- Created by: naomi
- Created on: 12-04-12 17:25
Wave Size and energy. Two types of wave
- Waves are made when wind blows over the surface of the sea, creating friction.
- The size and energy of the wave are greatest when the wind is strong, has been blowing for a long time, and has come a long way.
There are two types of wave: Constructive and Destructive
- Are longer and flatter
- Happen in calm conditions
- Have strong swash which carries material up the beach.
- They create shallow beaches.
- Taller and shorter in length
- Happen in more stormy weather
- Have a strong backwash which erodes material from the beach.
Fetch = How far the wind has travelled.
Waves are responsible for most of the erosion along coasts. Wind blowing over a smooth sea surface causes small ripples which grow into waves.
When a wave approaches the coast, it's lower part is slowed by friction but the upper part continues to move forward.
As it is left unsuported, it topples over and break forward against the cliff face, or surges up the beach. the waves that erode most are called destructive waves.
Mass movement is when rocks loosened by weathering move down the slope under the influence of gravity. The rocks can slide or slump.
There are FOUR types of erosion and transport
Erosion: caused by destructive waves, wearing away the coastline. It happens when the waves are packed with ENERGY. Erosion destroys landforms
- Corrasion/Abrasion is caused by large waves hurling beach material against the cliff, chipping and grinding it down
- Attrition is when waves cause rocks and pebbles to bump into eachother and break into smaller pieces
- Corrosion/Sollution is when salts or acids in sea water slowly dissolve a cliff
- Hydraulic action is the explosion of compressed air in cracks. The pressure of the compressed air weakens the rock and forces it to break up.
Transport: is the movement of material in the sea and along the coast by waves.
- Saltation is the movement of hard particles over an uneven surface in a turbulent flow of water
- Traction is where material is rolled along the bed of the sea.
Weathering and Erosion of Cliffs
- Waves attack the base of the cliffs but the cliff face is likely to be eroded by weathering rather than by the sea itself.
- In resistant rocks such as limestone and chalk water can get into cracks and fissures in the rock and widen them by chemical action or through freeze - thaw. Less resistant rocks can become waterlogged, causing landslips.
- Weathering = Breaks it down and leaves it Erosion = Takes it away.
Hard rock cliffs such as chalk or limestone
Cliffs formed from hard or resistant rocks such as chalk or limestone are eroded slowly. The cliffs are often high and almost vertical and erosion by the sea at the base of the cliff can cause rock falls.
Soft rock cliffs such as sands and clay
Less resistant rocks such as sands and clay are more easily eroded and are usually lower in height. Cliffs formed from sands and clay are eroded at the foot by the sea but the cliffs themselves can become waterlogged by rainfall. This causes them to become unstable leading to land slips, also called rotational slumping.
Coastal Defences: Soft Engineering
Cheaper and do not damage the appearance of the coast. It is a more sustainable approach to coastal protection. However, they are not as effective as hard engineering methods.
- Beach nourishment: Sand is brought in to build up the beach, either from further along the coast or from offshore. This looks completely natural and provides a beach to protect the coast and for visitors to enjoy. However, the sea will continue to erode the beach so replenishment has to be repeated every few years.
- Dune nourishment: Sand dunes provide food natural protection for the coast. Dunes may be damaged by storms or by visitors walking through them to get onto a beach. This protects the environment as well as reducing the risk of flooding and erosion.
- Managed retreat: In some places the sea is being allowed to erode the coast and people and activities have to move away. This is clearly the cheapest solution but it is very disruptive for the people who live where land and buildings are likely to be lost. In many cases compensation is not paid so individuals can lose a great deal of money.
Coastal Defences: Hard Engineering
These structures are very expensive to build and maintain and are only used when towns, villages or expensive installations are at risk.
- Groynes: At seaside resorts wooden walls or groynes are built across the beach to stop the sand being washed away by longshore drift. This may cause problems elsewhere.
- Sea walls: The most effective method of halting sea erosion. Made of concrete, they are curved to deflect the power of the waves. Sea walls may be unsightly and also can restrict access to the beach.
- Revetments: Sloping wooden fences with an open structure of planks to break the forces of the waves and trap beach material behind them.
- Gabions: Less expensive than a sea wall or a revetment, they are cages of boulders built up at the foot of a cliff or on a sea wall.
- Rip rap: The cheapest method but still expensive. Piles of large boulders are places on the beach to protect the cliffs from the full force of the sea.
- Offshore breakwaters: These are built on the sea bed a short distance from the coast and are usually made from rock or concerete. They are also very expensive to build but are effective because the waves break on the barrier before reaching the coast.
Sea wall curve = Less scouring
Coastal Management Case Study: The Holderness Coas
In 2002 an integrated coastal zone management plan was produced foro Holderness. This combines the use of hard engineering to protecct some places with not protective other palces at all. This managed retreat means the unprotected areas will eventually disappear completely.
