coastal systems and landscapes Flashcards
are coasts a closed or open system and define the term
open- both mass and energy are allowed in and out
define inputs and give examples
material/energy moving into the system
tides, waves, sun, air pressure, settlement
define output and give examples
material/energy moving out the system
ocean currents, rip tides, sediment transfer
define stores and give examples
individual parts of a system
beaches, dunes, salt marshes, erosion
define flows/transfers and give examples
links between components
lsd, erosion, transportation, mass movement
define dynamic equilibrium
there is a balance in the system and movement of sediment is contained
define negative feedback loops
changes are counteracted so it remains in a stable, original state
what factors are needed for beaches to exist in dynamic equilibrium
- supply of sand
- change in sea level
- energy of waves
- location of shoreline
define positive feedback loops
one change from the original state triggers an ongoing change which leads it further away from the original
sources of energy in coasts
- wind
- waves
- currents
- tides
what is wind
air moving from high to low air pressure, with larger pressure gradients causing stronger winds
roles of wind
- prevailing wind influences lsd
- creates waves
- fetch
- agent of erosion
define fetch
distance of open water over which a wind blows uninterrupted
how are waves made
wind moves across surface of water, causing frictional drag and creating waves
factors affecting wave energy
- fetch
- wind speed
- wind duration
define swash
water washing up the beach
define backwash
water going straight back down via gravity
features of contructive waves
- low height
- low frequency (6-8 a min)
- long wavelength
- strong swash, weak backwash
- deposits material
- creates a gentle sloping beach
features of destructive waves
- high height
- 10-14 a min
- weak swash, strong backwash
- erodes material
- steeply sloping beach
why do waves break
- waves start out at sea in a circular orbit
- friction slows the base of the waves
- causes orbit to become more elliptical
- top of wave breaks over and crashes onto beach
waves negative feedback loop
- constructive waves build up beach
- encourages destructive waves
- destructive waves moves material back towards the beach
- creates a steep beach profile
- material is removed over time
- encourages constructive waves
define wave refraction
waves break on an irregularly shaped coastline
why is there greater erosion at headlands in wave refraction
wave energy is concentrated here and dissipates to bays
define swash aligned beach
waves break parallel to shore
define drift aligned beach
waves break at an angle to the beach and allows lsd to occur
define wave diffraction
spreading of waves after going through a narrow gap
define currents
permanent or seasonal movement of water in seas and oceans
what factors causes currents
- wind
- variation in water temperature
- variation in salinity
define longshore currents
waves approach the coastline at an angle and the current is parallel to it, transports sediment parallel
define rip currents
strong currents moving away from shoreline between 2 waves
define upwelling
global pattern of currents circulating in oceans can cause deep cold water to move towards surface
define tides
periodic rise and fall of ocean surface
what are tides caused by
gravitational pull of moon and sun and centrifugal force
define spring tides
highest height tide and lowest low tide when sun and moon are aligned
define neap tide
lowest high tide and highest low tide when sun and moon are perpendicular so forced act against
features of high energy coastlines
- high inputs of energy
- large waves
- high rate of erosion
- strong winds
- rocky landforms
features of low energy coastlines
- low energy input
- smaller, gentle waves
- short fetches
- salt marshes and mudflats
- higher rate of deposition
define sediment cell
stretch of coastline, usually bordered by prominent headlands, where movement of sediment is contained
examples of sediment sources
- river- 90% of coastal sediment
- cliff erosion
- lsd
- glaciers
- offshore
define sediment budget and the different types
balance between sediment being added and removed from coastal system
positive budget= more sediment added then removed so shoreline builds to sea
negative budget= more sediment removed then added so shoreline recedes
erosion processes
- hydraulic action
- wave quarrying
- abrasion
- attrition
- solution
define hydraulic action
waves crash onto cliff face and air is forces into cracks and the high pressure causes the cracks to force apart
define cavitation
bubbles found within the water may implode under high pressure creating tiny jets of water that erode the rock
define wave quarrying
waves break on cliff face and exerts a pressure which directly pull away rocks from cliff face
