Coastal systems and landscapes Flashcards
Mass movement
The downslope movement of material under the force of gravity
Factors impacting mass movement
- Level of cohesion within the sediment
- Height of the slope and slope angle
- Grain size within the sediment
- Temperature and level of saturation
Types of mass movement
Landslides
Rock falls
Mudflows
Rotational slip/slumping
Soil creep
Landslides
Cliffs with softer rock or deposited material slipping as a result of failure when lubricated
- Usually follows heavy rainfall
Rock falls
Cliffs undercut by the sea or on the slopes affected by mechanical weathering like frost action causing the falling of rocks to happen
Mudflows
Heavy rainfall causing large quantities of fine material to flow downhill, the soil then becomes saturated and so if excess water cannot percolate deeper into the ground the surface layers become very fluid and so flow donwhill
- Flow dependant on level of saturated, sediment type and slope angle
Rotational slip/slumping
Softer material overlying more resistant materials and so subjecting the cliff to slumping. With excessive lubrication, whole sections of the cliff may move downwards with a concave slide plane producing a rotational slip
-Common feature of British coasts like East Yorkshire
Soil creep
Slow, almost imperceptible continuous movement of individual soil particles downslope
- Influence from soil moisture and weathering
Marine erosion
Erosion refers to the wearing away of the land surface and removal of materials by river and seawater, ice and wind.
Hydraulic action
The impact on rocks by the sheer force of water (without debris) exerting enormous pressure upon a rock surface and so weakening it
Wave quarrying
A breaking wave trapping air as it hits a cliff face, this force of water compressing the air into any gap in the rock face creating enormous pressure within fissure/joint . Water then pulls back leaving an explosive effect of air under pressure being released weakening cliff face.
Abrasion / corrasion
Material the sea has picked up also wearing away rock faces by being hurled against cliff face (also apparent on inter-tidal rick platforms)
Attrition
Rocks in the sea carrying out abrasion are slowly worn down into smaller and more rounded pieces.
Solution
Materials in the sea being dissolved into the water (calcium based rocks)
Also the effects of evaporation of salts from water in the rocks to produce crystals.
Backshore
Area between high water mark and and the landward limit of marine activity
-changes here only normally take place during storm activity
Nearshore
The area extending seaward from the high water mark to the area where waves begin to break
-includes swash zone, surf zone, breaker zone
Foreshore
The area lying between high water mark and the low water mark
-most important zone for marine processes in times that aren’t influenced by storms
Inshore
The area between low water mark and the point where waves cease to have any influence on the land beneath them
Offshore
The area beyond the point where waves cease to impact upon the seabed and in which activity is limited to deposition of sediments
Inputs of coastal systems and landscapes
- wind,wave,tides,sea currents
- sediment
- geology of coastline
- sea level change
Outputs of coastal systems and landscapes
- dissipation of wave energy
- accumulation of sediment above the tidal limit
- sediment removed beyond local sediment cells
Marine transportation
The movement of sediment, water and other materials through the ocean and coastal areas by wave and tidal energy
Traction
Large stones and boulders rolled and slid along the seabed and beach by moving seawater in high energy environments
Saltation
Small stones bouncing along the seabed and beach typically assoicated with relatively high energy environments
Suspension
Very small particles of sand and silt being carried along by the moving water. This material can also be picked up through turbulence existing in the water
Solution
Dissolved materials transported within the mass of the moving water
Longshore drift
Movement of sediment along a coastline in a zigzag
- Swash brings sediments onto the shore in the direction of the prevailing wind
- Backwash drags sediment out to sea in a straight line due to gravity
- Over time this transports sediment along a coastline
(larger sediment travels the least because they require more energy, small fine sediment travels further as they need less energy)
Fetch
Distance wind has travelled
Factors in wind energy
- strength of the wind
- duration
- fetch
Weathering
The breakdown/ decay of rock near or at the Earth’s surface creating regolith that remains in situ until is moved by erosional processes
Types of weathering
- Mechanical
- Biological
- Chemical
Biological weathering
Processes that lead to the breakdown of rocks by the action of vegetation and coastal organisms
Mechanical weathering
Freeze thaw wea
Sub aerial processes
Land-based processes occurring above the waterline.
