion

Wave cut platform - hydraulic action occurs at foot of cliff, a wave cut notch created which grows to become wave cut platform

Cracks - weak rocks such as limestone + chalk are exploited

Stump - when stack collapses

Spits:

• form where coast suddenly changes direction e.g. across river mouth
• longshore drift continues to deposit material across river mouth
• changes to wind direction lead to recurved end + if multiple ends called compound spit
• area behind spit is sheltered + develops into mudflats + saltmarshes

Bars:

• when a spit joins 2 headlands together leaving lagoon behind bar
• also form offshore when partially submerged

Tombolos - when spit joins shore to island or stack

Barrier islands - long, narrow islands of sand parallel + detatched from shore probably formed from sea level rise

Sand dunes - when sand deposited by longshore drift is moved up beach by wind, gets trapped on object e.g. driftwood + vegitation starts to grow so more sand accumulates

Summer:

• steeper
• waves more consructive as energy dissapates + deposits over large area
• swash>backwash
• lower frequency

Winter:

• higher frequency
• erosion from high energy swash
• strong backswash (rip current)

Large pebbles at top of beach - swash of constructive waves

Small pebbles at bottom of beach - weak backwash

Rounded pebbles at bottom of beach - waves causing abrasion + attrition

Inputs:

• beach nourishment 
• cliff erosion
• longshore transport
• onshore transport (swash)

Outputs:

• offshore transport
• human activity
• longshore transport
• storm events

Swash allinged beach - waves break parallel to coast

Drift allinged beach - longshore drift moves material along beach so graded sediment as finer material carried further

Ridges + runnels - ridges + troughs running parallel to the coast formed by deposition during backwash + when water runs back to the ocean

Ripples - small ridges formed on beach when waves + currents flow across loose sand which is piled up

Cusps - semicircular shaped depressions with courser materials around edge formed by waves reaching same point + backwash scouring out finer materials

Berms - series of ridges formed near high tide mark + deposited by swash of constructive waves

Storm beaches - ridge found near back of beach composed of larger sediment deposited by waves during storm events

Rockfall - sudden collapse of individual rock fragments at cliff face from steep conditions with mechanical weathering, causes scree at bottom + inputed into sea

Landslides - block moving rapidly downhill whilst remaining in tact, triggered by earthquakes + heavy rainfall

Runoff - when overland flow occurs, small particles move downslope

Mudflows - earth + mud flows downhill over weak materials such as clay, water gets trapped between rocks + pressure increases

Slumping:

• rainwater soaks into the soil and clay of the cliff, making it heavy
• a slip-plane forms + weight of the saturated clay causes it to slump along this slip plane
• the slump makes a curved movement called a rotational slip

Soil creep/solification - extremely slow movement from when soil particles freeze and unfreeze so expand and contract using freeze thaw

Salt marsh - grass dominated ecosystems where the river meets the sea

Halosere - vegitation succession occuring in a saline environment

Mudflat - created by deposition of fine salts + clays in sheltered, low energy coastal environments such as estuaries

Factors affecting salt marsh development:

• coastal processes e.g. waves
• storm surges
• humans building + eutriphication
• sea level change
• tides
• fluvial processes e.g. discharge + erosion

1. Mud is deposited close to the high tide line, droping out of the water by flocculation when tiny individual partiles of clay/mud stick together so their combined mass sinks to the bed

2. Pioneer plants such as cordgrass start to colonise the transition zone between high + low tides, these are halophytes as can tolerate invasions by salty water + trap further mud deposits

3. Mud levels rise above high tide and lower saltmarsh develops with wider range of plants that no longer need to be so well adapted to salty conditions

4. Soil conditions improve + vegitation succession continues to form a meadow

5. Eventually shrubs + trees colonise the area as succession reaches climactic climax

Threats to salt marshes:

• industrial pollution e.g. oil
• grazing + agricultural use tramples species
• urbanisation
• coastal erosion

Causes:

• ice melt - ice sheets melted from global warming + 2/3rds of freshwater on earth is ice
• isostatic rebound - ice sheets that cover land weigh it down so when ice removed it rebounds
• thermal expansion - global warming causes water to get warmer and expand
• tectonic activity - earthquakes cause coasts to rise

Eustatic changes - change in volume of water in ocean

Isostatic changes - change in land height

Emergent coast - coastline created where there has been a relative fall in sea level e.g. raised beaches

Submergent coast - coastline created from rise in relative sea level e.g. ria

Raised beaches + relict cliffs:

• flat or horizontal surface which is lifted out of the sphere of wave activity above or below current sea level
• emergent coastal landforms such as beaches and wave cut platforms raised above sea level
• e.g. Bay of Biscay, Spain

