Flashcards in Coasts Deck (29)
What are the properties of a destructive wave?
Pulls sediment off of the beach, it has a weak swash but strong backwash and is a large wave. It will commonly be found on a steep beach.
What are the properties of a constructive wave?
Builds up sediment on the beach, it has a strong swash but weak backwash and is a small wave. Will commonly be found on a gentle beach.
Describe and explain the types of weathering.
Physical weather: freeze-thaw action - Water goes into a crack in the rock, the water then freezes causing a pressure due to a 9% increase in volume and then the crack increases in size.
Biological weathering: A seed falls into the crack, rain causes the seed to grow and roots force their way further into the rock causing the rock to break up.
Chemical weathering: The natural acids in rainwater dissolve the carbonates in limestone rock causing cracks to expand.
What is the definition of weathering?
Ways that rocks are broken down in situ.
Describe and explain the types of erosion.
Hydraulic action - The compression of air in cracks puts pressure on the rock and causes pieces of rock to break off.
Corrasion (abrasion) - Sand and Pebbles are thrown against the cliff face by waves.
Corrosion (solution) - Chemicals in the water dissolve certain rock types such as chalk
Attrition - The break up of rocks and pebbles in the waves. The movement of waves means the pebbles are continuously knocked against each other, removing any sharp edges and eventually turning it to sand.
Describe soil creep (mass movement)
It is the slowest downhill movement where gravity pulls water in the soil downhill, pulling soil with it. Heavy rainfall increases the rate of soil creep. The soil appears to ripple with terracettes.
Describe slumping (mass movement)
A large area of land moving down a slope which is common on clay cliffs. Dry weather makes the clay contract and crack so when it rains water gets into the cracks, saturating the soil and pulling down a large piece of rock from the cliff face.
Explain how cliffs and wave-cut platforms are created.
The sea moves against the base of the cliff with corrosion and hydraulic action causing it to be undercut and forms a wave-cut notch. Above the notch, an overhang will be created which will fall in time by the force of gravity. This process will continue causing the cliff to retreat and regrade. The remains of the cliff will remain underneath the sea-level at high tide leaving a rocky wave-cut platform from fallen boulders. Furthermore the power of the sea will decrease as the waves have to travel further and over more friction to reach the cliff face.
Explain the creation of a stump.
A stump is formed by the action of the sea and weathering. The sea erodes a crack with hydraulic actions. As the water retreats the pressure is released breaking off pieces of rock. This makes the crack bigger, forming a cave. Eventually the cave will grow until it is an arch and when it breaks down from gravity a stack is formed. This is due to the undercutting of the sea and corrasion. The arch becomes wider at the bottom and is unstable to support the weight above. Eventually the arch is pulled down by gravity. Weathering and the sea wear down the stack until it becomes a stump.
What is longshore drift?
The movement of sediment along the shore in the direction of the prevailing wind. The swash is pushed up the beach at the same angle as the wind and the backwash is pulled straight down by gravity. This causes a 'Z' movement of sediment in the direction of the prevailing wind.
Depositional features - Beaches
Found in bays where the sea is shallower so the waves lose their energy and deposit what they are carrying. Found on straight costliness where LSD is happening. Made up of sand and pebbles. Formed by constructive waves.
Depositional features - spits
Spits are narrow, long stretches of sand and pebbles connected to the coastline at one end. They form when the coastline ends and the change in depth of the water causes the sediment to be deposited by the waves. If a river estuary is present then the meeting of the waves will cause deposition due to a change in speeds. On one side of a spit, silt and alluvium are built up forming marshes.
Depositional features - Bars
If a spit develops across a bay then it could grow all the way across linking the headlands if a gentle sloped beach is present.
What affects the rate of costal erosion?
Fetch - the longer the fetch the stronger the wave
Geology - Rock angles to the coast and rock type
Give 3 examples of the effects of coastal erosion.