define abrasion
sediment is picked up by the sea and hurled at the cliff to rub in a sandpaper action
define attrition
rocks rub against each other and become smaller and rounder
define solution
mildly acidic seawater can cause alkaline rocks like limestone to be eeoded
factors affecting erosion
- human activity
- geology
- bathymetry of sea bed
- size of fetch
- frequency of storm events
- amounts of weathering
- strength of wind
- landforms
- geological structure of coastline
how are headlands and bays made
discordant coastline where differential erosion occurs, wave refraction focus on headlands and energy is dissipated towards bays where deposition creates beaches
process of wave cut platforms
- high waves concentrate erosion at base of cliff
- cliff is undercut forming a wave cut notch
- undercut cliff collapses and cliff retreats
negative feedback of wave cut platform
eventually waves can out reach the cliff which reduces erosion or base is too wide so erosive power isn’t strong enough so rage of retreat slows
process of CASS
- cracks in resistant rock are eroded by hydraulic action or abrasion and widens into cave
- erosion focuses more on the headland and opens into an arch
- weathering weakens the top snd erosion creates a wave cut platform which makes it collapse into a stack
- sea attacks the base and a wave cut notch will undercut the stack and will be left as a stump
what is a geo
narrow and deep cleft in the cliff face with erosion on lines of weakness to make long, narrow sides
what’s the blowholes
sea caves get punctured and water blasts upwards
define weathering and the 3 different types
breakdown of rocks over time, weakening it and making it more susceptible to erosion
physical/mechanical, chemical, biological
negative feedback with weathering
removal of weathered rock is slower than rage of weathering which will lead to a buildup of debris at the base, which protected the cliff from erosion and weathering
positive feedback of weathering
rate of removal of rock is faster than rage of weathering, so the cliff is more exposed to erosion and more weathering
examples of mechanical weathering
freeze-thaw weathering- water enters a crack in the rock and over time freezes and melts, which expands the volume by 10% and weakens it
salt crystallisation- salt water evaporates and leaves salt crystals behind which expands cracks in rock or corrode rock like iron
wetting and drying- rocks rich in clay expand when wet and contract when dry
examples of chemical weathering
carbonation- rainwater absorbs CO2 from sir to form weak carbonic acid which reacts with calcium carbonate in rock to form calcium bicarbonate which is easily dissolved
oxidation- reaction of mineral with oxygen e.g iron rusting
solution- dissolving of rock minerals
hydration- physical addition of water to minerals which makes them more susceptible to chemical weathering
hydrolysis- mildly acidic water reacts with minerals
examples of biological weathering
- plants roots grow in the cracks and widen them
- water running through decaying vegetation becomes acidic and leads to increased chemical weathering
define mass movement
movement of large amounts of land
factors dependent on the type of mass movement
- slope
- geology
- vegetation
- saturation of ground
- temperature
what is soil creep
extremely slow form of movement of individual soil particles as particles rise and fall due to wetting and drying and respond to gravity downwards
what is a landslide
large block of land moves down cliff face very quickly due to heavy rainfall getting between the joints and bedding planes which reduces friction
what are mudflows
earth and mud flowing downhill over unconsolidated or weak bedrock (clay) as water gets trapped and increases pore water pressure and forces rock particles apart
what is rockfall
sudden collapse of breaking away of individual, resistant rock fragments down a steep cliff, when exposed to mechanical weathering or earthquakes and form scree as a temporary store
what is slumping
slide surface is curved and wears unconsolidated clays causes land to collapse under its own weight
what is run off
overland flow occurs down a slope and small particles and water are moved downslope into littoral slope
what is solifluction
surface level of soil thaws and becomes extremely saturated cashing it to slide down the permafrost
processes of transportation
traction- large boulders roll along the seabed
saltation- smalls tones bounce along the seabed
suspension- very small particles carried in moving water
solution- dissolved materials being transported in moving water
what is longshore drift
movement of sediment along the beach at the angle of the prevailing wind, where swash loves material up and backwash moves it back down via gravity
processes of deposition
