Coastal Landscapes

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WAVE TYPES AND THEIR CHARACTERISTICS

How do waves form?

Waves are formed by the wind blowing over the sea

Waves are formed from energy transfer by the wind

Friction with the surface of the water causes ripples to form and these develop into waves.

The longer the fetch, the more powerful the wave

Waves can also be formed more dramatically when earthquakes or volcanic eruptions shape the land; these are called tsunamis

What are waves?

Waves are a disturbance on the surface of the sea or ocean in the form of a moving ridge or swell

What happens when waves reach the coast?

Only when waves approach the shore is there forward movement of water as waves break and surge up the beach.

The seabed interrupts the circular movement of the water

As the water becomes shallower, the circular movement becomes more elliptical

This causes the crest of the wave to rise up and eventually to collapse onto the beach

The water that rushes up the beach is called swash

The water that flows back towards the sea is called backwash

Constructive waves

Constructive waves build beaches

They have a long wavelength and a low frequency

Typically found in sheltered bays and spits

Calmer weather conditions when less energy is transferred to the water

These are low waves that surge up the beach and 'spill' with a powerful swash

They carry and deposit large amounts of sand and pebbles and 'construct' the beach making it more extensive

These waves are formed by storm often hundreds of kilometers away

Destructive waves

Destructive waves destroy beaches

They have a short wave length and a high frequency

Found in more exposed areas

These are formed by local storms close to the coast, and they can 'destroy' the beach

The are closely spaced and often interfere with each other, producing a chaotic swirling mass of water

They become high and steep before plunging down onto the beach

There is little forward motion (swash) when a destructive wave breaks but a powerful backwash

This explains the removal of sand and pebbles and the gradual destruction of the beach

What does a wave's energy depend on?

Strength of the wind

Length of time the wind is blowing for

Fetch

Which are of the UK experiences the most powerful waves? Why?

The South West. This is because the wind is stronger as it has blown for longer over a greater distance which means it has a bigger fetch. This produces waves which have huge amounts of energy

Compare the characteristics of constructive and deconstructive waves

Constructive and deconstructive waves have different characteristics that impact coastlines. Constructive waves are low energy, with a strong swash and weak backwash, which deposits sediment and builds up beaches. In contrast, destructive waves are high energy, with a weak swash but strong backwash, which erodes beaches and removes material. Constructive waves create gently sloping beaches while destructive waves form steep beaches due to their erosive power.

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KEY WORDS:

Fetch: the distance that wind has blown across the water

Coast: where the land meets the sea

Swash: when a wave breaks, water rushes up the beach; on most beaches swash approaches at an angle

Backwash: water then runs back down the beach, back out to sea under the force of gravity; then the backwash pulls the wave back from the beach at a 90 degree angle

Constructive waves: waves that deposit sediment onto the beach

Destructive waves: waves that remove sediment from the beach

Weathering: the break down of rock, mainly caused by weather conditions, no movement of the rock is involved

Porous: contains holes

Permeable: allow water to pass through

Mass movement: the movement of cliff material caused by erosion, weathering and gravity

Coastal erosion: the removal of material from the coast by waves, tidal currents and/or activities of humans causing the retreat of coastlines

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WEATHERING AND MASS MOVEMENT

What causes cliffs to collapse?

This is because of different types of weathering

This is the decay or weakening of rocks in their original place on, or close to, the ground surface.

It is mostly cause by weather factor such as rainfall and changes in temperature

Mechanical or physical weathering:

The disintegration of rocks in situ

Most common on coasts (freeze-thaw, salt crystallization)

Freeze-thaw weathering occurs when rocks are porous or permeable. Water enters the rock and freezes. The ice expands, putting pressure on the rock until it cracks. Repeated freeze-thaw can cause the rock to break up (salt weathering has the same principles)

Rock fragments are called scree

Biological weathering

Involves the roots of vegetation, causing the breakup of rocks

Both plants and animals can have an effect on rock

Roots or animals can burrow into the rock, weakening the rock structure until it breaks away

Chemical weathering

Rainwater and sea water can be a weak acid

Overtime a coastline made up of rocks such as limestone or chalk can become dissolved by the acid in the water

Carbonation is an example of chemical weathering. Rainwater absorbs CO2 from the air and becomes slightly acidic. Contact with alkaline rocks such as chalk and limestone produces a chemical reaction causing the rocks to slowly dissolve.

Oxidation is when rocks are broken down by oxygen and water

Mass movement

Mass movement is the downhill movement o cliff material under the influence of gravity.

