Coastal environments Flashcards
Fetch
Length of time and distance over open water that the wind has blown to create a wave
Features of constructive waves
- Long wavelength
- Shallow gradient waves
- Strong swash
- Weak backwash
- Deposition of material
Features of destructive waves
- Steep gradient waves
- Tall waves with short wavelength
- Weak swash
- Strong backwash
- Erosion of material
Hydraulic action
Waves hit cliffs and force air into cracks
Abrasion
Waves pick up pebbles and hurl them against the cliff
Solution
The dissolving of soft rocks by the sea
Attrition
Pebbles carried by waves collide with each other and become smaller and more rounded over time
Deposition
Occurs when waves lose energy/material carried is too large to transport with the amount of energy the wave has
Longshore drift
- Wave swash approaches beach at an angle (the same direction as the prevailing wind)
- Backwash is at a 90-degree angle due to gravity
- Process repeats, moving sediment along the beach
- Smaller material is transported further as it requires less energy
Solution
When minerals in rocks like chalk and limestone are dissolved in seawater and carried within. The load is not visible
Suspension
Small particles such as silts and clay are in the flow of the water
Saltation
Where small pieces of shingles or large sand grains are bounced along the sea bed
Traction
Where pebbles and larger material are rolled along the sea bed
Weathering
The breaking down of rocks and other materials in situ
Mechanical weathering
Processes such as freeze-thaw, salt crystal growth, and wetting and drying of clay rich rocks
Biological weathering
When rocks are broken down by things such as plant roots, burrowing animals and nesting birds
Chemical weathering
Processes such as carbonation, oxidation and acid rain
Slumping
Waves erode the cliff base and cause instability. Rainwater permeates through the rock, saturating it, until it becomes unstable and slumps along bedding planes. Leads to a stepped appearance to the cliff
Sliding
Weathering loosens rock, which slides down off bedding planes. Leads to landslides and mudslides
Geology
Rock type e.g. granite or chalk
Lithology
Characteristics of the rock e.g. relative hardness and permeability
Discordant geology
Rock outcrops are at 90 degrees to the sea, leading to headlands and bays where there are bands of soft and hard rock interspersed within each other
Concordant geology
Rock outcrops are parallel to the sea, creating straight coastline, though it can create coves
How does vegetation influence the coast?
- Biological weathering
- Can create sand dunes via encouraging deposition, and then stabilise them
- Can protect and preserve coastal landforms by buffering and reducing wave energy e.g. mangroves
How does sea level influence the coast?
- Flooding, a huge issue associated with rising sea level, especially considering many urban areas are situated on the coast
- Saltwater incursion
- Creation of landforms (different depending on whether sea levels are rising or falling - remember this is different in different parts of the world)
How do people influence the coast?
- Settlements
- Fishing
- Trade
- Tourism
What is the influence of wave refraction?
Waves approach parallel to coastline. As sea shallows, waves refract. This causes energy to concentrate on headlands (due to converging waves) more than bays (due to diverging waves). Despite this headlands remain sticking out due to their harder lithology
How do cliffs and and wave cut platforms form?
- Erosion is concentrated at the base of the cliff between the low tide and high tide mark in the wave attack zone.
- This creates a wave cut notch.
- The cliff above is undercut, is therefore unsupported and collapses due to gravity.
- This creates a wave cut platform.
- Over time, this repeats and the cliff retreats inland.
How are caves formed?
Cliff surfaces are naturally made up of layers of rock called bedding planes and the joints between them are more susceptible to erosion. Joints are eroded and quickly expand, turning into larger cracks or fractures. Continued erosion through hydraulic action and abrasion will see these cracks expand
How are arches formed?
When two caves back into one another, across a headland
How are stacks formed?
Weathering processing, particularly freeze-thaw, weaken the roof of the arch until it eventually collapses leaving behind an isolated column
How are stumps formed?
A stack continues to be impacted by weathering and erosion, until it can no longer be seen at high tide
How are beaches formed?
Often form in bays, where the coast is sheltered from high-energy, erosional waves or where longshore drift provides a large supply of material
Beaches
Areas where there is an accumulation of sand and shingle caused by deposition
Spits
Long narrow beaches of sand or shingle, attached to the land at one end
Bars
Long, narrow beaches of sand or shingle across bays or estuaries
How are spits formed?
- Sudden change in coastline shape/direction
- Longshore drift has momentum and so continues to transport and deposit material at sea, following its original direction
- Over time sediment builds up creating a sandy ridge outcrop
How are tombolos formed?
