Coastal

Coastal

Parn Yr.11

Coastline

•The coastline marks the meeting point between the land and sea.

•This area is dynamic and constantly changing in nature due to the processes of

erosionerosion, transporttransport and depositiondeposition that take place.

•The extent of these processes are dependent on the amount of energy available.

•At the coastline the energy source is the wind which transfers its energy to the

water creating waves.

Wave

1. Wind creates friction on the waters surface; 2. Frictional drag between the wind and the waters surface causes water particles

to rotate and energy is transferred forward; 3. When the wave reaches shallow water, it slows down due to friction between

the base of the wave and the sea bed. The shape of the wave becomes increasingly elliptical;

4. The top of the wave continues to move forward as it is unaffected by the friction with the sea bed. It becomes steeper and steeper and eventually breaks;

5. Water moves up the beach as the swash; 6. Water then returns back down the beach as the backwash.

Types of wave

Constructive Wave Destructive Wavesmall in height large in height

gentle angle steep

less energy lots of energy

strong swash and weak backwash (material is moved up the beach by the strong swash)

weak swash and strong backwash (beach is scoured and degraded as the strong backwash pulls sand and shingle back down the beach)

Coastal ErosionAbrasionAbrasion (corrasion) - when the sea throws rock up to hit the cliff, and break.

Hydraulic PressureHydraulic Pressure - this is where erosion occurs due to the pressures exerted by breaking waves as air trapped in cracks in the cliff is compressed by the water. This compression and sudden release gradually forces the cracks apart.

SolutionSolution (corrosion) - this is where salt water can act to dissolve some chemicals in the rocks, for example in limestone, calcium carbonate is dissolved, weakening the rock.

AttritionAttrition - when the sea carries the rock to hit other rocks, making the rock break into small pieces.

Coastal Erosion Features :

Headlands and BaysHeadlands and Bays

Coastal Erosion Features :

Cliff ErosionCliff Erosion

Coastal Erosion Features :

Erosion of headlandErosion of headland

Coastal TransportWeathering and erosion at the coast produces large amounts of material

which is moved along the coast line and out to sea by the action of waves. Up and down the beach:

• Material is moved up the beach in the swash and back down the beach in the backwash.

•Constructive waves move large amounts of material up the beach as they have a strong swash, whereas destructive waves move large amounts of material down the beach due to their strong backwash.

Movement of material along the coastline: LONGSHORE DRIFT

The main movement of material at the coast is the movement of material along the coastline by the process of Longshore drift.

Amounts of Longshore Drift depend on:•The strength of the waves  •Size and amount of material available for the movement •Incline (slope) of the beach

There are four possible types of transport within the water:

Solution - material carried dissolved in the water.

Suspension - fine material carried suspended within the water itself

Saltation - material which is too heavy to be continuously held in suspension is bounced along the sea bed.

Traction - the heaviest material is simply rolled along the sea bed.

Types of transportation

Coastal Deposition FeaturesAlthough some material eroded at the coast is washed out to sea,

most of the material is transported along the coast by longshore drift.

Deposition will occur when the waves are now longer able to transport material due to a loss of energy. This is the case with constructive waves, where material is moved up the beach in the strong swash, but the weak backwash means material is deposited to build up the beach.

Deposition commonly occursDeposition commonly occurs:•where the water is sheltered (e.g. a bay) and the waves lack energy

•where the coast is shallow and the increased friction between the water and the sea bed reduces the energy available for transport. 

Coastal Deposition Features:Deposition of material results in the formation of a number of distinctive features: beaches; spits; bars and tombolos.

Coastal Deposition Features: BeachesBeaches

Beaches are the main features of coastal deposition. A beach is defined as the gently sloping area of land between the high and low water marks.

Coastal Deposition Features: SpitsSpits

What are Spits? Spits are long narrow ridges of  shingle and sand extending out into the sea or across a river estuary.

1. Longshore drift moves material along the coastline.

3.Over time, the spit grows and develops a hook if wind direction

changes further out.

4.Waves cannot get past a spit, which creates a sheltered area where silt is deposited and mud flats or salt marshes form.

2.A spit forms when the material is deposited.

Coastal Deposition Features: BarsBars

What are bars and how are they created?

A bar is formed where a spit continues to grow across a bay, creating a lagoon behind it. The lagoon, becomes an area of still water

and a salt marsh forms in this low energy zone. Over time the lagoon will become

infilled by deposition as either rivers flows in to it depositing material, or as waves break over the top of the Bar depositing coastal

material

Coastal Deposition Features: TomboloTombolo What are tombolo's and how are they created?

Tombolo's are ridges of sand and shingle which join the mainland to an island. Tombolo's are created through the process of longshore drift. Where there is a change in the shape of the land, a spit forms in the shallow / sheltered water. A tombolo is formed where the spit continues to grow until it reaches an island, forming a link with the mainland.

Coastal Management

Rapid coastal erosion often poses a threat to the settlement, industry and recreation that has grown up along the coast and we often look to protect the coast from erosion through appropriate management of the coastal system.

Method of Protection How does it work? Advantages Disadvantages

Concrete Wall, curved under the side to deflect the power of the waves.

Sea walls reflect rather than absorb wave energy

Most effective means of preventing erosion

Most expensive Deflected waves often scour

the base, undermining the wall (may eventually collapse)

Large boulders on the beach - lesson the force of the waves by absorbing the

wave energy within the gaps between

the rocks

Relatively Cheap Use natural

materials / rocks

Environmentally ugly Can be undermined and

removed by waves due to washing away of sand and shingle beneath.

Cages of boulders built into the cliff face - small rocks help to absorb the wave

energy

Effective where severe erosion and cheaper than sea walls

Environmentally ugly (usually used in large numbers)

Wooden structures break the force of the waves and trap beach material behind them

Much cheaper than a sea wall

Effective at breaking the force of the waves

Less durable than a sea wall - may need replacing quicker

Don't give total protection to base of cliff

Environmentally ugly

Method of Protection How does it work? Advantages Disadvantages

Wooden or in some cases steel structures

that stop longshore drift and build up / anchor the

beach, protecting the base of a cliff

Stops longshore drift encouraging the build up of the beach and effectively reducing erosion.

Can increase erosion further down coast by stopping longshore drift and starving areas further down coast of sediment.

Build up the beach by replenishing beach

material, particularly at the base of structures to

provide a 'natural' solution to absorbing

wave energy.

provides natural solution provides natural solution 

can be expensive to keep transporting large amount of sand - sediment moved by longshore drift so will need frequent replenishment unless used with other defences