Rockfall: involves rock fragments breaking away from the cliff face, often due to freeze-thaw weathering.

Landslides: In areas of more resistant cliff material, erosion is greatest when waves break at the foot of a cliff. This causes erosion at the base of the cliff. This creates a wave cut notch in the base of the cliff. As the notch increases in size, the weight of the cliffs above becomes too much support, leading to a landslide. This material will provide temporary protection for the cliff behind. However, once the sea has removed it, this process will occur again. Wave-cut platforms will be created where cliffs are made of more resistant material.

Slumping/rotational slip

Cliffs formed from boulder clay, materials deposited by glacial periods, are suspectable to high rates of coastal erosion. The soft boulder clay is quickly eroded away through hydraulic action and abrasion. However, this is not the only way it is being eroded. Sub-areal processes, such as rainfall, cause erosion. This often happens when layers of boulder clay, left behind by melting glaciers, becomes saturated, causing the cliff to slump.

The soft boulder clay holds rainwater and runoff

Waves erode the base of the cliff creating a wave-cut notch. The clay becomes saturated and forms a slip plane

The weight of saturated cliff causes it to slump

Mudslides

Mudslides occur when saturated soil and weak rock flow down a slope

Typically occur where cliffs are made from boulder clay

Describe the effects of weathering and mass movement on a cliffed coastline

Weathering and mass movement significantly affect cliffed coastlines, causing erosion and reshaping the landscape. Weathering processes, including mechanical (freeze-thaw and salt crystallization), chemical, and biological weathering, work in situ to weaken the cliff structure. This creates cracks and fissures, making the rock more suspectable to erosion and producing loose material. Mass movement processes, driven by gravity, include rockfall, landslides, slumping and mudflows. These cause rapid cliff retreat and deposit large amounts of material at the cliff base. For example, slumping at Walton on the Naze has led to significant coastal erosion and land loss. The combined affects of weathering and mass movement result in cliff instability, retreat of the coastline, and the creation of distinctive coastal landforms. While the deposited material can temporarily protect the cliff base from wave erosion, overall, these all contribute to the ongoing erosion and reshaping of cliffed coastlines

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COASTAL EROSION PROCESSES

What is coastal erosion?

The wearing away of the land by the sea, often involves destructive waves wearing away the coast

What are the processes of coastal erosion?

Corrasion: destructive waves pick up beach material and hurl them at the base of the cliff. Over time this can loosen cliff material, forming a wave cut notch

Abrasion: occurs as breaking waves, concentrated between the high and low watermarks, which contain sand and larger fragments wear away the base of a cliff or headland. It is commonly known as the sandpaper effect. This process is particularly common in high energy storm conditions

Hydraulic action: waves hitting the base of a cliff causes air to be compressed in cracks, joints and folds in bedding planes, causing repeated changes in air pressure. As air rushes out of the cliff when the wave retreats it leads to an explosive effect as pressure is released. This process is supported further by the weakening effect of weathering. The material breaks off cliffs, sometimes in huge chunks.

Attrition: when waves cause rocks and pebbles to bump into each other and break up

What factors affect the rate of coastal erosion?

fetch of waves

wind strength

an area of coastline with no protection

geology of the cliff

Coastal transportation

Solution: dissolved chemicals often derived from limestone or chalk

Suspension: particles carried within the water

Saltation: a 'hopping' or 'bouncing' motion of particles too heavy to be suspended

Traction: large pebbles rolled along the seabed

Longshore drift

Longshore drift is the zig-zag movement of material along the coast by sea

It happens when waves approach the beach at an angle

The swash carries material up and along the beach

The backwash carries material back down the beach at right angles

It contributes towards the formation of a range of depositional landforms such as spits and bars

The prevailing wind pushes a wave up a beach, carrying material in the swash

The backwash drags this material back down the beach due to the force of gravity

Another wave picks up beach material and moves it up the beach again

The backwash drags this material back down the beach

This whole process keeps repeating, moving material along the coastline in the direction of the prevailing wind

Over time, this process can move significant amounts of sand and other materials from one area of coast to another, reshaping beaches and contributing to the formation of features like spits and bars

Coastal deposition

Coastal deposition involves materials transported by the sea being deposited

Takes place in areas where wave energy is lost ( sheltered bays)

Deposition forms beaches and sand dunes

As waves enter the bay they are funneled towards the beach, losing energy. Here sediment can no longer be carried or moved and therefore..

Material is deposited

As the wave goes through the bay it 'refracts' round the corner

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COASTAL EROSION LANDFORMS

What is a landform?

