Coastal Systems and Landscapes Flashcards
Components of a system
1) Inputs
2) Outputs
3) Flow/Transfers
4) Stores/Components.
Negative Feedback
When a change in the system causes other changes that have the opposite effect.
Positive Feedback
When a change in the system causes other changes that have a similar effect.
Wind
Created by air moving from areas of high pressure to areas of low pressure.
What changes the effect of a wave?
The wave height - it is affected by the wind speed and the fetch of the wave.
Waves
Created by the wind blowing over the surface of the sea. The friction between the wind and the surface of the sea gives the water a circular motion.
The fetch of a wave
The maximum distance of sea the wind has blown over in creating the waves.
Constructive Waves
Low frequency (6-8 per minute)
They’re low and long, which gives them a more elliptical cross profile.
The powerful swash carries material up the beach and deposits it.
Destructive Waves
High and steep with a more circular cross profile.
They have a higher frequency (10-14 waves per minute).
The strong backwash removes material from the beach.
Tides
The periodic rise and fall of the ocean surface, caused by the gravitational pull of the moon and the sun.
Currents
The general flow of water in one direction - it can be caused by wind or by variations in water temperature and salinity.
High energy Coasts
receive high inputs of energy in the form of large, powerful waves.
These can be caused by strong winds, long fetches and steeply shelving offshore zones.
The rate of erosion is often higher than the rate of deposition.
Low energy coasts
receive low inputs of energy in the form of small, gentle waves.
These can be caused by gentle winds, short fetches and gently sloping offshore zones.
The rate of deposition is often higher than the rate of erosion.
Sediment Budget
The difference between the amount of sediment that enters the system and the amount that leaves
Sediment/ Littoral Cells
Lengths of the coastline that are pretty much self-contained for the movement of sediment.
Corrasion (abrasion)
Bits of rock and sediment transported by the waves smash and grind against rocks and cliffs, breaking bits off and smoothing surfaces.
Hydraulic Action
air in cracks in cliffs is compressed when waves crash in. The pressure exerted by the compressed air breaks off rock pieces.
Cavitation
As waves recede, the compressed air expands violently, again exerting pressure on the rock and causing pieces to break off.
Wave Quarrying
The energy of a wave as it breaks against a cliff is enough to detach bits of rock.
Solution (corrosion)
Soluble rocks get gradually dissolved by the seawater
Attrition
Bits of rock in the water smash against each other and break into smaller bits.
Suspension
Very fine material, such as silt and clay particles, is whipped up by turbulence and carried along in the water. Most eroded material is transported this way.
Saltation
larger particles, such as pebbles or gravel, are too heavy to be carried in suspension. Instead, the force of water causes them to bounce along the sea bed.
Traction
Very large particles, e.g. boulders, are pushed along the sea bed by the force of the water.
Sub-aerial weathering
The gradual breakdown of rock by agents such as ice, salt, plant roots and acids.
Salt weathering
Caused by saline water which enters pores or cracks in rocks at high tide.
Freeze-Thaw weathering
occurs in areas where temperatures fluctuate above and below freezing.
Water enters the joints and crevices in rocks. The water freezes and expands, over time the repeated freeze-thaw action weakens the rocks and causes pieces to fall off.
Wetting and Drying
Some rocks contain clay. When clay gets wet, it expands and the pressure caused by this breaks fragments off the rock.
Chemical Weathering
The breakdown of rock by changing composition.
Eustatic Change
caused by a change in the volume of water in the sea, or by a change in the shape of the ocean basins.
Isostatic Change
Caused by vertical movements of the land relative to the sea. Any downward movement of the land causes sea level to rise locally, while uplift of land causes sea level to fall.
Rias
formed where river valleys are partially submerged. They have a gentle long- and cross-profile. They’re wide and deep at their mouth, becoming narrower and shallower the further inland they reach.