Rias:

• coastal inlet formed by partial submergence of unglaciated river valley + drowned river valley has clear outline
• e.g. Salcombe, Devon

Fjords:

• long narrow inlet with steep sides or cliff, formed when glacier cuts a u-shaped valley + isostatic rebound occurs
• e.g. Drygalski Fjord, South Georgia

Dalmation coasts: when geology creates valleys parallel to the coast so when when sea level rises, islands remain offshore e.g. Dalmation Coast, Croatia

Predicted sea level rise over 100 years - 18-63 cm but uncertainty as many countries starting to change ways

Impacts:

• increased erosion
• flooding
• re-shaped coastline
• could improve farmland 
• thriving oceans

UK impacts:

• elderly people forced to move
• house prices decrease
• agricultural land affected

Hard engineering - physical change to coastal landscape using resistant materials

Hard engineering techniques:

• sea walls - curved structure that throws waves back into incoming waves with drain oulets
• rock armour (rip rap) - large boulders dumped in front of a cliff/sea wall to take wave force angular to present large surface area, gaps in rock spread energy + boulders shake slightly
• gabions - smaller boulders in steel wire mesh cages to form walls
• revetments - concrete or wooden structures that take wave energy at angle
• groynes - wooden, stone or steel breakwaters at right angles to sea
• cliff fixing - driving iron bars into cliff to stabalise + absorb wave power
• offshore reefs - force waves to break offshore to reduce impact on cliff e.g. redundant ships
• barrages - structure built to act as a dam across an estuary and prevents seawater incursion

Soft engineering - using natural systems for coastal defence

Soft engineering examples:

• beach nourishment - replacing material that has been lost in longshore drift
• dune regenration - replanting areas, restricting access and providing boardwalks to prevent damaged sand dunes
• managed retreat - abandoning the current line of sea defence + letting that land be reclaimed by plants
• land-use management - adressing peoples behaviour and educating
• do nothing - let nature take its course

Shoreline Management Plans:

• introduced in 1995 and based on 22 sediment cells around England
• plan for the short, medium and long term
• provide assesment of risks + framework to adress the risks 
• promotes long term management using 'route plan'
• is sustainable, environemntally acceptable + economically viable
• continually reviewed

Intergrated Coastal Zone Management:

• originated from 1992 UN Earth Summit
• aimed to coordinate management plans
• has a cycle of; information collection, planning, decision making, monitoring + implementation

Dorset coast located on South Coast of England + stretches from Lyme Regis to Bournemouth

Known as Jurrasic Coast due to preserved fossils + in 2001 became a World Heritage Site

Area of erosion around Lulworth Cove containing; Durdle Door (arch), Stair Hole + Old Harry (stack)

Discordant + concordant coastline

Famous features:

• Lulworth Cove - small, circular bay with narrow seaward opening from river eroding weaker rocks behind stone
• Chesil Beach - 18km tombolo connecting to Isle of Portland made up of pebbles + shingle
• Durdle Door - sea arch where sea has broken through outer wall of Portland stone
• Studland Bay - sandy beach stretching for 3 mies with sand dune succession behind know as Studland Heath containing rare wildlife
• Old Harry Rocks - chalk sea stacks eroded by sea

Region in Bangladesh + India on the delta of the Ganges containing mangrove forests

Flat, low-lying land in dynamic equilibrium home to many rare species so protected as national park

Brings opportunities to 4 million people:

• crops such as rice grown in fertile land
• ecosystems of mangrove forest provides fish, crabs, honey + timber for construction or firewood
• protects locals against flooding + coastal erosion
• allow development from wildlife tourism, power plant provides energy + cargo ships transport goods inland

Lack of freshwater as used for irrigation of agricultural land

Growing population - high demand for fuel + agricultural land means mangrove forests removed

Flooding causes salinisation so hard to grow crops

Home to dangerous animals

Lack if employment + income

Low-lying land may not recieve flood warnings

Access difficult so hard to recieve goods, healthcare + education

Resilience:

• Public Health Engineering Department set up to increase acces to clean water + sanitation
• better roads + bridges being built to improve access
• mains electricity extended to more areas
• decreasing poverty + increasing food security
• NGO's offer training in sustainable methods of fishing + farming to prevent environmental damage from poor practices

Mitigation:

• 3,500km of embankments built to prevent flooding
• coastal management projects protect + replant mangrove forests but difficult to prevent illegal forest clearing
  

Adaptation:

• salt-resistant varieties of rice being grown but reduces biodiversity
• projects set up to increase tourism in area which provides jobs + income