1
Q
What is coastal system made up of
A
- inputs
- flows/ transfers
- stores & components
- outputs
- feedbacks
2
Q
Inputs
A
- things that enter the system from outside sources/systems
EXAMPLES - wind
- fluvial (river based) sediment
- precipitation
- ocean currents
3
Q
Flows/transfers
A
- process of movement within a system
EXAMPLES - erosion
- LSD
- mass movement
4
Q
Stores/components
A
- parts of the system not necessarily in motion
EXAMPLES - beaches
- bars
- spits
- sand dunes
5
Q
Outputs
A
- material/energy moving out of a system
EXAMPLES - wave cut platforms
- bays
- headlands
- evaporation
- rip tides
6
Q
Factors influencing he coastline
A
- terrestrial (tectonics, supply of sediment, fluvial processes, industrial + residential development)
- Marine processes (wave shape/size, biotic features, sea level change, wave direction, glaciations)
- human intervention (sea defences, pollution, purism + recreation, industrial + residential development, sea level rise, conservation
- atmospheric 9global warming, fetch, winds, precipitation, temperature, sub-aerial processes, solar energy)
7
Q
Sources of energy (what its caused by*)
A
- wind (high and low air pressure)
- waves (wind, friction)
- currents
- tides (the moon, sun, gravity)
8
Q
Wind energy
A
- formed by air moving between areas of different pressure (from high to low) along a pressure gradient
- low pressure: air is rising (heated)
- high pressure: air is sinking (cooled)
- the steeper the gradient the faster the wind moves. So areas with large pressure gradients experience strongest winds
9
Q
Formation of waves
A
- created by energy passing through water, causing it to move in a circular motion. However, water does not actually travel on waves. Waves transmit energy, not water. Waves are most commonly caused by wind: wind-driven waves are created by frictional drag between wind and surface water. As wind blows across the whole ocean surface the continual disturbance forms a wave crest. As the wave approaches the shore, disturbance to the circular motion beneath the surface leads to more horizontal wave movement and wave breaks
10
Q
Why are some areas subject to powerful waves and some aren’t
A
Prevailing wind direction -> SW in England
11
Q
Constructive waves
A
- strong swash & weak backwash
- add material along the coastline
- low wave with long wavelength
- formed by distant weather systems
- never reach back of beach
12
Q
Destructive wave
A
- strong backwash & weak swash
- tall in relation to length
- common during winter storms
- remove material from coastline
- generally steep beach profile
- causes cliff face erosion
13
Q
Spring (high) and Neap (low) tides
A
- the spring tides are exceptionally high and the neap tides are very low as the gravitational pul (in spring tide) is pulling in the same direction
- in coastal management we need to know how high the spring tide is in order to build effective defences (e.g. a high enough sea wall)
14
Q
3 marine geomorphical processes
A
- erosion
- transportation
- deposition
15
Q
Processes of erosion
A
- hydraulic action (impact on rock of the sheer force of water)
- wave quarrying (breaking wave traps air as it hit cliff face)
- abrasion/corrosion (eroded material thrown against rock by waves)
- attrition (rocks slowly worn down into smaller and rounder particles
- solution (corrosion) (where seawater interacts with freshwater supplies, carbon based rock e.g. limestone may e dissolved)
16
Q
Factors affecting rate of erosion
A
- strength of waves
- weathering
- certain landforms reduce impact (beaches: increased distance a wave travels)
-headlands refract waves around them, reducing their erosive power - human activity
17
Q
Types of transportation
A
- traction (large particles pushed along seabed by force of water)
- suspension (small particles are carried along in water)
- saltation (pebble-sized particles are bounced along the seabed by force of water)
- solution (soluble materials dissolve in the water and are carried along)
18
Q
High energy coasts
A
- small particles (clay/sand) easily transported whilst larger and heavier material is deposited, forming shingle beaches
19
Q
Low energy coast
A
- even the smallest material is deposited forming mudflats and salt marshes
20
Q
Sub-aerial processes
A
- weathering
- mass movement
- runoff
21
Q
Coastal weathering types (3)
A
- biological
- chemical
- mechanical (physical)
22
Q
Biological weathering
A
- the breakdown of rocks by organic activity
- thin plant roots growing into small cracks in cliff face. These cracks widen as roots grow, which breaks up the rock
- water running through decaying vegetation becomes acidic, which leads to increased chemical weathering
23
Q
Chemical weathering
A
- involves a chemical reaction where salts may be dissolved or a clay like deposit may result which is then easily eroded