gravity settling-waters velocity decreases so sediment starts to become deposited
flocculation- clay particles clump together due to chemical attraction and then sink due to high density
features of besches
- stretch from high to low tide line
- created when waves lose their energy and deposit material
- sand provides beaches with a gentle gradient (less than 5 degrees)
- shingle provides steeper gradients of around 10-20 degrees
define ridges and runnels
ridges and troughs running parallel to the coast near the low water mark
define ripples
small elongated ridges
define cusps
semicircular shaped depressions with coarser material around the edge
define berms
series of ridges that run the length of the beach and form near the high tide mark
define storm beach
ridge found near the back of the beach composed of larger sediment
formation of a spit
- prevailing wind moves sediment via lsd
- when coastline changed the momentum continues carrying sediment out to sea
- salt marsh develop behind made up of halophytes and vegetation helps stabilise the land
- hooks can form when prevailing wind changes
- spit stops when river estuary cuts it off
difference between simple and compound spit
simple spit is straight whereas compound spit has hooks
define tombolo
sand and shingle connecting the mainland to an island
how can tombolos form
- lsd
- marine transgression where sand and shingle migrate gradually onshore
- wave refraction and diffraction
define offshore bar
semi-submerged rushes of sand created offshore from the coast
how are offshore bars formed
- waves break too early
- destructive waves erode the sand from beach and deposit offshore
define barrier besch
spit develops and joins two parts of coastline with lagoon behind
how are barrier beaches formed
- marine transgression when sea levels rise and gradually pushes sediment towards the coastline
- lsd over areas of water like bays
define barrier island
bar detached from mainland
how are barrier islands formed
proximal energy (where spit no longer meets coastline) has been breached and detached to create an island
define eustatic sea level change
global change in sea level due to rise or fall in the level of the sea itself
how does eustatic sea level change work
- if the climate warms then the ice caps melt and sea levels rise, but if the climate cools then ice builds back up and sea levels fall
- thermal expansion and contraction refers to water expanding when getting warmer, which increase the volume
- positive feedback loop as ice has a high albedo (reflection of sunlight) and as this melts it exposed more land which increases temperature so more ice melts etc
define isostatic sea level change
local change in sea level due to land rising or falling relative to the sea
how does isostatic change affect sea level rise
glaciation pushes land downwards and allows the land to sink relative to the sea and the water moves up
define isostatic rebound
when the land springs back up due to glaciers melting, causing a see-saw effect
like scotland and northwest rising and south subsiding
define tectonic sea level change
tectonic hazards along plate boundsries cause land subsidence which leads to isostatic sea level rise
define halosere
succession in saline environments
define psammosere
succession of plants on sand
define slacks
small bodies of water that reach down to the water table and are high in biodiversity
define blowouts
sand dunes that have had their vegetation cover destroyed by grazing animals or human activity
define mudflats
deposition of fine silts and clays in sheltered low energy environments like estuaries
sand dune formation
- object to trap sediment and allow sand to accumulate around
- pioneer plants like prickly seawort will stabilise the land to create an embryo dune
- sea gets pushed back as land rises and allows space for a new embryo dune to grow
- more sand accumulates and allows the dune to grow into a fore dune with plants like marram grass
- plants will die and leave humus to grow new plants
- biodiversity increases and turns into yellow dune
- then grey dune with sea buckthorn
- slacks
- mature dune with trees
development of salt marshes
- mud and other fine material begin to accumulate in a coastal region as they are deposited by flocculations
- pioneer halophytes like spartina begin to develop and trap mud
- more mud accumulates and gets thicker and new species grow like marsh grass and sea lavender
- larger species slow the current and add humus
- land starts to rise in mud and an area no longer inundated by salt water can grow reeds and rushes
- hollows may form where sea water gets trapped then evaporates
define submerging coastal landforms
when sea level rises or land sinks
define fjords
long narrow arm of sea formed from a submerged u shaped valley
how are fjords formed
