Waves

1. Out at sea the wind tugs at the surface of the water causing the wave shape to move. Within a wave water particles move in a circular motion

2. When a wave moves into shallow water near the coast, friction causes the waves to slow at the base. Friction causes the waves to break as the top of the wave is moving faster than the bottom.

3. As the waves break onto the shore it is called the swash4. The beach will absorb the energy of the wave and then the water drains

back down the beach – this is called the backwash.

Constructive Waves

These build up the beach - deposition The swash is stronger than backwash They form gently sloping beaches 6-8 waves per minute Also known as ‘spilling waves’

Wave Action Waves are caused by the wind dragging over the surface of the water. The length of water the wind blows over is called the fetch Wave strength is determined by fetch length and time wind is blowing The stronger the wind, the longer is blows for and the longer its fetch the larger the

waves will be. The prevailing wind is the most dominant direction that the wind comes from.

The South Coasts prevailing wind comes from the South West across the Atlantic Ocean.

The Coastal Zone

Wave refraction

Waves bend when they come across resistance as they move towards the coast. As waves reach a bay, the headlands will causes friction so the waves will slow here, but in the centre of the wave they do not come across friction so they are moving faster until they hit the coast, this looks like the waves are a semicircle shape. The bending of the waves is called wave refraction.

Coastal Processes

Erosion

Longshore Drift

Longshore drift occurs when the prevailing wind occurs at the angle. The waves swash washes up the beach at an angle bringing material with it. When the waves lose

Abrasion: This is when broken rock fragments are hurled at a cliff by waves and break off more pieces of rock like sandpaper

Hydraulic Action/Power: When waves hit the cliffs and air and water are trapped and compressed into cracks. When the sea moves away the air expands, weakening the rocks and enlarges cracks

Corrosion/Solution: This is the chemical action of the sea on rocks. Salt in the seawater slowly dissolves the cliffs. The material produced is carried away by the process of solution.

Attrition: Particles carried by the wave’s crash against each other and are broken up into smaller rounder particles.

Destructive Waves

These erode material from the beach The backwash is stronger than swash High steep waves Steeply sloping beaches 13-15 waves per minute Also known as ‘plunging’ waves

energy the backwash brings the material straight back down the beach under the influence of gravity. In this way material is moved along the coast in a zigzag fashion.

Deposition

Deposition occurs when waves lose their energy. This normally occurs in bays or when waves lose their energy due to friction from the sea bed.

Weathering

Weathering is the breakup or decay of rocks in situ at or close to the earth's surface. Weathering occurs above the high tide water mark on the cliffs at the coast. There are three types:

1. Biological – this is weathering caused by living organisms such as trees roots or burrowing animals breaking apart the rocks or cracks.

2. Mechanical – this is weathering that does not involve chemical change e.g. free-thaw

3. Chemical – this is weathering that involves a chemical change taking place. Rainwater picks up CO² and this becomes a week carbonic acid. This reacts with calcium carbonate in chalk or limestone. Or some rocks just dissolve like sugar does in water.

Freeze-thaw weathering (Mechanical)

Water repeatedly freezes and thaws in cracks or holes in the cliff. Water will expand by approx. 9% and if it’s confined in a small space this stresses the rock and widens and deepens cracks. Rocks may break apart and fall to the bottom of the cliff and collects as scree.

Erosional Landforms

1. Wave Cut Notch

1. Caves, Arches and Stacks

2. Headlands and Bays (Discordant)

3. Headlands and Bays (Concordant)

1. Waves attack the cliff between the high tide and low tide mark will cause a wave-cut notch to be formed at the bottom.

2. As the notch grows inland the cliff above creates an overhang. Eventually the cliff collapses and the debris is then removed by the sea. This process means the cliff face gradually retreats and creates a wave cut platform

1. Headlands are formed when the sea attacks a section of coast consisting of alternating bands of hard and soft rock.

2. Less resistant rock erodes quickly to form bays

3. More resistant rock protrude to form headlands

1. Bays can also form when there are alternate bands of hard and soft rock that are parallel to each other

2. Hydraulic action creates cracks in soft rock and will create a cave in the cliff. This erodes deeper and further wave action occurs due to wave refraction carving out a bay behind the rock. An example of this is Lulworth cove, in Dorset.

4. Caves, Arches and Stacks

Wave energy is concentrated on headlands because they jut out to sea. Cracks are pounded by the sea via hydraulic action and abrasion creating caves. When these erode through the headland they create arches, which eventually collapse leaving a stack. When this collapses it creates a stump.

Depositional Landforms

1. BeachesConstructive waves help build beaches by depositing material when waves lose energy.

2. Spits

Longshore Drift moves material along a coastline in the direction of the prevailing wind.

Deposition occurs at the bend of a coastline where it changes shape.

Deposited material may accumulate away from the coast into the open sea until a long ridge of sand is built up

If winds come from the opposite direction the end of the spit may become recurved like a hook

This may also occur where a river meets the coast and a salt marsh may develop behind the spit as it is sheltered.

a) Smallest material is deposited nearer the sea

b) Heavier material is deposited further up the beach

c) The natural ridge on the beach is known as the berm.

3. Tombolos

Tombolos are formed when a spit continues to grow outwards joining land to an offshore island. e.g. Chesil Beach joins the South Dorset coast to the Isle of Portland.4. Bars

A bar is formed when a spit joins to headland. A Lagoon will form behind if there is a small river flowing into it. An example is Slapton Ley in Devon.

Hurst Castle Spit

Hurst Castle spit is on the Hampshire coast close to the city of Southampton. Henry VIII built a castle near the top of the spit to help defend England from possible invasions. Behind the spit is Keyhaven marshes a Site of Special Scientific Interest (SSSI).

