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 swash

4. 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

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

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 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

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

seen at low tide.

2. Headlands and Bays (Discordant)

3. Headlands and Bays (Concordant)

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. Beaches

Constructive waves help build beaches by depositing material when waves lose energy.

2. Spits

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.

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.

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 wall

Advance 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

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

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 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 = Eustatic

2. 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.

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

Salt Marshes

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.