- u shaped valleys are created from the erosive power of glaciers, eroding sides and bottom
- when the glaciers melt it will cause eustatic sea level rise and flood the valley
- deeper in the middle section as terminal moraine is where material was deposited at the end of glacier
define rias and how are they formed
drowned river valleys with a dendritic pattern when rising sea levels down the valleys of rivers
define dalmations coasts
submerged river valleys parallel to the sea and make the top or hills look like islands
define emerging coastal landforms
landforms when sea level falls or land rises
define raised beach
beaches and cliff lines elevate above sea level and expose a new storm beach, features it cliffs like wave cut platforms, CASS but are no longer eroded or affected by the sea
define relict cliff
back of raised beach with a steep slip displaying evidence that they used to the eroded
define marine platform
expanse of gently sloping, formerly submerged land has been exposed by uplift or fall of sea level
define coastal management
response to the natural and human activities that threaten coastal environments
aims of coastal management
- defend and mitigate against the impacts of flooding
- proceed against the effects of lsd
- stabilise sand dunes
- protect estuarine landscapes and ecosystem
- protect and mitigate against the impacts of coastal erosion
define hold the line
retain the existing coastline by maintaining the current defences or building new ones
define advance the line
build new defences seward of the existing line
define retreat the line
actively manage the rate and process by which the coast’s retreat
define do nothing but monitor
let the area erode when it is not economically or environmentally viable to undertake defences
define hard engineering and name the techniques
building artificial structure to reduce or stop the impacts of coastal processes
groynes, sea walls, rock armour, gabions, cliff fixing, offshore reef, barrage, revetments
what are groynes and evaluation
wooden, rock or steel structures going out into sea to help trap sediment being moved by lsd
+ work with natural processes to build up the beach, not too expensive
- starve beaches of fresh sediment further up the beach, unnatural, unattractive
what are sea walls and evaluation
recurved face to reflect waves back to sea and dissipate wave energy
+ effective, often have promenade to walk along
- reflect wave energy instead of absorb, instructive and unnatural, expensive
what is rock armour and evaluation
large rocks at the foot of cliff or top of beach to be a permeable barrier to the sea and breaking up the wave
+ cheap, easy to construct, often used for recreation like fishing
- intrusive, rocks are imported, dangerous
what are gabions and evaluation
steel wire cages filled with rocks to absorb wave energy
+ strong, flexible, cost effective
- ugly, dangerous for people and animals
what is cliff fixing and evaluation
driving metal bars into the cliff face to stabilise and absorb wave power
+ simple, cost effective
- natural sediment transport disrupted, requires maintenance
what is offshore reef and evaluation
partly submerged rock designed to break up waves before reaching coastline
+ effective permeable barrier, does not construct
- unappealing, navigation hazard
what is barrage and evaluation
moveable flood barrier and acts as a dam
+ no pollution, reliable
- presents free access if boats, spoils view, destroys habitat, very expensive
what are revetments and evaluation
concrete or wooden structures placed along a coastline to absorb wave energy
+ cost effective
- unappealing, need constant maintenance
define soft engineering and give examples
natural defences that work with the environment
beach replenishment, manages retreat, dune regeneration, marsh creation, beach reprofiling, cliff regrading and drainage
define beach replenishment/nourishment and evaluation
replacement of sand lost through lsd
+ wider beaches, cheap, natural
- taking material from other beaches, has to be replenished frequently, dreading may have consequences
define managed retreat
abandoning current sea defences and management of exposed land
define dune regeneration and evaluation
stabilisation of dunes by planting vegetation like marram grass
+ maintains natural environment, creates wildlife habitats, cheap
- time consuming, people may ignore
define marsh creation and evaluation
realignment of coast by creating salt marshes to absorb wave energy
+ vegetation stabilised mudflats and helps to reduce the energy of the waves, creates new habitats
- not useful when erosion rates are high, expensive
define beach reprofiling and evaluation
artificial reshaping of a beach using existing beach material
+ natural
- steep beaches are unnatural, expensive
define cliff regrading drainage and evaluation