- ways in which it can happen:
> carbonation - rainwater absorbs carbon dioxide from the air to form a weak carbonic acid
> oxidation - iron -> musky red powder
> solution - dissolving
24
Q
Mechanical (physical) weathering
A
- involves the break up of rocks without any chemical reactions taking place
- freeze thaw weathering (water enters cracks -> freezes -> expands)
- salt crystallisation
- wetting and drying
25
Positive feedback
- if the rate of debris removal exceeds the rate of weathering and mass movement then a positive feedback can operate, as the rate of weathering and mass movement could increase
26
Negative feedback
- if debris removal is slow and ineffective, this will lead to a build up of an apron of debris (scree) that reduced the exposure of the cliff space. Weathering and mass movements rates will decrease
27
Types of mass movement
- soil creep/solifluction
- mudflow
- run off
- landslide/debris/slide/slump/slip
- rock fall
28
soil creep/solifluction
- the slowest but most continuous form of mass movement involving the movement of soil particles downhill. Particles rise and fall due to wetting and freezing and in a similar way to LSD, this causes soil to move down the slope
29
Mudflow
An increase in the water content of soil can reduce friction, leading to earth and mud to flow over underlying bedrock, or slippery materials such as clay. Water can get trapped within the rock increasing pore water pressures, which forces rock particles apart and therefore weakens the slope
30
Run off
- overland flow may erode the cliff ace and coastal area or pick up sediment , that then enters the littoral zone, when it is transported in he are via suspension.
31
Landslide/debris/slide/slump/slip
- contrary to a landslide, the slope is urged, so often occur in weak and unconsolidated clay and sand areas. Build up in pore water pressure leads to the land collapse under its own weight
32
Rock fall
- occurs on sloped cliffs (over 40 degrees) when exposed to mechanical weathering, though mostly occurs on vertical Cliff faces and can be triggered by earthquakes. It leads to scree (rock fragments) building up at the base of the slope. Scree is a temporal store which acts as an input to a coastal zone
33
Sediment cells
- stretch of coastline within which sediment movement is more or less contained
- generally boarded by 2 headlands or deep water and contain inputs, transfers and stores of sediments
- 11 in total however divided further into sub sediments
34
Transfers (flows)
- LSD (littoral) as well as onshore processes such as wind and currents
35
Sinks (stores)
- beaches, sand dunes, and offshore bars/banks/bands
36
Sources of sediment
- rivers (9% coastal sediment from rivers, flooding deposits)
- cliff erosion (mass movement adds huge amounts)
- offshore sediment (constructive waves)
- wind (blown from field/farmland, only small sediment and heavily dependant on wind direction)
37
Concordant coastlines
Rocks on these coastlines run parallel to he sea (present in south purbeck)
38
Discordant coastlines
Rocks on these coastlines run perpendicular to the sea (present in east purbeck)
39
Wave cut platform formation
- occurs at steep cliffs, hydraulic action and corrosion occurs around high tide line and creates a wave cut notch
- as notch continues to be eroded (and sub-aerial weathering awakens the cliff from the top) it becomes unstable and so cliff face falls off
- this leaves behind a wave cut platform
- over time process repeats
40
How a headland erodes to for a stack
- crack, cave, arch, stack, stump
- headland attacked by hydraulic action forming a cave, two caves form back to back forming an arch, weathering processes (lik freeze-thaw) attack roof of arch until it collapses leaving a stack
41
Depositional landforms
- beaches
- spit
- tombolo
Sand dune
- offshore bars
- barrier beaches/islands
42
Spit
- long narrow feature that extends from the mainland at the end of a drift aligned beach
- LSD moves sediment out determined by prevailing wind direction, change in direction of coastline leads sediment to continue upwards and outwards, this sediment projection can create a salt marsh due to sheltered, saline environment, the length of the spit will depend on any changing currents or rivers which will prevent sediments from being deposited.
43
Tombolo
- connects the mainland to an offshore island and is formed due to wave refraction off the coastal island reducing wave velocity, leading to deposition of sediments (they may be covered at high tide if they are low lying)
44
Barrier beach/Bars
- when a beach or spit extends across a bay to join two headlands. This traps water behind it leading it to the formation of a brackish lagoon which is separated from the sea.