Key features of a wave
Wave height
Wavelength
Wave frequency
Wavelength
Distance between successive crests
Wave height / amplitude
Height difference between wave crest and trough
Wave period
Time between one crest and following crest passing a fixed point
Backwash
Action of water receding back down the beach towards the sea
Swash
Rush of water up the beach after a wave breaks
Low energy coasts
- Low wave energy
- Rate of deposition exceeds rate of erosion
(Baltic Sea has sheltered waters and a low tidal range)
High energy coasts
- High wave energy by strong, steady prevailing winds
- Rate of erosion exceeds rate of deposition
(exposed Atlantic coasts, Cornish coast)
Coastal sediment budget
The balance between sediment being added to and removed from the coastal system
Sediment cell
A distinct area of coastline separated from other areas by well defined boundaries like headlands and stretches of deep water
- A closed system
Longest fetch in the UK
Extends over 3000miles from Brazil in the South West which coincides with the direction of the prevailing wind, accounting for the high energy waves that affect the South-West coast e.g. Cornwall
Wave trough
Lowest point of the wave
Constructive waves characteristics
- Long wave length
- Low amplitude / wave height
- Stronger swash than backwash
- Longer wave period
- Low frequency (6-8min)
Destructive waves characteristics
- High amplitude / wave height
- High frequency (10-14min)
- Stronger backwash than swash
- Short wave length
- Shorter wave period
What do destructive waves form?
Storm beach
- Force of each wave projecting shingle towards rear of beach forming large ridges
What do constructive waves form?
Berms
- Material is slowly but constantly moved up to beach by insufficient force to pull sediment off beach forming ridges
Definition of wave refraction
The distortion of wave fronts as they
approach an indented shoreline
Wave refraction explanation
When waves approach a coastline that is not a regular shape, they are refracted and become increasingly parallel to the coastline. The result of this is energy becomes concentrated at headlands and dissipated in bays. This accounts for the presence of erosive features at headlands
(cliffs, stacks) and deposition features in bays (beaches).
Tides
Periodic rise and fall of the level of the sea in response to the gravitational pull of the Sun and Moon
Currents
Permanent or seasonal movement of surface water in the seas and oceans
Spring tides
Twice in a lunar month the Earth, moon and sun are in a straight line producing the highest monthly tidal range.
Neap tides
Twice a month the sun is positioned 90 degrees from each other giving the lowest tidal range. (10-30% lower than average)
Impacts that tides can have
- Determine the upper and lower limits of erosion and deposition
- Amount of time each day that the littoral zone is exposed and open to sub-aerial weathering
Evidence of tidal range influence around the world
- Medittarean Sea has low tidal ranges restricting action to a narrow width in coastal zone
- British Isles has high tidal ranges giving a wide zone of attack resulting in the formation of wave cut platforms
Tidal surges
Meteorological conditions giving rise to strong winds producing higher water levels than those at high tides.
- North Sea affected by this
(surges in 1953, 2013, 2014)
Where does coastal sediment come from?
- Streams / rivers
- Estuaries
- Cliff erosion
- Offshore sand banks
- Material from a biological origin (shells, coral fragments, skeletons of marine organisms)
Sediment cells division
Larger sediment cells divided into smaller sections, sub cells, to allow closer management and study
Factors affecting coastal eorision
- Wave steepness and breaking point
- Fetch
- Sea depth
- Coastal configuration
- Beach presence
- Human activity
How many sediment cells in England and Wales
11 sediment cells have been identified
Example of a sub cell
Christchurch Bay in Dorset
Run off
Heavy rain washes material from the surface of a cliff over the edge and down onto the shore
- Stream emerging in a bay
- Stream cascading over a cliff
Thermohaline circulation
The transportation of ocean water around the world driven by saline and temperature.
Causes of deposition
- Source of energy altering
- Changes in flow direction
- Interruptions to flow
- Increased load
- Increased friction
Factors affecting coastal erosion
- Geology of coastline rock
- Wave energy
- Human Influence
- Presence/absence of beach
- Sub aerial processes
- Frequency of storm events
- Topography
What is a spit?
A spit is a long, narrow beach of sand or shingle with one end attached to the shore and the other extending into the sea or estuary.
Characteristics of a simple spit
- Simple spits are either straight or recurved.
- Do not have minor spits or recurved ridges, along their landward edge.
Characteristics of a compound spit
- Compound spits may have similar features to simple spits.
- Have a number of recurved ridges or mini spits.
Types of spits
Simple spits
Compound spits
What is the proximal point?
Where the spit joins to the mainland
What is the distal point?
The furthest point of the spit that extends from the headland
Example of a spit
Spurn Head Holderness Coast
Example of a tombolo
Chesil Beach Dorset Coast
Example of a bar
Slapton Sands Devon
What is a barrier island?
A long, thin, sandy stretch of land, oriented parallel to the mainland coast that protects the coast from the full force of powerful storm waves. Between the barrier island and the mainland is a calm, protectedwaterbody such as a lagoon or bay.
Formation of a barrier island
Barrier islands may have formed when low-lying areas of spits, extensions of beaches that protrude into a bay as a result of deposition of sediment carried by longshore currents, were breached by the sea.
Example of a barrier island
Scolt Head, Norfolk
Formation of a tombolo
Where a spit forms on a coastline where there is a small offshore island, the ridge of beach sediment is deposited towards the small island, and so a Tombolo is formed. This occurs when the ridge of sediment attaches the original coastline to the offshore island.