Fjords
drowned glacial valleys. They’re relatively straight and narrow, with very steep sides. They have a shallow mouth caused by a raised bit of ground formed by deposition of material by the glacier. They’re very deep further inland.
Dalmatian Coasts
Formed in areas where valleys lie parallel to the coast, an increases in sea level. Valleys are flooded, leaving islands parallel to the coastline.
The four options for coastal management
Hold the line, advance the line, no active involvement, managed realignment
Sea wall
The wall reflects waves back out to sea, preventing erosion of the coasts. It also acts as a barrier to prevent flooding.
Cost and disadvantages of sea walls
Expensive to build and maintain
It creates a string backwash which erodes under the wall.
Revetment
slanted structures built at the foot of cliffs. They can be made from concrete, wood or rocks. Waves break against them, which absorb wave energy and so prevent cliff erosion
Costs and disadvantages of revetments
Expensive to build, but relatively cheap to maintain.
They create a strong backwash which erodes under the revetments.
Gabions
Rock-filled cages, usually built at the foot of cliffs. They absorb wave energy and so reduce erosion
Cost and disadvantages of gabions
cheap cost but ugly
Riprap
Boulders piled up along the coast. They absorb wave energy and so reduce erosion.
Cost and disadvantages of riprap
fair cheap cost but can shift in storms
Groynes
fences built at right angles to the coast. They trap beach material transported by longshore drift. This creates wider beaches, which slow the waves and so gives greater protection from flooding and erosion.
Cost and disadvantages of groynes
Quite cheap
They starve down-droft beaches of sand. Thinner beaches don’t protect the coast as well, leading to greater erosion and flooding.
Breakwaters
Concrete blocks or boulders deposited off the coast. They force waves to break offshore. The waves’ energy and erosive power are reduced before they reach the shore.
Cost and disadvantages of breakwaters
Expensive
Can be damaged in storms
Earth Banks
Mounds of earth act as a barrier to prevent flooding
cost and disadvantages of earth bank
Quite expensive
can be eroded
Tidal Barrier
built across river estuaries. They contain retractable floodgates that can be raised to prevent flooding from storm surges.
Cost and disadvantages of Tidal Barriers
VERY expensive
Tidal Barrage
Dams built across river estuaries. Their main purpose is to generate electricity. Water is trapped behind the dam at high tide. Controlled release of water through turbines in the dam at low tide generates electricity. They also prevent flooding from storm surges.
Cost and disadvantages of Tidal barrage
Very expensive
They disrupt sediment flow, which may cause increased erosion elsewhere in the estuary
Beach nourishment
Sand and shingle are added to beaches from elsewhere. This creates wider beaches, which reduce erosion of cliffs more than thin beaches
Beach stabilisation
Reducing the slope angle and planting vegetation, or by sticking stakes and old tree trunks in the beach to stabilize the sand. It also creates wider beaches, which reduce erosion of cliffs.
Dune regeneration
Where sand dunes are created or restored by either nourishment or stabilisation of the sand. They also provide a barrier between land and sea, absorbing wave energy and preventing flooding and erosion
Why is land use management important for dune regeneration
The vegetation needed to stabilize the dune can easily be trampled and destroyed, leaving the dune vulnerable to erosion.
Creating marshlands from mudflats
The vegetation stabilises the sediment, and the stems and leaves help reduce the speed of the waves. This reduces their erosive power and how far the waves reach inland, leading to less flooding of the area around the marsh.
Coastal Realignment
involves breaching an existing defence and allowing the sea to flood the land behind. Over time, vegetation will colonies the land and it’ll become marshland.
Shoreline Management Plans
The coastline is split into stretches bu sediment Cells. For each cell, a plan is devised for how to manage different areas with the aim of protecting important sites without causing problems elsewhere in the cell.
Integrated Coastal Zone Management
considers all elements of the coastal system when coming up with a management strategy. It aims to protect the coastal zone in a relatively natural state, whilst allowing people to use it and develop it in different ways.