reduces angle of the cliff to help stabilise it and drainage removed water to prevent landslides
+ cheap, effective in clay or loose rock
- can dry out if too much, may cause cliff to retreat
wallasea island managed retreat case study
- 300m section of a sea wall breached to create a marine wetland
- 115 hectares flooded
- £7.5m government funded project to replace bird habitats, improve flood defences, and create new leisure opportunities
define and features of integrated coastal zone management
aims for coordinated application of coastal strategies to meet all needs
- recognises importance of coastland the different people’s activities that need to be protected
- must be sustainable
- involve all stakeholders
- dynamic strategy- changing with environmental changes
define and features of shoreline management plans
strategy on how to manage different areas between sediment cells
- either hold the line, advance the line, managed retreat, or do nothing
- all the local authorities in one sediment cell cooperate to come up with a SMP
- 22 SMPs set up in england and wales
- short medium or long term
- assess risks and provide policy agenda for protecting a coastline
background of the Sundarbans
- occupies 10,000km^2 of Southern Bangladesh and India
- coastal zone occupying the worlds largest delta
- created by depositor from the rivers Ganges, Brahmaputra and Meghna
- tidal action forms deep water channels and cuts new ones
- largest mangrove forest- shrubs or small trees that grow in coastal saline or brackish water
- home to rare species of plants and animals like bengal tigers and Irawadi dolphins
opportunities in the Sundarbans
- natural products like timber, poles, charcoal, synthetic fibres
- fertile land for growing crops
- fish, crabs, honey, vinegar
- mangrove is a natural defence against flooding by absorbing excess water
- opportunities for development with ecotourism and power plant to provide energy
natural challenges in sundarbans
- coastal flooding
- cyclones
- high levels of salinity in soil
- instability of the islands
– accessibility and remoteness
– human eating tigers
human challenges in sundarbans
- over exploitation of coastal resources
- conversion of wetlands to intensive agriculture
– destructive fishing techniques
– lack of awareness of environmental and economic importance of the region
– resource use conflict
– lack of awareness of coastal issues by decisionmakers
– lack of freshwater as it is a diverted upstream for irrigation
– lack of employment and income opportunities
– 42% of population below poverty
– 2014 oil tanker southern star seven was anchored in the river and capsized
resilience responses in sundarbans
- public health engineering development increasing access to clean water and sanitation
- better roads and bridges
- mains electricity will be extended to more areas and solar panels in remote areas so flood warnings can reach communities
– oxfam GB provide farming subsidies to increase food production and provide jobs
– NGOs like USAID are offering training in sustainable methods of fishing and farming
– Dhaka Ahsania Mission provided 500 households with training on income generation activities, 130 with sanitary products, 18 deep tube wells for safe water and 450 fuel efficient low carbon emitting oven
mitigation responses in the sundarbans
- 3500 km of embankments to prevent flooding
– coastal management to protect existing mangroves and replant areas that have been removed
– mitigate against extreme events like cyclones by funding for cyclone shelters and early warning systems.
– 2012 Bangladesh government declared 3 zones of major canals in Sundarbans as dolphin sanctuaries and fishing is prohibited - Bangladesh ICZM in 2005 to protect population, environment, freshwater resources and improve economic
opportunities
adaptation responses in the Sundarbans
- salt resistant varieties of rice
– mangrove eco-Village near Pasur River – popular for dolphins. - building houses on stilts to protect from flooding
– non-intensive farming practices
opportunities for sustainable development in the Sundarbans
2011- a memorandum of understanding between Bangladesh and India, for conservation of Sundarabans – management of tigers and fisheries
background and features at porlock bay
- high energy coastline
- shingle beach
- 2 headlands of quartzite with soft mudstone- discordant coastline
- periglacial area due to it being at the end of a glacier - lots of freeze thaw weathering and solifluction which brings shattered rock downslope
- ## wave refraction as waves come from NW due to refracting around SW England
management at porlock bay
- groynes to protect porlock weir
- hurlstone point is SSI- lsd material travels here
- sea wall
- after 1996 storm breach, local area decided to compensate farmers and allow for managed retreat and development of saltmarsh