A feature of the landscape that has been formed or sculpted by processes of erosion, transportation or deposition

The role of geological structure and rock type

some rocks are tougher and more resistant than others

rocks such as granite and chalk form impressive cliffs and headlands because they are more resistant to erosion

softer rocks, clays and sands are more easily eroded to form bays or low lying stretches of coastline

geological structures includes the way that layers of rocks are folded or tilted. Faults are cracks in rocks. These are lines of weakness that can be easily eroded

Headlands and bays

A headland is an area of resistant rock that extends from the coastline into the sea

Headlands are formed from hard rock that is more resistant to erosion such as chalk, limestone and granite

Headlands form along discordant coastlines where bands of soft and hard rock outcrop at a right angle to the coastline

Due to the different nature of rock, erosion occurs at different rates

Less resistant rock erodes (boulder clay) more rapidly than more resistant rock

The bands of soft rock, such as sand and clay, erode more quickly than those of more resistant rock such as chalk

This leaves a section of land jutting out into the sea called a headland.

A bay is an inlet of the sea where the land curves inwards

The areas where the soft rock has eroded away, next to the headland, are called bays

Sandy beaches are often found in the sheltered bays where waves lose energy, and their capacity to transport material decreases, resulting in material being deposited

Where the geology alternates between strata of soft and hard rock, it is called a discordant coastline.

A concordant coastline is where the same rock runs along the length of the coast and they tend to have fewer bays and headlands

Dorset

Along the coastline of Dorset, there are concordant and discordant coastlines

The concordant coastline runs from west to east along the south coast

The discordant coastline runs from Studland Bay to Durlston Head as the geology changes from clay and sand, to chalk, to clay and sands again, to limestone

Cliffs and wave cut platforms

Cliffs are shaped through erosion and weathering

Soft rock erodes quickly, forming gentle sloping cliffs

Hard rock forms steep cliffs

Where cliffs are made of more resistant rock, wave-cut platforms are often formed

A wave-cut platform is a wide, gently sloping surface found at the cliff's base and extends into the sea

The sea attacks a weakness in the base of the cliff, for example this could be a fault in chalk

A wave-cut notch is created by erosional processes such as hydraulic action and abrasion

As the notch becomes larger, the cliff becomes unstable and collapses as a result of gravity

The cliff retreats inland

The material from the collapsed cliff face is eroded and transported away, this leaves a wave-cut platform

The process repeats over time

Caves, arches and stacks

Lines of weakness in a headland, such as faults, are particularly vulnerable to erosion

The energy of the waves wears away the rock along a line of weakness to form a cave

Over time, erosion may lead to back-to-back caves breaking through a headland to form an arch

Gradually the arch in enlarged by erosion at the base and by weathering processes, such as freeze-thaw, acting on the roof

Eventually the roof will be worn away and collapse to form an isolated pillar of rock known as a stack

The stack is eroded and collapses, forming a stump (Old Harry in Dorset)

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COASTAL DEPOSITION LANDFORMS

Deposition happens when swash is stronger than backwash and is associated with constructive waves

A landform is created by material deposited by the sea

Beaches

Beaches are deposits of sand and shingle at the coast

Sandy beaches are mainly found in sheltered bays

The waves entering the bay are constructive with strong swash and weak backwash

Spit

A spit is an extended stretch of beach material that sticks out to sea and is joined to the mainland on one end

Longshore drift moves material along a coastline

Where the coastline changes direction, or the power of the waves is reduced, material being transported is deposited

The deposited sediment builds up over the years to form a long ridge of material called a spit

A spit is an unstable landform; it will continue to grow until the water is too deep or until material is removed faster than it is deposited

Strong winds or tidal currents can cause the end of the spit to become curved to form a feature called a recurved end

In the sheltered water behind the spit, deposits of mud has built up, this forms a saltmarsh.

