Coastal landscapes and change Flashcards
What is the littoral zone?
The littoral zone is the area of shoreline where land is subject to wave action. It’s subdivided into offshore, nearshore, foreshore and backshore and (ONFB - OKAY NOW FRY BANANAS!) it is constantly changing.
sea - offshore - nearshore - foreshore - backshore - field with lots of cows
What is the backshore?
The area above the high tide mark, affected by wave action only during major storm events.
What is the foreshore?
The area between the high tide and the low tide mark.
What is the nearshore?
The area of shallow water beyond the low tide mark, within which friction between the seabed and waves distorts the wave sufficiently to cause it to break. (breaker zone) There may be a breakpoint bar between the offshore and nearshore zones.
What is the offshore?
The area of deeper water beyond the point at which waves begin to break. Friction between the waves and the sea bed may cause some distortion of the wave shape.
Why is the littoral zone dynamic?
There are constantly changing inputs, through flows, and outputs of energy and material. (short term)
There are also long-term changes, e.g. sea level variation due to climate change.
And short term changes (e.g. high and low tide variation over the lunar month; wave energy variation due to weather conditions)
Three types of coastal landscape
- Rocky, cliffed coastline - high relief, resistant rocks, high energy environment, erosion > deposition, destructive waves
- Sandy coastline - low relief with sand dunes and beaches, less resistant rocks, low energy environment, deposition > erosion, constructive waves
- Estuarine coastline - low relief with salt marshes and mudflats, form in river mouths where deposition > erosion, low energy environment, less resistant rock
How can coasts be classified?
Longer-term criteria
- Geology
- Changes of sea level
Shorter-term processes
- Inputs from river, waves and tides
Expand the term ‘geology’
All the characteristics of land, including rock type and structure.
It can be used to classify coasts are rocky, sandy or estuarine.
As well as concordant and discordant.
How can sea level change be used to classify coasts?
Sea level change be used to classify coasts as emergent or submergent.
This can be caused by:
- Tectonic processes can lift sections of land up, causing local sea fall, or lead sections of land to subside, causing local sea rise.
- Climate change
Eustatic and Isostatic change
Eustatic change - When the sea level itself rises or falls
Isostatic change - When the land rises or falls, relative to the sea
Concordant coastlines
Concordant coastlines are where the rock strata run parallel to the coast. The rock type varies between different concordant coasts and normally consist of bands of more resistant and less resistant rock.
Discordant coastlines
The geology alternates between bands of more-resistant and less-resistant rock and the rock strata run perpendicular to the sea, which can create successions of headlands and bays; less resistant rocks are eroded faster than the more resistant rocks, which
leads to the formation of bays.
What are dalmation coasts?
Dalmation coasts are another type of concordant coastline. They have formed as a result of a rise in sea level. Valleys and ridges run parallel to each other. When the valleys flooded because of a rise in sea level, the tops of the ridges remained above the surface of the sea - as a series of offshore islands that run parallel to the coast.
What are Haff coasts?
Haff coasts also consist of concordant features - long spits of sand and lagoons - aligned parallel to the coast.
How to remember littoral zone formation?
OKAY NOW FRY BANANAS
Offshore, Nearshore, Foreshore, Backshore
3 coastal depositional processes
- Longshore drift redistributes material along a beach
- Constructive waves drop beach material because they have less energy and have stronger swash than backwash
- Obstacles on beach (such as groynes) / marram grass create a low-energy zone where material is deposited
Dune Successional Development
- Embryo dunes form when seaweed driftwood or litter provides a barrier or shelter to trap sand.
- As the embryo dune grows, it is colonised by pioneer plants, like sea couch grass and sea rocket.
- Pioneer plants stabilise the sand allowing marram grass to colonise.
- As the marram grass dies, it adds humus to the sand, creating soil. A grey dune develops, with plants such as gorse.
What do pioneer plants do?
Pioneer plants stabilise the sand allowing marram grass to colonise.
3 parts of sediment cell model
- Sources
- Transfers
- Sinks
Methods of sediment transportation
Traction
Saltation
Suspension
Solution
Traction
Where large, heavy load items are rolled along the sea bed,
e.g. boulders, cobbles and pebbles
Saltation
Where lighter sediment bounces along
Sand particles are usually transported this way
Suspension
Where very light sediment is carried aloft within a body of water or air
E.g. silt or clay particles
Suspended clay particles, give the sea a cloudy, muddy brown colour on soft-rock coasts, e.g. Holderness
Solution
Where sediment is carried dissolved within the water
Mass movement - flows
Soil creep
Solifluction
Earth flows and mudflows
Mass movement - slides
Rock falls
Rock/debris slides
Slumps
Soil creep
It is a very slow downhill movement of individual soil particles
Solifluction
When the top layer of soil thaws in the summer - but the layer below remains frozen - the surface layer becomes saturated and flows over the frozen subsoil and rock.
Earth flows and mudflows
An increase in the amount of water can reduce friction - causing earth and mud to flow over underlying bedrock.
Rock falls
- Most likely to occur when rock/cliff faces are exposed to mechanical weathering
- Occur on slopes over 40*
- The material, once broken away from the source, either bounces vertically to form scree at the foot of the slope/cliff.
Rock/debris slides
- Rocks that are jointed, or have bedding planes roughly parallel to the slope or cliff surface, are susceptible to landslides.
- An increase in the amount of water can reduce friction - causing sliding
Slumps
- Often occur in saturated conditions and on moderate to steep slopes
- There is a rotational movement in slumping
- They are common where softer materials overlie more-resistant or impermeable rock, such as limestone or granite
- Slumping causes rotational scars
- Repeated slumping creates a terraced cliff profile
How do salt marshes develop?