45
Offshore bars
- region where sand is deposited
- as the waves don’t have enough energy to carry the sediment to shore. They can be formed when the wave breaks early, instantly depositing its sediment asa loose-sediment offshore bar
46
Swash aligned
- wave crests approach perpendicular to coast so there is limited LSD. Sediment doesn’t travel far along the Bach. Wave refraction may reduce the speed of high energy waves, leading to the formation of a shingle beach with larger sediment
47
drift aligned
- waves approach at a significant angle, so LSD causes the sediment to travel bar along the beach, which my lead to the formation of a spit at the end of the beach
- generally larger sediment is found at the start of the beach and weathered sediment moves further down beach through LSD (end of beach is more likely to contain smaller sediment)
48
Sand dunes (aeolian landform)
- accumulations of sand blown into mounds by the wind
49
Sand dune formation
- sand accumulates on the beach from LSD
- at low tide, the sand dries out allowing the prevailing winds to move the loose sand up beach
- large inter tidal zone for sand to be dry
- sand is transported by process of saltation
- debris on beach traps sand
- grass (lyne grass) growth which stabilises the dunes
50
Types of dunes in order
- Embryo dune (sand constantly moving, high wind speed, no more than 1m high)
- fore dune (drought resistant plants- lyne grass + marram grass , roots slowly bind together, more growth = more trapped sand)
- main ridge/yellow dune (greater diversity of plants, hummus layer builds up, dunes 5-10m high, 80% sand vegetated)
- fixed/grey dune (stable, 100% vegetation, 50-100m from sea, hummus darkens allow soil to form)
- dune slack (between mature dunes where water reaches the surface, plants adapted to damp- cotton grass, can get plenty soil)
- mature dune (found 100m from shore, undisturbed can support shrubs, trees, ash, birch, humans may plant fas growing trees)
51
Tidal range
- the difference in height between the high and low tide marks
52
Creep
- a method of transportation used by the wind for moving the largest material
53
Bedding plane
- the point where layers of sedimentary rock are joined. Provides a weakness for weathering and potential sliding surface for mass movement
54
Mudflats
Created by the deposition of fine slits and clays in sheltered low energy coastal environments such as estuaries
55
Salt marsh
An area of coastal grassland that is regularly flooded by sea water
56
Required conditions for mudflats and formation
- weather: storms can erode the marsh
- tidal regime: changes in tidal currents can increase erosion and alter species (need low energy)
- wave type: changes in direction, nature and size can affect marsh stability
- climate: affects species types, growth rates and sea levels
- sea level: rise can upset equilibrium and destroy the marshes
- human action: commercial, industrial, and recreational activity can damage marsh (need lack of intervention
57
Pioneer species
First plant to colonise an area e.g eelgrass
58
Flocculation
Fine particles bind together and are then deposited
59
Halophytes
Salt tolerant plants
60
Succession on saltmarshes
- tidal currents slow and so begin to deposit material
- fine grains of material goes through flocculation. These eventually form uneven mudflats
- these mudflats have pioneer plant species (eel grass) which are halophytes and tolerate periodic soaking -> gradually cause vegetation all over the mudflat and more plants colonise mudflat.
- vegetation slows tidal currents causing sediment to be deposited
- these processes raise mudflats from between 2mm and 30mm per year and provides food for small invertebrates
61
Eustatic change
A global change in sea level resulting from a fall or rise in the level of the sea itself
>thermal expansion: where volume of water increases as it gets warmer
>land ice melting: melting of glaciers and ice sheets
62
Isostatic change
- local changes in sea level resulting from the land rising and falling due
63
emergent landscape occurs due to
Isostatic rebound (land going higher) or eustatic fall (sea level falls) -> most commonly Isostatic rebound
64
submergent landscape occurs due to
Due to Isostatic fall or eustatic rise
65
Emergent coastal landforms
- where the land has been raised in relation to the coastline such as:
>arches, stacks, stumps
>raised beaches (relic cliffs)
66
Submergent coastlines
- occur when the sea level rises or the coastline sinks in relation to the sea such as:
> rias
> fjords
> Dalmatian coasts
67
Rias
- formed when rising sea levels flood narrow winding inlets and river valleys
- they are deeper at the mouth of the inlet, with the water depth decreasing further inland
68
Fjords
- fjords are formed when rising sea levels flood deep glacial valleys to create natural inlets and harbours
- they are deeper in the middle section than they are at the mouth, with the hallowed section identifying where the glacier left the valley
69
Dalmatian coasts
- this type of coastline occurs when the valleys running parallel to the coast become flooded as a results of sea level Chang. This leaves a series of narrow, long and rugged islands
70
Why is it important we manage the coast
- 1/5 uk population live within the coastal zone
- 58% farming land
- 30% covered. By buildings, roads and recreation facilities
71
The coastline needs managing for 3 different reasons
- coastal erosion
- coastal flooding