Spits typically form in areas where the coastline has a sudden change in direction, such as at river mouths or sheltered bays

Sediment is transported along in a zig-zag motion

Bars

A bar is a ridge of sand or shingle that joins two headlands on either side of a bay

Longshore drift may cause a spit to grow right across a bay, trapping a freshwater lagoon behind it

An offshore bar is formed where the sea is shallow, where the seabed gently slopes

Visible off shore bars, parallel to the coast, are known as barrier islands

Sand dunes

Sand dunes are small hills of sand found at the top of a beach, above the reach of waves

Onshore winds cause the formation of sand dunes at the back of the beach

Sand is deposited by wind around an object such as a rock, forming embryo dunes

Over time, vegetation such as marram grass stabilize the sand dunes forming foredunes and tall yellow dunes and then grey dunes

As the vegetation around the foredunes decomposes, nutrients are released and soil starts to form

A wider range of plants are then able to colonize the dunes

Winds can form depressions in the sand called dune slacks, in which ponds may form

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COASTAL LANDFORMS AT SWANAGE

Swanage is a seaside town on the south coast of England

It is located in a sheltered bay and has a broad sandy beach

Has lots of depositional landforms

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MANAGING COASTS-HARD ENGINEERING

Hard engineering coastal management techniques are typically used to protect settlements

They are used to deflect the power of waves

They are expensive to install and maintain

It involves building artificial structures that control natural processes

Last only a short time

Visibly unattractive and unsustainable

They often increase erosion in other places further down the coast

Groynes

wooden barriers constructed at right angles to the beach to maintain material

This material is trapped between groynes and cannot be transported away by longshore drift

Groynes help encourage a wide beach that helps absorb energy from waves, reducing the rate of erosion

ADVANTAGES:

Social: Groynes do not affect acess to the beach, create a wider beach which attracts tourists

Economic: They are relatively cheaper than other structures (£150000 each at every 200m), they are cheaper to repair than other structures, attracting tourists boots the local economy

DISADVANTAGES:

Social: Groynes act as a barrier which impedes people walking along the beach

Environmental: By interrupting longshore drift they starve beaches further along the coast often leading to increased rates of erosion elsewhere ultimately shifting the problem and not solving it

Economic: The increases erosion elsewhere leads to having to buy more defences, groynes need regular maintenance, they are ineffective during storm conditions

Sea walls

Usually built along the front of cliffs or settlements or other areas of valuable land

They are recurved, which means that the waves are reflected back on themselves

Typically made of concrete

ADVANTAGES:

Social: Gives people a sense of safety and security, often have promenades for people to walk on

Economic: Sea walls have a long lifespan and are effective defence against the sea

Environmental: Sea walls do not impede the movement of sediment along the coast by longshore drift

DISADVANTAGES:

Economic: Very expensive (£5000-10000 per m) and high maintenance costs

Social: Sea walls can affect access to the beach, Coastal flooding can occur when waves overtop the sea wall

Environmental: Unattractive, destroy habitats, Can increase erosion at the base of the sea wall which affects the coastal system

Rock armour

Rock armour is a barrier of large boulders placed before a cliff or sea wall to absorb energy and reduce backwash by encouraging percolation

ADVANTAGES:

Social: It does not impede access along the beach, used for fishing

Economic: Relatively cheap and easy to maintain (£ 200000 per 100m), can last years if well maintained, quick and easy to construct

Environmental: Does not impede sediment movement along the coast by longshore drift

DISADVANTAGES:

Social: Access to the beach is limited

Economic: Costs increase when the rocks are imported as they often come from abroad

Environmental: Unattractive, often do not fit in with local geology

Gabions

Wire mesh cages filled with rocks or pebbles

They are placed at the back of sandy beaches

As water enters the cage, wave energy is absorbed and dissipated

ADVANTAGES:

Social: it does not impede access to the beach

Economic: relatively cheap (£ 50000 per 100m), quick to build and cheaper to maintain

Environmental: can improve drainage of cliffs, can eventually become vegetated and merge into the landscape, do not impede sediment movement

DISADVANTAGES:

Social: In damaged state gabions are dangerous, access to beach may be difficult

Economic: Can only be used on sandy beaches as material thrown on them from pebble beaches would degrade them

Environmental: damaged gabions are unsightly and dangerous to seabirds

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MANAGING COASTS-SOFT ENGINEERING

A sustainable, long term coastal management solution

Does not involve building artificial structures

less expensive

sustainable as they work with natural processes

Beach nourishment

Beaches are made higher and wider by importing sand and shingle to an area affected by longshore drift to increase its height and width to provide protection from erosion or flooding by absorbing wave energy

ADVANTAGES:

cheap and retains natural appearance of the beach

beaches are a natural defence against erosion

beaches attract tourists, bringing economic boosts to the area

DISADVANTAGES:

Large storms will require further beach replenishment

Expensive (£500000 per 100m)

People may be temporarily prevented from using the beach for several days during maintenance

Managed retreat

when areas of the coast are allowed to erode

It is a deliberate policy of allowing the sea to flood or erode an area of relatively low-value land