Formation of a bar
If a spit develops across a bay where there is no strong flow of water from the landward side, it is possible for the sediment to reach across to the other side. In this case, the feature is known as a bar.
Some bars may be the revealing of offshore material following the last ice age, as sea levels rose. Slapton Ley, a bar formed in Devon, is believed to have been formed in this way
Micro features of a beach
Ridges and runnels, ripples, cusps, berms, storm beaches
Inputs of sediment
Beach nourishment, fluvial sediment, longshore transport, swash, cliff and dune erosion
Outputs of sediment
Backwash, sand mining, longshore transport, storm events, wind transport
Characteristics of beaches
- Occur along coast between low and high tide
- Shaped by swash and backwash as well as longshore drift processes
- Sand produces gentle gradient beaches ( <5)
- Shingle produces steeper gradient beaches (10-20)
Ridges and runnels
- Run parallel to coast near low water mark
- Ridges formed by deposition (backwash) and runnels formed by water returning to ocean
- Broken down by drainage channels
Ripples
- Relatively small, elongated ridges
- Waves and current flow across loose sand that is dragged along bottom piling up
Cusps
- Semicircular shaped depressions with coarser material around edge and finer material in middle
- Formed by collection of waves reaching same point and backwash scoring out finer material
What is an emergent coast?
A coastline exhibiting features associated with falling sea levels e.g. raised
beaches and relict cliffs.
- They begin to appear towards the end of an ice
age and they occur when isostatic rebound takes place faster
than a eustatic rise in sea level.
What is a submergent coast?
A coastline exhibiting features associated with rising sea levels e.g. Rias and Fjords.
- They form when the eustatic rise in sea level
takes place faster than the isostatic rebound after an ice age.
Rias landform
This is a drowned river valley. As sea levels rise they flood the river valleys, leaving only the high land visible.
- Kingsbridge Estuary in South Devon
Fjords landform
This is a drowned glacial valley. As sea levels rise, U-shaped valleys left by glaciers are submerged.
Dalmation coasts
Dalmatian coasts form in areas of the world where valleys
(especially glacial valleys) lie parallel to each other. When the
valleys are flooded by the rise in sea level, the tops of the
valleys remain above the surface of the sea and appear to be a
series of islands that run parallel to the coastline.
- Dalmatian coastline of Croatia in the Adriatic Sea
Relict cliffs
Wherever land has risen from the sea in the past as a result of isostatic processes, degraded cliffs can often be seen that are no longer reached by the sea.
Instead of boasting a dramatic near-vertical profile, gentle vegetated slopes are apparent on account of marine erosion no longer attacking and undermining the landform.
- Fife, Scotland
Raised beaches
Areas of former wave-cut platforms and their beaches which are at a higher level than the present sea level due to eustatic changes.
- Drumadoon, Isle of Aaron
Eustatic change
A global change in sea level resulting from an actual fall or rise in the level of the sea itself.
Global warming is increasing sea levels.
– This is due to thermal expansion as water gets
warmer
It is also due to melting of freshwater ice sheets, e.g. Greenland
Isostatic change
Local changes in sea level resulting from the land rising or falling relative to the sea, occurring much slowly than eustatic change.
- When large ice sheets cover the land it weighs down the land and actually makes it sink.
- When the ice melts the land begins to rise as the weight is removed
Tectonic change
The rise or fall in sea level resulting from tectonic processes.
Hard engineering
Making a physical change to the coastal landscape using resistant materials, like concrete, boulders, wood and metal.
Soft engineering
Using natural systems for coastal defence, such as beaches, dunes and salt marshes, which absorb and adjust to wave and tide energy.
Hard engineering
- Sea walls
- Aim to dissipate wave energy. The recurved structure throws waves back out to sea into the path of the next incoming wave, reducing its wave impact
- They also provide a physical barrier to flooding by raising the height of the coastline and must have a continuous facing because any slight gap will be exploited by waves
- Drain outlets so that any water that does get over them does not accumulate inland
Vancouver Seawall, Canada
Hard engineering
- Rock armour
- Consists of large boulders placed in front of a cliff or sea wall to take the full force of the waves
- The boulders are deliberately left angular in appearance to present a large surface area to the waves and create gaps for water to filter through, to mitigate their impact on the coast
- Usually the boulders are not secured in place, so energy is taken out of the most powerful waves by rocking or slightly being moved
Port of Sunderland, 400m distance
Hard engineering
- Gabions
- Operate on the same principle as rip-raps
- Smaller boulders are contained within steel wire mesh cages, each of which can be joined together to form larger structures or walls
Seaton Beach, Devon
Hard engineering
- Revetments
Concrete or wooden structures placed across a beach or coastline to take the full force of the wave energy, preventing further erosion of the coast
Stolford beach, Somerset
Hard engineering
- Groynes
- Wooden, stone or steel breakwaters built nearly at right angles to waves (usually 5 to 10° from the perpendicular to prevent scouring on the down-drift side)
- Built to control longshore drift by trapping sediment to create higher and wider beaches which will then also dissipate wave energy
- Break up the waves as they hit the coast
- Halting the bulk of longshore drift in an area may have serious effects down the coast where it will cut off the supply of beach material and could leave the coast there exposed to erosion.