When a spit connects the mainland coast to an island or wave refraction around an island cause sediment to build up
What is the distribution of coral reefs?
Between 30oN and S of the equator between the tropics
Limiting factors of coral reef formation
- Temperatures of 23-25o
- <25m deep water as sunlight needed
- Salinity
- Clean water - too much sediment obscures sunlight and clogs feeding structures
- Moderate wave action
Features of coral reefs
- Cover 1% of the ocean floor but have 25% of marine biodiversity contained within
- Composed of coral polyps that have a symbiotic relationship with algae
Biotic characteristics of the Great Barrier Reef
Coral, algae, fish, sharks, turtles, plankton, etc
Abiotic characteristics of the Great Barrier Reef
- Temperature
- Water flow
- Salinity level
- pH of seawater
- Light level
- Nutrition availability
Threats to coral reefs
- Tourism, accidental trampling, carrying capacity could be exceeded
- Industrialisation, water pollution, air pollution => rising temperatures => rising ocean temperatures => coral bleaching
- Agriculture and deforestation, increased runoff => increased siltation, fertiliser runoff => eutrophication => decline in water quality
Distribution of mangroves
- 32oN and S of the equator
- Sheltered intertidal areas that receive high annual rainfall
Limiting factors of mangrove formation
- Average temperature in coldest months above 20oC
- Fine-grained substrate or sediment
- The shores must be free of strong wave action and tidal current
- Salt water
Features of mangroves
- Trap silt to create new land
- Provides timber for building materials
- Provides protection from storms, storm surges and tsunamis
Threats to mangrove
- Timber for fuel and building material
- Aquaculture
- Land reclamation for tourist hotels and other amenities
- Diversion of fresh water
- Farming requires application of herbicides to prepare for cultivation
Distribution of sand dunes
Form worldwide at the interface between sea and land
Limiting factors of sand dune development
- Wide beach
- Lots of sand
- Obstacle e.g. marram grass
- Onshore prevailing wind
Features of sand dunes
- Plant succession on dunes
- Embryo dunes, foredunes, yellow dunes, grey dunes progression
- Mature dunes contain more humus and have a higher pH
Threats to sand dunes
Recreation e.g. trail biking, horse riding and golf courses
Distribution of salt marshes
- The intertidal zone
- Sheltered areas e.g. bays, coves and behind spits
Features of salt marshes
- Either adapted to salt water or brackish water
- Mudflats are colonised by vegetation over time, stable carr woodlands are permanently waterlogged at the back of the marsh
Threats to salt marshes
- Reclamation to create farmland and sites for industrial and port development
- Industrial pollution, agricultural pollution
- More storms, higher water levels
What are some examples of different stakeholders of coastal usage?
- Local residents
- Farmers
- Employers
- Fishermen
- Port authorities
- Transport companies
- Tourists
- Developers
- Environmental agency
What are the causes of coastal flooding?
- Storm surges - either due to an extreme high tide and low-pressure system with an onshore wind, or a hurricane
- Tsunamis - as a result of an undersea earthquake
- Climate change - isostatic readjustment, eustatic change and thermal expansion
How is flood prediction achieved?
Via assessing historical records or good levels of forecasting
What are some examples of flood prevention?
- Flood defences
- Building emergency centres
- Advanced warning systems
- Building design
- Planning new developments
- Education
How are coastal management decisions made?
With Shoreline Management Plans for each sediment cell
What are the 4 types of management?
- Hold the line
- Advance the line
- Managed retreat
- Do nothing
What are the two types of engineering?
- Hard engineering (groynes, gabions, revetments, sea walls, rip rap)
- Soft engineering (beach replenishment, cliff regrading, ecosystem rehabilitation and revegetation)
What are the problems with Holderness coast, East England (Flamborough to Spurn Point)?
- One of Europe’s fastest eroding coastlines (2m/yr)
- Geology - soft boulder clay - slumping
- Geomorphology (shape of coastline causes waves to break at the base of the cliff) and direction of longshore drift
- 29 villages lost and farmland, tourist sites and more villages (e.g. Mappleton) under threat
- Storms and sea level rise
What are the management strategies at Holderness coast, East England (Flamborough to Spurn Point)?
- Hornsea - hold the line - concrete sea wall, concrete revetment, steel gabion and timber groynes
- Withernsea - hold the line - groynes, concrete sea walls and rock armour
What are the problems with management strategies at Holderness coast, East England (Flamborough to Spurn Point)?
