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Coastal Systems and Landscapes - Coggle Diagram
Coastal Systems and Landscapes
Systems and Processes
Components
Characteristic erosional and depositional coastal landforms
Outputs
Accumulation of sediment above the tidal limit
Sediment removed beyond local sediment cells
Dissipation of wave energy
Inputs
Sediment
Geology of the coastline
Energy from waves, tides, and sea currents
Sea level change
Sources of Energy in Coastal Environments
Waves
Constructive Waves
Low frequency of around 6-8/min
Stronger swash than backwash
Low height with long wavelength, often up to 100m
Material is slowly but constantly moved up the beach, leading to the formation of ridges
Destructive Waves
High frequency of 10-14/min
Stronger backwash than swash
High wave height with a steep form
Material is pulled down the beach, leading to steeper beach profiles
Wave Refraction
Energy of the waves is concentrated on the headland, causing greater erosion
Low-energy waves spill into the bay, resulting in beach deposition
When waves approach a coastline that is not uniform in shape, the waves become refracted and increasingly parallel to the coastline
Wind
Prevailing wind direction controls the direction that waves approach the coastline, and direction of the transport of sediment
Fetch - the distance of open water which a wind blows uninterruptedly. Fetch helps to determine the magnitude and energy of waves
Where wind speeds are persistently high and uninterrupted, wave energy is likely to be higher
Wind can pick up and remove sediment from the coast and use it to erode other features
Coastal Processes
Transportation
Saltation
Small stones bounce along the seabed and beach, associated with relatively high energy conditions
Suspension
Very small particles of sand and silt are carried along by moving water. Large amounts of suspended material can cause a milky or murky appearance of the water
Traction
Large stones and boulders are rolled and slid along the seabed and beach, this happens in high energy environments
Longshore Drift
When waves approach the shore at an angle and material is pushed up the beach at the same angle as the waves
Backwash drags material down perpendicularly back down the beach
This causes sediment to move in a zigzag fashion across the beach
Marine
Wave Quarrying (Cavitation)
A breaking wave traps air as it hits a cliff face
As the water pulls back, there is an explosive effect of the air under pressure being released. This will weaken the cliff face over time
Abrasion / Corrasion
The impact on the rocks from sediment and debris picked up by waves
Hydraulic Action
The impact on rocks from the force of the water itself (no debris)
Attrition
The rocks in the sea which carry out abrasion are slowly worn down into smaller and rounder pieces
Solution (Corrosion)
The dissolving of calcium based rocks (limestone) due to acidic water
pH of seawater is between 7.5-8.5, however rainwater is slightly acidic so conditions for solution may occur
Evaporation of salts from water in the rocks produces crystals, which expand as they form, weakening the rocks
Sub-aerial weathering
Biological Weathering
Processes that lead to the breakdown of rocks by the action of vegetation and coastal organisms
Algae attaches itself to rocks which can prise away loose rocks from the seafloor. Some algae can also secrete chemicals capable of promoting solution. Some animals can weaken cliffs by as they burrow or dig into them
Chemical Weathering
Hydration:
the addition of water to minerals in the rock causes the rock to expand, which can cause the rock to disintegrate
Hydrolysis:
where mildly acidic water reacts with minerals within rocks to create clays and dissolvable salts. This weakens the rock
Oxidation
: causes rocks to disintegrate when the oxygen dissolved in water reacts with some rock minerals. Especially affects iron-rich rocks and is visible brownish or yellowish stain on rocks
Carbonation:
when carbon dioxide dissolved in rainwater makes a weak carbonic acid. This will dissolve calcium-rich rocks
Mechanical/Physical weathering
Freeze-thaw:
water enters cracks in rocks and freezes when temperatures fall below 0°C
The water will expand as it freezes, which will create cracks in the rocks. As the process continues, the cracks will widen and pieces will eventually break off
Mass Movement
Rock Falls:
occur from cliffs undercut by the sea, or on slopes affected by mechanical weathering
Mudflows:
Heavy rain can cause large quantities of fine material to flow downhill, when the soil is saturated can water can't percolate deeper into the ground
Landslides:
when cliffs made of softer rocks slip, usually as a result of heavy rainfall
Rotational Slip/Slumping:
Where softer material overlies much more resistant materials. Excessive lubrication can cause whole sections of cliff to move downwards with a concave slide plane, producing a rotational movement
Soil Creep:
occurs where there is a very slow, almost imperceptible, but continuous movement of soil particles downslope.
Coastal Landscape Development
Landforms of Coastal Erosion
Cliffs and Wave-Cut Platforms
Further erosion will cause the cliff to collapse and the cliff line will begin to retreat
After successive collapses, a gently sloping wave-cut platform is formed at the base of the cliff
Erosion is concentrated at the base of a cliff, causing the base to become undercut, forming a
wave-cut notch
The platform continues to grow, meaning that waves have to travel further to reach the cliff line, reducing the rate of erosion. Therefore wave-cut platforms usually only reach up to
500m
in length
Cliff Profile Features
Cave:
formed when a cliff is undercut, usually from a combination of marine processes
Blowhole:
when a cave is extended to the top of the cliff, if erosion continues vertically upwards
Geo:
narrow, steep-sided inlet formed when the sea cuts inland along a joint
Arch:
when a cave extends to the other side of the headland, meeting another cave, due to refraction around the headland
Stack:
as a cliff recedes, the arch will eventually collapse due to gravity, erosion, and weathering. This leaves an isolated portion of rock (stack)
Stump:
the sea will exploit the wave-cut notch at the base of a stack, leading to it's collapse. A small portion of rock may be left behind (stump)
Headlands and Bays
Wave refraction then causes the headlands to receive the highest-energy waves and become more vulnerable to erosion than bays
Bays receive low-energy waves that allow sediment to accumulate and form beaches
Softer rock is eroded more quickly, forming bays. Leaving the more resistant rock as headlands
Landforms of Coastal Deposition
Spits
Formation:
formed when longshore drift moves sediment along the coastline, and a spit is formed where the material is deposited. Over time the spit will grow and develop a hooked end if wind direction changes further out.