Bournemouth groynes
Hard engineering
- Cliff fixing
- Often done by driving metal bars into the cliff face, both to stabilise it and to absorb some wave power
Canford Cliffs, Dorset
Hard engineering
- Offshore reefs
- Force the waves to break offshore, which reduces their impact on the base of cliffs
- Sometimes redundant ships have been deliberately sunk parallel to the shore to both slow down approaching waves and to act as a substructure for reef material to begin to colonise
Portland Harbour
Hard engineering
- Barrages
- Large structures built to prevent flooding on major estuaries and other large sea inlets
-They act as a dam across an estuary and prevent incursion of seawater
The Cardiff Bay barrage in Wales, completed in 1999
Disadvantages of hard engineering
- structures can be expensive to build and to maintain
(to build a sea wall can cost over £7,000/m) - defence in one place can have serious consequences for another area of the coast
- structures are sometimes an eyesore, spoiling the landscape and physically disrupting natural habitats.
Advantages of hard engineering
- If very well kept, they can operate for 40 years
- The structure is neat and straightforward to develop. It very well may be built in weeks instead of months, lessening the monetary effect of its establishment.
Soft engineering
- Beach nourishment
- Aims to replace material that has been lost through longshore drift
- Local councils may move material from one end of a beach to the other before the start of the tourist season
7m beach nourishment scheme to protect thousands of properties and businesses in Lincolnshire.
Soft engineering
- Dune regeneration
- Replanting vulnerable areas with plants such as marram grass and stabilising the surface with sacking or wire mesh
- Afforestation with quick-growing conifers
- Selective grazing
- Restricting access by fencing off areas
- Providing boardwalks for tourists
- Giving tourists information about potential damage
Fylde coast, Lancashire
Human impacts on sand dunes
Fragile sand dune environments are easily disrupted by human activities
- Most damage is caused by the removal of vegetation by agriculture (overgrazing) or tourism (trampling the dunes). This can lead to blowouts where large amounts of sand may be carried inland and deposited on valuable agricultural land
Soft engineering
- Managed retreat
- Abandoning the current line of sea defences and developing the exposed land in some way, perhaps with salt marshes, to reduce wave power
- Low-lying land will be flooded, reclaimed naturally by marsh plants. The new area of marsh will act as a defence against rising sea levels
- Scale of hard engineering sea defences can be reduced
- There have been proposals in some areas to ban new developments on the coast.
California USA, requirements on some stretches of coastline that buildings must be a certain distance from the shore
Soft engineering
- Land use management
- It involves addressing people’s behaviour and educating the local community
- Officials help people plan for the future by encouraging landowners to think about how they can continue to use land that is at risk.
- Giving land at risk of flooding over to grazing rather than growing crops means the sheep or cattle can be moved if storms are forecast
- It only works if the local population agree to having their use of land limited, and it cannot remedy damage that has already been done
Lyme Regis, UK
Soft engineering
- Do nothing
- Hundreds of millions of pounds are spent annually in the UK on coastal protection. It might be cheaper to let nature take its course and pay compensation to those affected
- Some argue that the limited funds available for coastal protection should be targeted to places that have significant infrastructural or economic value for large numbers of people
-This debate is not new; the House of Commons Select Committee on Agriculture suggested in 1998 that large tracts of land should be ‘surrendered to the sea’ as trying to protect them is a waste of money
Aims of coastal management
- To provide defence against, and mitigate the impacts of flooding
- To provide protection against, and mitigate the impacts of coastal erosion.
- Stabilising beaches affected by longshore drift
- Stabilising sand dune areas
- Protecting fragile estuarine landscapes
Integrated coastal zone management
(ICZM)
- originated from the UN Earth Summit of
Rio de Janeiro in 1992
Initiative backgrounds
● coastal zones are some of the most ecologically productive areas in the world
● the natural assets of coasts have for millennia made them popular for:
– settlements
– tourist destinations
- business centres
– ports
● around 200 million people live near Europe’s coastline
Integrated coastal zone management
(ICZM) Rio
Impacts
Cconcentration of people and economic activity is putting great pressure on our coastal environment and creates excessive
exploitation of natural resources, all of which is leading to:
● biodiversity loss
● habitat destruction
● pollution
● conflicts between stakeholders
● overcrowding in some locations.