- failure of former defences
72
Possible management strategies
- hold the line (maintain/build new defences to ensure coastline stay where it is)
- advance the line (build new defences seaward of existing line)
-retreat the line (managed retreat) (allow coastline to retreat due to flooding&erosion but closely manage the rate and location of this retreat)
- DO nothing (low value areas left to natural coastal processes)
73
Factors needing considering
- who is impacted
- is there ecological importance
- what is the value of the area economically
- likelihood of success
- what are the alternatives
- cost of defence
74
Shoreline management plans (SMP’s) [aims]
- promote long term management policies into 22nd century
- access the risk associated with coastal evolution
- address risks in a sustainable way
- ensure management plans comply with nature conservation
- provide policy for coastal management
- assess risks to developed,natural and historic environments
- ‘live’ documents which are constantly reviewed
- promote long term management policies 22nd century
75
Integrated coastal zone management (ICZM’s)
- large section of coastline are managed with one integrated strategy
- recognises that coastal management must be sustainable whereby economic development is important, but not prioritised over protection of the coastal environment
76
Soft engineering strategies
- beach nourishment
- dune regeneration
- managed retreat
- land-use management
77
Beach nourishment
- the addition of sand or pebbles to an existing beach to make it higher/wider -> sediment usually dredged from the nearby seabed; costing $300,000 per 100m
- ADVANTAGES: relatively cheap and easy to maintain, looks natural+blends in with existing beach, increases tourist potential due to bugger beach
- DISADVANTAGES: needs constant maintenance because of the natural processes of erosion and longshore drift
78
Dune regeneration
- marram grass can be planted to stabilise dunes, areas can be fenced in to keep people off newly planted dunes; costing $200 to $2000 per 100m
- ADVANTAGES: maintains a natural coastal environment, provides important wildlife habitats, relatively cheap and sustainable
- DISADVANTAGES: time consuming to plant marram grass, people may respond negatively to being kept off certain ones
79
Managed retreat
- the controlled flooding of a low lying coastal area and the creation of a wetland area such asa salt marsh; costing between $5000-10,000
- ADVANTAGES: cheap compared to hard, creates salt marshes which can provide habitats for wildlife + a natural defence against erosion and flooding
- DISADVANTAGES: requires long-term planning, requires large initial investment
80
Land-use management
- allow the planning and management of land types to determine which areas of land should be chosen for which uses of land; costing nothing
- ADVANTAGES: environmental protection, avoidance of urban sprawl
- DISADVANTAGES: high costs initially, long term planning
81
Hard engineering strategies
- sea walls
- groynes
- gabions
- revetments
- barrages
- offshore reefs
82
Sea walls
- stone or concrete walls at foot of a cliff, or at the top of a beach. They usually have a curved face to reflect wavering back into the sea; costing $6000 per metre
- ADVANTAGES: effective prevention, often have a promenade for people to walk along
- DISADVANTAGES: they reflect wave energy rather than absorbing it, they can be intrusive and unnatural looking, very expensive to build and maintain
83
Groynes
- timber or rock structures built at right angles to the coast, they trap sediment being moved along the coast by LSD building up the beach; costing between $5000-10,000each (at 200m intervals)
- ADVANTAGES: work with natural processes to build up the beach which increases tourist potential and protects the land behind it, not too expensive
- DISADVANTAGES: starve beaches further along the coast of fresh sediment (as they interrupt LSD)(e.g.Bournemouth -> Barton on sea) often leading to increased erosion elsewhere, unnatural and can be unattractive
84
Gabions
- rectangular baskets fabricated from a hexagonal mesh of heavily galvanised steel wire; costing $10-15 per square foot
- ADVANTAGES: absorb the energy of waves, allows the build up of a beach, fairly cheap
- DISADVANTAGES: they can be expensive to obtain and transport the boulders, can also look unattractive
85
Revetments
- sloping wooden, concrete or rock structures places at the foot of a cliff or the top of a beach, they break up the waves energy; costing up to %4500 per metre
- ADVANTAGES: they are relatively inexpensive to build
- DISADVANTAGES: intrusive and very unnatural looking they can need high levels of maintenance
86
Barrages
- a type of low-head, diversion dam which consists of a number of large gates that can be opened or closed to control (the amount of water passing through); Severn costing $500 million
- ADVANTAGES: no pollution, renewable, no fuel costs, minimal running costs
- DISADVANTAGES: prevents free access by boat, spoils the view, alters habitat affecting wildlife, initially expensive
87
Offshore reefs
- a partly submerged rock barrier designated to break up waves before they reach the coast; similar cost to rock armour -> dependant on materials
-ADVANTAGES: an effective permeable barrier
- DISADVANTAGES: visually unappealing and a potential navigation hazard
Physical Geography (coasts)
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