Simple Spits
Do not have minor spits or recurved ridges, along their landward edge
Either straight or recurved
Compound Spits
May have similar features to simple spits
Have a number of recurved ridges or minor spits, along their landward edge, possibly marking the position where they terminated in the past
Salt Marshes
Low-energy waves enter this area and deposit finer material, e.g. silt and clay,
These deposits build up and are colonised by vegetation to become salt marshes
Sheltered area between the land and the spit
Beaches
Accumulation of sediment found at the point where land meets the sea. Mainly made up of sand and shingle.
Barrier Beaches
Elongated bank of deposited sand or shingle lying parallel to the coastline and not submerged by incoming tides
Where the bank is high enough to allow sand dunes to develop, it is known as a
barrier island
Often the sheltered area between the barrier beach and the land becomes a lagoon or coastal marsh, or mangrove swamps in more tropical areas
Sea Level Change
Stage 2:
the weight of the ice causes the land surface to sink. This causes
isostatic
sea level rise
Stage 3:
the climate begins to get warmer, and the ice starts to melt. This causes
eustatic
sea level rise
Stage 1:
as the climate gets colder, there is an increase in snowfall, which eventually turns into glacier ice. This water is not cycled back to the sea, causing
eustatic
sea level fall
Stage 4:
as the ice melts, the land moves back up to it's previous position, leading to
isostatic
sea level fall
Impacts of Climate Change on Coasts
Seawater can contaminate groundwater
Loss of homes, roads, agricultural land, power stations, etc., due to flooding
Increased coastal flooding and erosion
Coastal Management
Soft Engineering
Managed retreat
Land-use management
Dune regeneration
Do nothing
Beach nourishment
Shoreline Management Plans (SMPs)
They aim to plan for the short (0-20 years). medium (20-50 years), and long term (50-100 years)
Designed to identify the most sustainable approach to managing the flood and coastal erosion risks to the coastline
Address the risks in a sustainable way
Ensure management plans comply with national and international nature conservation
Assess the risks associated with the evolution of the coast
Provide a foundation for future research and the development of new coastal management strategies
22 SMPs around the coast of England and Wales
Hard Engineering
Rock Armour
Gabions
Sea Walls
Revetments
Groynes
Offshore Reefs
Barrages
Cliff Fixing
Integrated Coastal Zone Management (ICZM)
Covers information collection, planning, decision-making, management, and monitoring of implementation
Employs an
'ecosystem-based approach'
that operates within the limits of natural resources and ecosystems
Aims for the coordinated application of the different policies affecting the coastal zones
Agriculture
Tourism
Fishing
Nature conservation
Infrastructure development
Offshore wind energy
Case Study:
Pevensey Bay, East Sussex
Coastal Processes
Beaches become flatter during major storms, reducing wave energy and preventing waves from reaching the top of the shingle bank, thus reducing the flood risk
Movement of sediment is becoming increasingly irregular
Prevailing winds from the southwest move material towards the northeast, creating beaches that are more parallel to the waves
Flooding is a bigger risk than erosion here
Beach Maintenance Strategies
Recycling
Dump trucks and bulldozers redistribute sand and shingle from areas of net gain to areas of net loss
This is required after especially stormy weather
Some areas have a net gain of sediment, some have a net loss, and others do not change
Bypassing
Either added directly to the beach or is stockpiled as an emergency source
Trucks transfer 5,000-15,000m³ of surplus shingle to the west
(during winter)
Recharge
Lorries transport 5,000m³ around the harbour each year
Remaining 20,000m³ is dredged from the sea floor just off shore
25,000 m³ of sediment is annually lost due to LSD
Rather than using bulldozers, 20,000m³ is left in situ and LSD naturally redistributes the sediment
(saving time and money)
Reprofiling
Destructive waves in winter storms move sediment further down the beach
Bulldozers are used to push the material back up the beach
Groynes
Instead, each groyne is removed when it fails
The wood is reused to either repair the remaining groynes or made available to local residents to be recycled and reused
Restoring the 150 groynes would be too expensive
Beach Surveys
Twice a month, a quad bike with a GPS receiver surveys the beach
The data is used to produce 3D models of the beach and shingle bank
This maintains the sustainability of the project as replenishment, reprofiling, and recycling can be targeted only where needed
Geographical Context
Sandstone to the east, and chalk to the west
Longshore drift action from west to east
Low-lying area of softer sediments
Sea level rise and longshore drift have created a natural shingle barrier which extends for
9km