They develop in sheltered areas where deposition occurs, where salt and fresh water meet, where there are no strong tides or currents to prevent sediment deposition and accumulation.
two types of beaches
swash-aligned - sediment moves up and down the beach with little lateral transfer
drift-aligned - sediment is transferred along the coast by longshore drift
How are offshore bars formed? What are they?
Destructive waves erode sand from the beach with their strong backwash and deposit it offshore in bars. They are submerged (or party exposed) ridges of sand or coarse sediment.
What is a bar?
Where a beach or spit extends across a bay to join two headlands. They can also trap water behind them to form lagoons
What is a tombolo?
A tombolo is a beach that has formed between a small island and the mainland. Deposition occurs where waves lose their energy and the tombolo begins to build up. They may be covered at high tide.
What is a cuspate foreland?
A triangular-shaped headland that extends out from the main coastline. It occurs where a coast is exposed to longshore drift from opposite directions. Sediment is deposited at the point where the two meet, which forms a natural triangular shape as it builds up. As vegetation begins to grow on the deposited sediment, it helps to stabilise the landform and protect it from storms that could erode it.
types of weathering
mechanical, chemical, biological
Types of mechanical weathering
Freeze-thaw weathering
Salt-weathering
Wetting and drying
Hard engineering structures
Groynes Sea walls Rock armour Revetments Offshore breakwater
groynes
Timber or rock structures built at right angles to the coast. They trap sediment being moved along the coast by longshore drift - building up the beach.
sea walls
Made of stone or concrete at the foot of a cliff, or at the top of a beach. They usually have a curved face to reflect waves back into the sea.
Rock armour
Large rocks placed at the foot of a cliff, or at the top of a beach. It forms a permeable barrier to the sea - breaking up the waves, but allowing some water to pass through.
revetments
Sloping wooden, concrete or rock structures - placed at the foot of a cliff or the top of the beach. They break up the waves’ energy.
offshore breakwater
A partly submerged rock barrier, designed to break up the waves before they reach the coast.
advantages of groynes
- The built-up beach increases tourist potential and protects the land behind it
- Groynes work with natural processes to build up the beach
- Not too expensive
advantages of sea walls
- Effective prevention of erosion
- They often have a promenade for people to walk along
advantages of rock armour
- It is relatively cheap and easy to construct and maintain
- Absorbs wave energy without causing reflection
advantages of revetments
- They are relatively inexpensive to build
advantages of offshore breakwater
- An effective permeable barrier
disadvantages of groynes
- They starve the beach further along the coast of fresh sediment, because they interrupt longshore drift. This often leads to increased erosion elsewhere.
- Groynes are unnatural and rock groynes can be very unattractive
disadvantages of sea walls
- They reflect wave energy, rather than absorbing it
- They can be intrusive and unnatural looking
- They are very expensive to build and maintain
disadvantages of rock armour
- The rocks are usually from somewhere else (e.g. granite), so they don’t fit in with the local geology and can look out of place.
- It can be very intrusive
- The rocks can be dangerous for people clambering over them
disadvantages of revetments
- They are intrusive and very unnatural looking
- They can need high levels of maintenance
disadvantages of offshore breakwater
- It is visually unappealing
- It’s a potential navigation hazard
cost of groynes
£5000 to £10 000 each (at 200-metre intervals)
cost of sea walls
£6000 a metre
cost of rock armour
£100 000 to £300 000 for 100 metres
cost of revetments
up to £4500 a metre
cost of offshore breakwater
Similar to rock armour - depending on the materials used.
Soft engineering structures
- Beach nourishment
- Cliff regrading and drainage
- Dune stabilisation
- Marsh creation
beach nourishment
The artificial addition of sediment to an existing beach to:
- replace sediment lost by erosion,
- to enlarge the beach
- so that it dissipates wave energy and reduces erosion and
- increases the amenity value of the beach.
Cliff regrading and drainage
Cliff regrading reduces the angle of the cliff, to help stabilise it.
Drainage removes water to prevent landslides and slumping.
Dune stabilisation
Marram grass can be planted to stabilise dunes. Areas can be fenced in to keep people off newly planted dunes.
Marsh creation
A form of managed retreat, by allowing low-lying coastal areas to be flooded by the sea. The land then becomes a salt marsh.
advantages of beach nourishment
- Relatively cheap and easy to maintain
- It looks natural and blends in with the existing beach
- It increases tourist potential by creating a bigger beach
advantages of cliff regrading and drainage
- Regrading can work on clay or loose rock, where other methods won’t work.
- Drainage is cost-effective
advantages of dune stabilisation
- It maintains a natural coastal environment
- It provides important wildlife habitats
- It is relatively cheap and sustainable
advantages of marsh creation
- It is relatively cheap, but it often involves land reverting to its original state before it was managed for agriculture.
- It creates a natural defence - providing a buffer to powerful waves
- It creates an important wildlife habitat
disadvantages of beach nourishment
- It needs constant maintenance, because of the natural processes of erosion and longshore drift
disadvantages of cliff regrading and drainage
- Regrading effectively causes the cliff to retreat
- Drained cliffs can dry out and lead to collapse (rock falls)
disadvantages of dune stabilisation
- It is time consuming to plant marram grass
- People may respond negatively to being kept off certain areas
disadvantages of marsh creation
- Agricultural land is lost
- Farmers or landowners need to be compensated
cost of beach nourishment
£300 000 for 100 metres
cost of dune stabilisation
£200 to £2000 for 100 metres
cost of marsh creation
cost is variable - depending on the size of the area left to the sea