Mappleton is a small village which lies about 3km south of Hornsea on the Holderness Coast. Mappleton was at risk of being lost to the sea because the coast was eroding it so quickly. The coast consists of boulder clay which was deposited by glaciers during the ice age. It is a soft unconsolidated rock which i easily eroded both by the sea and weathering.
Two large rock groynes were built, together with a rock revetment along the base of the cliff. 60,000 tonnes of granite blocks came from Norway. The groynes interrupt longshore drift, which carries sediment along the coast in a southerly direction. The revetment prevents cliff-foot erosion, protecting Mappleton. The rate of erosion south of the groynes has increased significantly because sediment being carried south is trapped by the groynes. This means that there is no beach to protect the cliffs to the south which are now eroding at a fast rate than before.
Waves and Deposition
The material eroded from cliffs by the sea is worn down by the process of attrition and is moved by the sea to be deposited further along the coast. The sea moves material by longshore drift. Over the course of a year the movement of sediment will depend on the direction of the prevailing wind. On Britain's south coast the prevailing wind is from the southwest; this means longshore drift moves material from west to east.
- Swash brings material up the beach at an angle
- Backwash moves material straight back down the beach to the sea
- Material is picked up by the next wave and moved along the beach
- Material is moved along the beach by the movement called longshore drift.
Features created by longshore drift:
- Spit - if the spit reaches right across the mouth of a bay, a sand bar is formed and the trapped water is a:
- Lagoon - the water behind a spit or a sand bar slowly silts up with material from streams. Where it is shallow, plants will grow and new land will form.
Mechanical and Chemical Weathering
- This leads to the breakdown of rock without any change in the minerals that form the rock.
- The type varies with climate
- In cold climates the most widespread type is frost shattering or freeze thaw. - the volume of water expands when it freezes = expands within a crack or joint in the rock = more pressure is put on the surrounding rock = crack widens.
- This happens when the rock's mineral composition is changed, leading to the disintegration of the rock.
- Granite is one type of rock that is vulnerable to chemical weathering
- Feldspar = one of the minerals that make up granite and is converted into clay minerals such as haolin.
Maldives and rising sea level
The causes of sea level rise:
- As the sea water is warmed it then expands. This means it is taking up more space and so sea level rises.
- Ice caps and Glaciers are melting. This is ice up on the mountain, as as it melts it flows into the sea. This is likely to cause 10-12cm of seal level rise in the 21st century.
- Loss of land ice in Greenland and Antarctica is due to the ice melting. It will also follow into the sea and cause it to rise.
The effects of sea level rising in the Maldives:
- Tourism is the islands' biggest earner. If resorts are flooded and beaches destroyed or people stay away they will be affected economically.
- Fishing earns the country money and feeds the population. Rising sea levels threaten coral reefs and its ecosystem and so have lowered fish numbers in the area
- Politically it puts the government under a lot of pressure to sort it out. In feb 2012 the president was removed in a coup. People will be forced to migrate to another country eventually.
Managing the Unique Ecosystem at Lulworth
All affect the conditions for plants that make this area have a unique habitat:
- Porus chalk
- Thin siol
- Salt from the sea
Ways in which people are managing the unique ecosystem:
- Rebuilding footpaths
- Visitor surveys
- Surveys of wildlife
- Education and information
- Traditional farming
- Litter picking
Land Use conflicts and the problems they cause
Land use conflicts:
- Army - Scares animals and wildlife
- Farming - Land pollution
- Tourism - disrupts nesting animals and wildlife
- Residential - Land pollution - disrupts habitats etc
How does the ecosystem management try to overcome these problems?
- AONB, SSSI, WORLD HERITAGE SITE.
- Army - The noise is not regular and is far away.
- Farming - They only use the land for grazing and no industrial farming.
- Tourism - Use money from tourist income to place pathways and fences. Also employ people for the education centre to raise awareness about the ecosystem.
- Residential - Kept to a minimum
Sustainable Ecosystem Management at Lulworth
- They do not use hard or soft engineering, and so lets the erosion happen naturally at its own speed.
- They only build on brownfield sites and make sure any of the wildlife e.g. plants they disturb is put back.
- They ensure that visitors stick to the paths made, and so do not harm the environments or the animals and wildlife.
- They don't restrict any areas complete, as no one would go there.
- Money raised from the car park goes towards the ranger's wages
- The rangers are paid for education purposes - educating people about the ecosystem so they treat the area well.
- Cut back shrubs or burn it to leave space for other plants.
- Use own rock to build etc. (which is the local limestone).
- Pastoral farming
- No arable crops which would be unsustainable as the chemicals would harm the area.