Waves- how are they formed and how do they affect the coast?

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1 Question 7 Coasts Waves- how are they formed and how do they affect the coast? Waves are caused by friction between the wind and water causing the water to swell. The size and energy of a wave is influenced by: how long the wind has been blowing the strength of the wind how far the wave has travelled (the fetch) Swash: The wave breaking on the beach Backwash: The wave going back out to sea under the force of gravity. Prevailing wind: The most common wind direction. Constructive Waves Destructive Waves They are created in calm weather and are less powerful than destructive waves. They break on the shore and deposit material, building up beaches. They have a swash that is stronger than the backwash. They have a long wavelength, and are low in height. Destructive waves are created in storm conditions. They are created from big, strong waves when the wind is powerful and has been blowing for a long time. They occur when wave energy is high and the wave has travelled over a long fetch. They tend to erode the coast. They have a stronger backwash than swash. They have a short wave length and are high and steep.

2 Coastal processes- weathering When rocks and surface materials are broken down through the actions of the atmosphere we call it weathering. Weathering weakens rocks at the coast and makes them more likely to be affected by mass movement and erosion It is a sub aerial process Chemical: when weak acids for example rain dissolves the rocks. Physical : Freeze thaw weathering- due to temperature, frost, water etc. freeze thaw weathering is when the constant freezing of water and then melting again causes cracks in the rocks. Biological: when rocks are broken up by living things e.g. plant routes or burrowing animals. Coastal Processes - Erosion Hydraulic action. Air may become trapped in joints and cracks on a cliff face. When a wave breaks, the trapped air is compressed which weakens the cliff and causes erosion. Abrasion. Bits of rock and sand in waves grind down cliff surfaces like sandpaper. Attrition. Waves smash rocks and pebbles on the shore into each other, and they break and become smoother. Solution. Acids contained in sea water will dissolve some types of rock such as chalk or limestone Coastal Transport Traction: Pebbles and larger sediment are rolled along the sea bed. Saltation: Load is bounced along the sea bed, eg small pieces of shingle or large sand grains. Currents cannot keep the larger and heavier sediment afloat for long periods. Suspension: Small particles are carried in water, eg silts and clays, which can make the water look cloudy. Currents pick up large amounts of sediment in suspension during a storm, when strong winds generate high energy waves. Solution: Minerals are dissolved in sea water and carried in solution. The load is not visible. Load can come from cliffs made from chalk or limestone, and calcium carbonate is carried along in solution. Coastal Deposition When the sea loses energy, it drops the beach material / sediment, rock particles and pebbles it has been carrying. This is called deposition. Deposition happens when the swash is stronger than the backwash and is associated with constructive waves. Deposition is likely to occur when: waves enter an area of shallow water. waves enter a sheltered area, eg a cove or bay. there is little wind. there is a good supply of material

3 Longshore Drift - Transport The continual swash and backwash that carries material along the coast is called longshore drift. Mass Movement Headlands and bays Landforms from Erosion Soft rock Hard rock Found when you have alternating bands of hard and soft rock such as clay between limestone and chalk. As the waves attack the cliff the soft rock such as clay erodes faster. This forms a horse shoe shape in the cliff called a bay. You find headlines on either side of the bay. Cliff erosion and wave cut platforms Cliffs and wave-cut platforms The process of cliff erosion. 1. Weather weakens the top of the cliff. 2. The sea attacks the base of the cliff forming a wave-cut notch through abrasion and hydraulic action. 3. As erosion continues the notch increases in size undermining the cliff. This causes the cliff to collapse. 4. The backwash carries the rubble towards the sea forming a wave-cut platform. 5. The process repeats and the cliff continues to retreat. 6. Wave cut platforms. Wave cut platforms are the platforms at the bottom of a cliff, formed during cliff erosion.