Happisburgh - Fastest eroding coastline in the UK (40ft a year), 25m2 will be underwater including much farmland. 25 properties lost, including a lifeboat launching station. A Grade 1 listed church will be in the sea by 2020. On beach road the house prices dropped from 80,000 to 1 pounds. The government said the area was not cost effective but the local council began repair on the sea wall in 1995 and placed 8000 tonnes of granite rip rap in 2007.
Barton on Sea - Since 1975 it has lost: the seaside cafe which was demolished for being unstable. Manor lodge. The 2004 coastal footpath was closed and re-sited further back.
Walton-on-the-Naze - Present rate of 1.5m per year will see its listed tower fall into the sea.
Describe flood forecasting.
The Met Office predicts the likelihood of floods and posts it on their website and on the tv and radio. The Environment Agency monitors sea conditions 24/7. This storm tide forecasting service predicts coastal flooding and the information is provided on a 24/7 hotline or on their website.
Describe building design.
In Bangladesh, all one and two storey houses must have external access to the roof. Houses on the coasts of Malibu, near California are built on stilts. Houses should minimise penetration from wind, rain and storms.
Describe flood planning.
Planning permission for a house is not granted if the area is prone to flooding. The Thames flood barrier was completed in 1982. In 2010, the Environment agency installed new flood walls to protect London. In Bangladesh, the Coastal Embankment Project has led to the building of twelve sea-facing flood walls and 500 flood shelters.
Describe flood education.
The government gives advice about flood prevention risks and contingency plans on their website. In Bangladesh many coastal areas have flood warning systems. In King's Lynn in Norfolk there is a flood siren and people are employed by the council to go from house to house to warn people.
Give the advantages and disadvantages of Revetments (Hard engineering)
They are wooden slats built at the base of the cliff. They are good as they absorb wave energy through the slats, are effective for many years and are relatively cheap. They are not effective in storm conditions however, require regular maintainence and make the beach inaccessible for the tourists.
Give the advantages and disadvantages of Rip Rap (Hard engineering)
Large rocks placed in front of the cliff. They are good as they dissipate wave energy, are effective for many years and can be very cheap. They are unattractive however, are not effective in storm conditions and make the beach inaccessible to tourists.
Give the advantages and disadvantages of Recurved Sea Walls (Hard engineering)
They are good as they are visible and make residents feel safe, reflect and absorb wave energy and are effective for many years. They can cause wave scouring if not positioned correctly however, are expensive to build and are ugly.
Give the advantages and disadvantages of Groynes (Hard engineering)
They are good as they are effective for many years, keep the beach in place for tourism and prevents LSD. They disrupt natural processes however such as LSD and make walking along the beach harder and less attractive.
Give the advantages and disadvantages of Gabions (Hard engineering)
Wire cages filled with stone. They are good as they absorb wave energy and are cheaper than other forms of coastal defence (11 pounds per cage). They cages can break however and need to be secured down and are not very efficient compared to other techniques.
Give the advantages and disadvantages of Offshore Reefs (Hard engineering)
Enormous rocks and boulders are sunk offshore to alter wave speed and direction. They are good as they allow sand to build up as they decrease wave energy and cause waves to break offshore, reducing their erosive power. They are difficult to install however and may be removed by heavy storms.
Give the advantages and disadvantages of Beach replenishment (soft engineering)
It is good as it looks natural, provides a beach for tourists, a beach is the best form of natural defence and is cheap. It may affect plant and animal life in the area however, requires constant maintenance which will cause disruption for homeowners.
Give the advantages and disadvantages of Cliff Regrading (soft engineering)
It is good as it can be covered in ecomatting to encourage vegetations and is very natural - will encourage wild life. It is not effective on its own however and requires another method at the cliff foot and some homes on the cliff may need to be demolished.
Give the advantages and disadvantages of Managed retreat (soft engineering)
It is good as it creates new habitats for plants and birds as well as being very cheap. It is upsetting for landowners however and is difficult to estimate the extent of sea movement - especially due to rising sea levels.