It impacts further down the coast
What are the problems with Sri Lanka’s coast?
- Pollution - untreated sewage
- Reclamation for tourism, housing and agriculture
- Coral reef loss due to coral “mining”, unsustainable fishing and recreational diving
- Impacts of aquaculture
What are the physical challenges with Sri Lanka’s coast?
- Coastal erosion
- Exposure to tsunamis and storm surges (link to global warming)
What are the management strategies at Sri Lanka’s coast?
- Coastal Zone Management Plan (CZMP)
- Early warning systems (prediction)
- Public education (prevention)
What are groynes?
- Narrow structures built at angles to the coastline
- They aim to slow longshore drift and trap sediment
- They can be made of timber, concrete or rock
What are (recurved) sea walls?
- Concrete walls that are placed at the foot of a cliff to prevent erosion
- They are curved to reflect the energy back into the sea
What is rip rap/rock armour?
- Large boulders are placed at the foot of a cliff or on slopes
- They break the waves and absorb their energy
What are gabions?
These are steel wire baskets filled with rocks and built into eroding cliffs to improve stability
What are revetments?
Wooden slatted barriers constructed towards the rear of beaches to protect the base of the cliffs
What are offshore reefs?
- Enormous concrete and natural blocks are sunk offshore to alter the wave direction
- Cost can be fairly high due to installation issues
What is beach nourishment/replenishment?
- Beaches are built up, usually by pumping sand onto the beach
- The source of material is usually from offshore dredging
What is cliff regrading?
Making the cliff face longer so that it is less steep
What is mangrove rehabilitation/revegetation?
Mangroves have the ability to absorb the power of waves particularly during “freak” events such as storm surges or tsunamis
What is managed retreat?
Controlled flooding of low-lying coastal areas
What are the disadvantages of groynes?
- Beaches further along the coast are starved of material due to their effect on longshore drift
- Alter usage of the beach
What are the disadvantages of (recurved) sea walls?
- Waves are still powerful and can break down and erode the sea wall
- Expensive - approximately £5000 per metre
What are the disadvantages of rip rap/rock armour?
- They look different to the geology, as the rock has been imported
- The rocks are expensive to transport
What are the disadvantages of gabions?
- Unattractive - can leave rusty metal wire on the beach
- They cannot withstand strong waves
What are the disadvantages of revetments?
- Short life span
- Unsuitable where wave energy is high
What are the disadvantages of offshore reefs?
- May be reduced by heavy storms
- Difficult to install
What are the disadvantages of beach nourishment/replenishment?
- Offshore dredging of sand and shingle increases erosion in other areas and effects ecosystems
- Can be expensive - large storms will require beach replenishment, increasing cost and needs to be done regularly
What are the disadvantages of cliff regrading?
- Not effective on its own - other defences needed at the base of the cliff
- Some houses on the cliff may need to be demolished
What are the disadvantages of mangrove rehabilitation/revegetation?
- Can restrict access to beaches
- Take up large areas of land which could be used for tourist industry
What are the disadvantages of managed retreat?
- Land is lost as it is reclaimed by the sea
- Land owners need to be compensated - this can cost between £5,000 and £10,000 per hectare
What are the advantages of groynes?
- More beach to dissipate wave energy which slows cliff erosion
- Cheap in comparison to other hard engineering methods
What are the advantages of (recurved) sea walls?
- Effective at protecting the base of the cliff
- Sea walls usually have promenades so people can walk along them
What are the advantages of rip rap/rock armour?
- Cheaper than a sea wall and easy to maintain
- Can be used for fishing
What are the advantages of gabions?
- Cheap
- Fairly effective
What are the advantages of revetments?
- Less beach material is eroded compared to the sea wall
- Cheaper and less intrusive than the sea wall
What are the advantages of offshore reefs?
- The waves break further offshore so reduced eroding power
- They allow the build up of sand
What are the advantages of beach nourishment/replenishment?
Retains the natural appearance of the beach
What are the advantages of cliff regrading?
- Cheap
- Natural - will encourage wildlife back into the area
What are the advantages of mangrove rehabilitation/revegetation?
- Provides a habitat for numerous birds and wildlife
- Popular with bird watchers and wildlife enthusiasts
- Low cost and naturally occuring
What are the advantages of managed retreat?
- This is a cheap option compared to paying for sea defences
- Creates a salt marsh which can provide habitats for wildlife and a natural defence against erosion and flooding
- Salt marshes are diverse ecosystems supporting many species