4 Caves, arches, stacks and stumps. Hydraulic action is the principle process taking place here. The water works its way in through a crack in the cliff, and over a period of time a cave is formed due to continued erosion (hydraulic action and abrasion.) When the cave breaks through to the other side of the headland it becomes an arch. Eventually, the top of the arch will be undermined and collapse forming a stack. The base of the stack will continue to be eroded until it collapses to forma stump. For this process: Tell the story of the feature requested plus all the features before. For example a Stack = Crack>Cave>Arch>Stack Landforms from deposition: Beaches: formed from the deposition of eroded material from elsewhere along the coastline. Spits: 1) Longshore drift moves material along the coastline. 2) There is a sharpe change in direction of the coast e.g. river or bay. 3) A spit forms when the material is deposited. 4) Over time, the spit grows and develops a hook if the prevailing wind changes direction. Waves cannot get past a spit, which creates a sheltered area where silt is deposited and mud flats or salt marshes form. Bars (lagoon): A spit that extends from headland to headland. The water trapped behind forms a lagoon. Salt marshes: often formed in the sheltered area in a spit or a bar.

5 Mass Movement Rocks loosed by weathering move down a slope under the influence of gravity. The rocks can slide or slump Sliding Large chunks of rock slide down a slope quickly without warning. This can make it very dangerous to walk along the cliff. Slumping Common where cliffs are made from clay Clay becomes saturated during heavy rainfall The extra weight/pressure acting on the cliff causes it to move. The clay flows down towards the sea as part of a mud or debris flow As it moves it rotates About CASE STUDY: The impact of rising sea levels: The Maldives Located in the Indian Ocean Small country made up of over 1000 islands Lowest Country in the world Highest point is 2.4 metres above sea level Ideal holiday destination with 30% of GDP coming from tourism What is happening? Sea level is rising between 30cm and 1.4m over the next 100 years Temperatures rise therefore: Polar ice sheets are melting along with mountain glaciers Water is getting in oceans is getting warmer and expanding

6 Impacts on the Maldives Coral reefs will die as they bleach due to deep water and lack of sunlight Ecosystem connected to reefs will die out - marine life 400,000 people forced out of homes environmental refugees Will need international aid to cope with the rise in sea levels Global Impacts of global warming 100million people will be displaced. Many small islands in the Indian and Pacific Oceans will be lost under water. Netherlands is at risk because 27% of the nation is below sea level. Cities like London and New York will have to spend billions on flood defense schemes. Jobs in the tourist industry will be lost and will be hit by mass unemployment. Younger generation will leave the Maldives. Places like the Fens in England could be lost. Risk that entire Island chain will be lost under water. CASE STUDY: The impacts of cliff erosion, Christchurch Bay. Key Facts South Coast of England, near Bournemouth. Eroding at a rate of 1-2 metres per year. 16km stretch of coastline. Difficult to protect it all. Tourism is big business and provider of jobs. Densely populated with resorts such as Barton-on-sea. Why is it eroding rapidly? 1- Marine processes weaken base of cliff. Hydraulic action and abrasion. 2- Sub aerial processes attack cliff top weathering, slumping, sliding. 3- Geology- permeable sand lies on top of impermeable clay and is saturated during heavy rains. This can make cliff top heavier and unstable. 4 - Fetch, 3000 miles distance as waves travel across the Atlantic gaining destructive power from the prevailing wind. 5 - Human activity- building, walking and tourist activity. Christchurch bay is a honey pot attraction. Impacts Social Homes close to the cliff go down in value and are uninsurable. Often worth only 1 Insurance companies refuse to cover coastal erosion because it is an act of god or charge high premiums. Risk of loss of life due to sudden erosion/sliding of homes or walkers along cliff top. People lose homes if they fall into the sea. environmental refugees

7 Economic - Impacts Roads and railways under threat and need protecting at great expense or rerouting. Tourists may be put off due to danger or lose of key attractions therefore it would lead to a decline in business for shops, cafes and hotels. Barton Golf Course has had to be expanded inland to protect the green and rebuild after cliff erosion. Environmental - Impacts Cliff collapse makes the area look unattractive and damage to buildings can leave materials littering the coastline. Some areas are eroding but are not protected because they are areas of special scientific interest. Bird nesting sites and green land are being lost. Coastal Management Britain's coastline is falling into the sea, as a result many areas are protected by sea defences. There are two main forms of coastal Management, hard engineering and soft engineering. Type of defence - hard engineering Building a sea wall A wall built on the edge of the coastline. Pros and cons Advantages Protects the base of cliffs, land and buildings against erosion. Can prevent coastal flooding in some areas. Strong and durable. Made of reinforced concrete. Building groynes A wooden barrier built at right angles to the beach. Disadvantages Expensive to build. 10k per metre. Curved sea walls reflect the energy of the waves back to the sea. This means that the waves remain powerful. Over time the wall may begin to erode. The cost of maintenance is high with the wall having to be replaced every years. Advantages Prevents the movement of beach material along the coast by longshore drift. Allows the build up of a beach. Beaches are a natural defence against erosion and an attraction for tourists. Disadvantages Can be seen as unattractive as they are unnatural features at right angles. Costly to build and maintain, 100k per groyne. Wooden groynes will rot over time.

