COASTS

Marine processes2

What is the coast? It is a narrow zone between the land and

the sea that is constantly changing due the effects of the land, sea and air acting upon it.

You may recall the processes that create river landscapes are Erosion Transportation DepositionAnd similar process create marine landforms as

well.

Here they are at work3

Including the usual suspects there is Wave scouring - waves breaking at the base of the cliffs swirl around the base and result in the removal of loose rock

Wave Pounding - breaking down of the cliff face due to the sheer force of the wave which can exert upwards of 30 tonnes / m2 when crashing on the cliffs.-

These are both variations on hydraulic action

Waves and Tides Tide is a regular change in sea level due

to the gravitational pull of the moon and to some extent the sun

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Waves are caused by winds- The strength of the wind Duration of the wind Fetch- Distance travelled by the wind

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How is energy transferred to create waves?

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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.

There are two main types of waves:

7 A constructive wave is small in height has a gentle angle has less energy has a stronger swash than backwash (material is moved up the

beach by the strong swash). So it is constructive because it is building the beach up – it is

constructing it

There are two main types of waves:

8 A destructive waves is large in height has a steep angle: the is a steeper gradient between the waves

because there is a shorter gap between the waves and each wave is high

has lots of energy has a weaker swash than backwash (beach is scoured and degraded

as the strong backwash pulls sand and shingle back down the beach) So it is destructive because it is removing material from the beach

– it is destroying it

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Transportation: Saltation, Traction, Suspension AND

Headlands and Bays (Discordant coastline)

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Concordant Coastline- alternating hard and soft rocks are parallel to the sea

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Formation of a cove e.g. Lulworth, Dorset

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e.g. Flanborough Head

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e.g. Spurn Head

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Salt marshes16

Sand Dunes17

This part maybe new? The role of sea level change in coastal features?

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An estuary Is larger than a river

mouth, for example the river Thames, and resulted from a river that flowed out into the sea from a valley with low hills on either side. When the ice melted further north, the sea level rose causing an entry to the sea considerably wider than its former mouth.

This is a submergent submergent coastlinecoastline - together with the next 2 slides

The affects of geology on coasts

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Summary: Hard rocks give high steep cliffs, with

bare rock on the rock face and boulders and rocks at the base

Softer rocks give gentler, less steep cliffs - the cliff face is smoother with evidence of slumping

The affects of vegetation on coasts20

Summary: The longer the coast line has been

established, the more likely vegetation is to be there - so not on a cliff face that is forever changing, but yes on sand dunes and mangrove swamps.

But be aware that only certain plants can withstand high salt content.

The major impact of vegetation is that once established, it reduces erosion

The affects of humans on coasts

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Summary: 1. Settlements: coastal lowlands are very

popular worldwide for settlement, especially protected bays and river mouth - they make good ports

2. Where economic development is possible along coasts, it will often happen - agriculture, industry, fishing, tourism and increasingly energy - wind turbines, wave and tidal power

3. Coastal management - man has sort to control the coastline over centuries - by reducing erosion with groynes, sea walls etc

Beach ecosystems - coralAre built up entirely of

tiny living creatures, each of which have their shells - these shells form reefs.

What do they need to survive?

Sea temperatures that never go below 180C but are best 23-250C

Light is needed for the corals to grow, so they are in sea less than 25 metres below the surface, but not be exposed to the air for too long if at all, as they dry out

They can only survive in sea water.

They need a lot of oxygen and so need strong wave action - lots of foamy white water.

They need clear clean water, so no sediments devoid of pollution.

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Why are corals under threat?

23 Primary impacts: Very pretty areas that attract tourists, reefs a great source of fish, farmers attracted by fertile coastal areas.

Secondary impacts: development of ports, blasting by fishermen, pollution from farming, sewage all damage pristine conditions needed by coral, deforestation leads to silting of coastal fringe

Tertiary impacts: coral declines, fish decline, tourists move on, local food supplies decline.

One more addition to the pot of trouble - global warming leads to a rise in sea temperatures making it too warm for some coral and the sea is acidifying (more CO2 absorbed making carbonic acid) and this is damaging the delicate shells of the coral and another cause of reef bleaching and eventually death.

27% of coral reefs are highly threatened and another 31% under moderate threat.

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Beach ecosystems - mangrovesMost common in SE Asia -

most found within 30 degrees latitude of the equator.

They have 1 foot on the land and one in the sea.

The shore needs to be soft and muddy enough for them to take root. The shoreline needs to be undisturbed for them to do well.

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Why are mangroves a good thing?26

They are a fish nursery, they trap silt and help create new land, but possibly most importantly in times of rising sea level, they protect coastal areas in times of storm surges that accompany tropical storms, e.g. cyclones.

However they have been seen as disease-ridden and are therefore being cleared in many areas - what for? Nearly ½ are turned into fish farming areas, another ¼ for providing fuel and timber for construction.

Managing a retreating coast27

There are various strategies for defending the coastline. These can be divided into ‘hard engineering’ strategies (sea walls, groynes etc) and ‘soft-engineering’ strategies (beach replenishment, sand dunes etc).

SEA WALLS: These are massive concrete structures which may either be straight or

curved (a 'bull-nose sea wall’) Advantages: They provide strong protection to the land immediately

behind the wall. Disadvantages: Waves in storm conditions may break over them. They

are expensive to build and maintain. GROYNES These are wooden or rock structures (in which case they are called

boulder groynes) which run along the beach at right angles to the sea. They catch sediment that is being carried along the beach by longshore drift and prevent the removal of beach sediment downstream.

Advantages: They maintain the beach and may therefore prevent coastal erosion of the land behind the beach.

Disadvantages: They may catch so much longshore sediment that beaches downstream are deprived of sediment. They are unattractive to look at and so may put tourists off visiting a beach

Managing a retreating coast28

RIP-RAP (or ROCK ARMOUR) This consists of boulders placed in front of a cliff or building to

protect it. Advantages: It is less expensive to build and maintain than sea

walls. It is less unsightly than sea walls. Disadvantages: It is a less formidable barrier than sea walls. SOFT ENGINEERING RESPONSES SAND DUNES Sand dunes can be an effective form of defence against storm

waves. They are a very popular destination for tourists and the dunes are easily eroded by people walking and riding bikes on them. It is important, therefore, that they are 'stabilised'. This means that there are schemes to plant grasses such as Marram Grass, which prevent the sand from being blown away and that areas are fenced off to protect them.

BEACH REPLENISHMENT. This is carried on numerous beaches, the beaches at Weymouth and

Lyme Regis being but two examples. It has the benefit that it may look natural, especially if the sediment is local but, on the other hand, replenished beaches require constant maintenance and so this may be an expensive solution.

Managing a retreating coast29 MANAGED RETREAT The final response is to do nothing. The costs of

resisting the sea are sometimes questionable, especially if the defenses are only protecting farmland as is the case with long stretches of the Holderness coastline. This is, however, a controversial response and is, understandably often resisted by farmers.

Conclusion: Possible coastal defence measures cannot be looked merely on the basis of whether they are suitable for the place in question. The bigger picture must be considered. Not only may defences such as groynes have knock-on effects on places downstream but coastal defence is just one of a number of issues such as tourism, waste disposal, economic development and pollution that local authorities have to take account of.

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http://cdn.qldscienceteachers.com/junior-science/astronomy/tides.jpg http://www.rsmas.miami.edu/blog/wp-content/uploads/2012/10/

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