ADVANTAGES:

retains the natural balance of the coastal system

eroded material encourages the development of beaches and salt marshes

creates new habitats and encourages more wildlife to live in the area

DISADVANTAGES:

farmers can lose their land

Dune regeneration

Sand dunes are effective buffers to the sea but are easily destroyed and damaged by trampling

Marram grass can be planted to stabilize dune and to help them develop

It involves taking action to build up dunes and increase vegetation

New sand dunes can be created to protect from coastal flooding

ADVANTAGES:

provides a barrier between the land and sea

cheap (£200-2000 per 100m)

maintains a natural looking coastline

can increase biodiversity by providing a greater range of habitats

DISADVANTAGES:

time consuming

can be damaged by storms

temporary fencing may cause people to not respond well

Dune fencing

Fences are constructed on a sandy beach along the seaward face of existing dunes to encourage new dune formation

These new dunes help to protect the existing dunes

ADVANTAGES:

cheap (£400-2000 per 100m)

minimal impact on natural ecosystems

control public access to protect other ecosystems

DISADVANTAGES:

can be unattractive if fences break

people may not respond well to being fenced off from certain areas

regular maintenance needed, especially after storms

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Questions

What are the advantages and disadvantages of using hard engineering like sea walls and groynes to manage coastal erosion?

Hard engineering involves building artificial structures to protect coastal settlements and valuable land. Strategies like sea walls and groynes have several advantages. Sea walls are highly effective at preventing coastal erosion and flooding by absorbing wave energy, while groynes trap sediment, helping to maintain beaches that act as natural barriers against waves. However, these strategies have significant disadvantages. They are expensive to install and maintain, making them unsustainable in the long term. Additionally, groynes can disrupt natural sediment movement, causing increased erosion further down the coast, while sea walls can lead to scouring at their base due to reflected wave energy

What are the differences between hard engineering and soft engineering strategies for managing coasts?

Hard engineering involves building artificial structures, such as sea walls, gabions, groynes and rock armour, to protect the coast from erosion and flooding. These strategies are effective but very expensive to install and maintain. They often need to be replaced every few years, making them less sustainable in the long term. In contrast, soft engineering works with natural processes to manage coastal erosion and flooding. Examples include beach nourishment, dune regeneration, dune fencing and managed retreat. Soft engineering is much less expensive than hard engineering and is considered more sustainable because it has a lower environmental impact and works harmoniously with the natural environment. However, it may not provide immediate or strong protection in areas with severe erosion or high wave energy

What are the conditions required for the formation of coastal depositional features like spits and bars?

In order for depositional coastal features to form, several conditions are required. First, low-energy waves or constructive waves are essential because they have a strong swash and a weak backwash. This allows sediment to be deposited rather than removed from the beach. Second, a change in the coastline, such as a bend or sheltered area, can cause waves to lose energy and deposit sediment. Additionally, the zig-zag motion of longshore drift transports material along the coast until it is deposited in areas where wave energy decreases. Other factors that contribute to deposition include a plentiful supply of sediment from rivers or eroded cliffs, a gently sloping seabed that encourages deposition, and calm weather conditions that reduce wave energy. Together, these conditions lead to the formation of depositional landforms such as beaches, spits and bars.

What is managed retreat and what are its advantages and disadvantages as a coastal management strategy?

Managed retreat is the deliberate policy of allowing the sea to flood low-value land to reduce pressure on more valuable areas such as coastal settlements or tourist attractions. One advantage is that it benefits the environment by creating new habitats such as salt marshes, which increase biodiversity and act as natural buffers against storm surging and flooding. It is also cost effective and sustainable in the long term, as it reduces the need for expensive hard engineering structures. However, there are disadvantages to consider. Much of the low-value land is often farmland, meaning farmers lose their livelihoods and require fair compensation. Additionally, managed retreat can cause social disruption, as communities may need to relocate, which can be emotionally challenging and unpopular

What factors influence the rate of coastal erosion?

The rate of coastal erosion is influenced by several factors. one key factor is wave energy; destructive waves erode the coast due to their strong backwash and ability to remove sediment. The type of rock also plays a significant role-hard rocks such as granite are resistant to erosion, while soft rocks like clay erode more quickly. Weather conditions, such as storms, increase wave energy and accelerate erosion. Human activities, such as dredging or building coastal defences can alter natural processes and affect erosion rates. The tidal range influences how often the coastline is exposed to wave action, while vegetation helps stabilize cliffs and reduce erosion. Together, these factors determine how quickly a coastline erodes