8 Rock armour or boulder barriers Large boulders are piled up on the beach. Advantages Strong rocks such as granite absorb the energy of waves. Allows the build-up of a beach a natural defence. Disadvantages Can be expensive to obtain and transport the boulders. Cost 1500 per metre. Have to be transported from places such as Norway. Soft engineering (Beach nourishment, Dune regeneration, Marsh creation, Managed retreat) Beach replenishment This replaces beach or cliff material that has been removed by erosion or longshore drift. The main advantage is that beaches are a natural defence against erosion and coastal flooding. Beaches also attract tourists. It is a relatively inexpensive option but requires constant maintenance to replace the beach material as it is washed away. Managed retreat Areas of the coast are allowed to erode and flood naturally. Usually this will be areas considered to be of low value - eg places not being used for housing or farmland. The advantages are that it encourages the development of beaches (a natural defence) and salt marshes (important for the environment) and cost is low. Managed retreat is a cheap option, but people will need to be compensated for loss of buildings and farmland. Alkborough flats tidal defence scheme Location Humber Estuary, Lincolnshire, 440 hectares of agricultural land on the south bank of the River Humber Why does Alkborough need a flood scheme? The effects of climate change are expected to increase high tide levels in the Humber Estuary 300,000 people who live in the area and are at risk of flooding.

9 What are they doing to reduce flood risk? The Environment Agency took charge to protect the area. Opened in September 2006 and is one of the largest flood storage schemes in Europe. It allows flood water from the Humber estuary to spill out of the river during the highest tides to fill the low lying land. By flooding the Alkborough flats they protect places such as Hull. The site s capacity is so great that it could reduce high tide levels in the upper estuary by as much as 150mm -15cm. It is a way of managing rising sea levels through soft engineering It has been designed by the Environment Agency to: The Environment Agency took charge to protect the area. Opened in September 2006 and is one of the largest flood storage schemes in Europe. It allows flood water from the Humber estuary to spill out of the river during the highest tides to fill the low lying land. By flooding the Alkborough flats they protect places such as Hull. The site s capacity is so great that it could reduce high tide levels in the upper estuary by as much as 150mm -15cm. It is a way of managing rising sea levels through soft engineering Coastal habitats: Studland bay nature reserve Location: Dorset, England along the South Coast. Near Swanage. 1.5 million visitors each year. Grass covered dunes, heath and scrub. It is managed by the National Trust. Habitats Sand Dunes develop as the wind deposits sand on low lying areas forming hills. Dunes grow around obstacles such as driftwood. Unique ecosystem marram grass and Lime grass close to shore and heather further inland. Marram grass holds the dunes together. It is the richest 1000 hectares for butterflies, wildlife, birds in the country. Ecosystem- the relationship between plants. animals and the environment. Key problems Increase in tourists and cars. Vegetation is vulnerable and takes years to establish. if it is destroyed then the ecosystem will collapse. Home to rare species of plants and birds that could be lost forever. e.g. Dartford Warblers and Sand Lizards.

10 Key problems- continued Beach gets overcrowded and littered by tourists. Visitors need somewhere to park and can park on the verge damaging the area. Visitors also require additional facilities such as paths and toilets. As a result more space is given over to development with habitat lost forever. Visitors litter and cause fire hazards with BBQ's and cigarettes ends. Solutions Marram grass planted to stabilise the dunes and areas fenced off to allow it to grow. Bird watching hides constructed so animals can be viewed without disturbing them. Car parking spaces have been controlled and limited and vehicles have been banned from the beach. Fire beaters placed in the dunes to control risk of fire. Boardwalks laid and signs placed to educate tourists and prevent footpath erosion.