Shoreline Management Plans (SMPs)

The coastline of England and Wales has been divided into a number of self-contained sediment cells. The SMP has been developed for each area, which details the natural processes, environmental considerations and human uses.

Hold the line: This means taking action to keep the line of the coast as it is now e.g. sea wallAdvance the line: This means to put in greater protection by increasing the size of the beach for example.Managed retreat:

Allow the land to flood and erode. This option can be taken if the land is of low value and it would cost more to protect it than what it is worth. A cost benefit analysis would help make this decision.

Coastal Management

Successful management of coastal areas depends on understanding the

differing interests of those who want to use coastal land in different ways.

Hard Engineering schemes are made using concrete or steel. They are manmade and usually cost a lot to build. They work against natural processes.

Soft engineering schemes work with natural processes and usually are cheaper. They look natural but don’t last as

long as hard engineering schemes.

Case Study: Holderness Coast - Mappleton

Mappleton is a small village which by 1990 was under threat of becoming lost to erosion. It is located on the Yorkshire coastline between the Humber estuary and Bridlington. The B1242 is a vital link road along the coast and it would have been too expensive to find a new route for it. The government therefore spent £2 million pounds trying to save the village

Slumping

If cliffs are made of sand or clay they are prone to slumping. If a cliff has a layer of clay with sand on top, rain water will seep down though the layer of sand and then saturates the base of the sand

ISSUES

Coastline is 3-4km further inland than in Roman times. 29 villages lost to sea in past thousand years. Erosion occurring at 2m per year – the fastest eroding coastline in Europe

SOLUTIONS

2 rock groynes were built from Granite imported from Norway.

IMPACTS

Groynes have reduced longshore drift and stopped coastal erosion at Mappleton but have caused problems further south

Cliffs are no longer protected by a beach and at high tide waves reach the base of the cliff increasing the rate of erosion to 10m a year! Remember Sue Earle’s farm!

CAUSES

Cliffs made of unconsolidated Bolder Clay and sand which are easy to erode.

Winds from North and North East causing erosion due to large fetch

Longshore drift occurs from North to South along the Holderness Coast

between this layer and the clay layer. This reduces friction and causes the sand to be unstable and move down slope due to gravity as large chunks. With clay cliffs, they dry out and crack in summer. When it then rains water seeps down the cracks and make the cliff unstable so it then slumps downwards.

Sea Level Rise There are two ways that sea levels change:1. The sea level changes itself globally = Eustatic2. The land changes locally = Isostatic

1a) Melting global ice is due to warming temperatures means sea levels rise as there's more water in the sea. Decreasing world temperatures = ice, which means lower sea levels as the water is stored as ice.

1b) If global temperatures increase the seas get warmer. This means that the water expands so the sea level rises = Thermal Expansion

2a) Isostatic rebound/uplift: This is where ice melts on the land, so the weight on the land disappears so the land rises like a sponge would after being compressed. When Scotland had ice on it, it sank due to the weight, so sea levels looked like they rose and the south of England rose so the sea level looked like they got lower. Its like a sea saw.

2b) When an earthquake happens, the land changes and can be forced up or down, so this means that sea levels can look either lower or higher. e.g. After the 2004 earthquake parts of Indonesia were raised by 6 metres

2c) When rivers meet the sea at the mouth, the land is flatter. This means that the water loses its energy and deposition occurs. This means that sediment builds up so the level of the river changes and rises.

Consequences of sea level change - Coastal flooding in Norfolk

Over the last 15 years global average sea levels have risen by 3mm a year. This could increase by 28-43cm by the end of this century!

London flooding

If The Thames Barrier failed and London flooded these are consequences:- London is world centre for the banking and

finance industry. It creates 40% of the UK's GNP.

- Insurance industry would have huge claims being made for damaged property.- Transport networks would be flooded including over-ground and tube networks. - London's population is approximately 7.5 million- Power and water supplies affected- Historic buildings would be flooded e.g. Houses of Parliament- London makes £16 billion from tourism every year

Cost Benefit Analysis

The cost benefit analysis looks at whether a scheme is worth putting in place for the amount of property or business it will protect. You divide the cost of property by the cost of the defence (lasting for 100 years). The higher the value the most cost effective the method is.

Salt Marshes

Limitations:

Uses the average cost of a defence method and average cost of property

Roads are not taken into account for the value of the land a scheme would protect

Pioneer plant: the first plant species to colonise an area that is well adapted to living in a harsh environment e.g. salt tolerant

Vegetation succession: a sequence of vegetation species colonising an environment

Keyhaven Marshes

These marshes are in the lee of Hurst Castle spit in Hampshire. It supports a range of habitats including grassland, scrub, salt marsh and reed beds. This variety of habitats accounts for a rich diversity of wildlife in the area. Examples include: Cordgrass, sea lavender, Oystercatcher and Ringed Plover (birds), Common Blue butterfly and the Wold spider.

It is under threat because: a) The marsh is retreating by up to 6m a year. It is being squeezed between

the low sea wall and the encroaching sea.b) The spit is being breached during severe storms. The 1989 storm exposed

50-80m of the spit to the sea and it was eroded in less than 3 months. c) More people are visiting the marshes. They trample on the marshes, moor

boats in the creeks and causes pollution. How are Keyhaven marshes being managed in a sustainable way?

1. In 1996 rock armour and beach nourishment were used to increase the height and width of the spit to try and stop it being breached. £5 million was spent on this and since then the spit has not been breached and the marshes seem safe

2. The marshes have been made a Site of Special scientific Interest (SSSI) and part of it is now a National Nature Reserve. This has been done to protect the wildfowl and wading birds and so that the area can be carefully monitored and managed to main the rich biodiversity. Access is limited and development restricted.

3. In the future the low sea wall may be removed and the land allowed to flood if sea levels continue to rise.