Coastal System Revision

Page 1

Coasts as a natural system Part 1.

Controls.

System of a coast.

Definition of a coast: The coast is a narrow contact zone between the land and sea. It is constantly changing due to the effects of land, sea and air processes. It is an open system as it has inputs and outputs.

Weathering: The breakdown of rock at the Earth's surface to create sediment that remains in situ.

Erosion: The wearing away of the Earth's surface by mechanical action of glaciers, wind and sea.

Transportation: The movement of material by a glacier, wind, sea or river.

Deposition: Happens when the sea loses energy and drops material it's carrying. This leads to the formation of spits and bars.

Sub-aerial processes: Processes affecting the cliff face, such as weathering and mass movement.

System of a coast.

Inputs: Sediment can be introduced from sub-aerial processes on land, via rvers or offshore from the sea. Energy s introduced in the form of wnd, waves, tides and currents.

Processes: Mechanisms that help to move matertial between stores. These can be marine (erosion, transportation, deposition), terrestrial (weathering and mass movement), atmospheric (precipitation, storms, wind) and biological (growth of plants.)

Stores: eatures that are shaped by processes or that have sediment added to or removed. from. Examples include headlands, spits, caves, beaches, stacks and bays.

Outputs: Losses of energy and sediment to the system. For example, sediment can be taken out to sea and lost to the ocean.

Controls.

Climate: Precipitation leads to chemical weathering- carbonic acid. Chalk and Limestone contain calcium carbonate. Wind= greater erosion. Freeze thaw= temperature.

Geology: Boulder clay= soft rock= erode quicker= Bays. Chalk and Limestone are more resistant, and are found in Headlands.

Rock Structure: Cracks are lines of weakness in rocks and are attacked by waves and erosion. The layers of rock are known as Strata. Vertical cracks are known as Joints. Horizontal cracks are known as bedding planes and are lines of weakness.

Sea level rising: As sea levels rise, erosion occurs more frequently.

Flows.

Longshore Drift (LSD): The movement of sediment down the coast due to the direction of the prevailing wind.

Waves: The transfer of energy from the sea to the land, due to wind.

Mass movement: The movement of sediment from the cliff face to the cliff foot after being broken up by weathering or affected by gravity.

Erosion: The removal of sediment from the cliff foot and he use of this material to wear away the cliff further.

Energy.

This is provided by waves and currents in the sea. If this is high, it leads to erosion and transportation. If it is low, deposition occurs. A further example is gravity acting on cliffs.

Dynamic Equilibrium.

This is when there is a balance between inputs and outputs in a constantly changing system. If something in a system changes, for example increased deposition, the equilibrium is upset. Feedback mechanisms on the beach act to bring the coast back to dynamic equilibrium.

Feedback mechanisms.

Positive: Where a change is amplified. This may happen due to human interference with the system. For example, coastal management can lead to increased erosion along a coast

Negative: Where a change is dampened down. Natural systems work to regain dynamic equilibrium.

Depositional Landscapes.

Sediment is moved down the coast due to transportation via longshore drift, due to the direction of the prevailing wind.

When the coastline shape changes (for example at an estuary), deposition can begin as a result of a loss of energy, creating a spit.

Deposition of alluvium by the river builds up new land behind the spit. Plants colonise this land, creating a salt marsh.

Erosional Landscapes.

On a Discordant coastline, landforms develop on a headland with the sequence:

Crack, Cave, Arch, Stack, Stump (CraCASS).

This is an EROSIONAL landscape.

On a concordant coastline, when the sea breaks through the resistant rock, it will erode the softer rock behind more quickly, forming characteristic landforms (COVES)

On a discordant coastline, headlands are left sticking out into the sea, so feel te full force of the sea's erosional power. This forms characteristic landforms. (HEADLANDS AND BAYS)

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Tides and Currents.

Neap tides.

Less gravitational pull.

Smaller than average high/low tides.

Small tidal range.

10-30% lower than average.

Spring tides.

All in line.

Lower tide than usual.

Greater gravitational pull on water- higher tide than usual.

Moon and sun affect tides.

Moon is most significant- have more influence as it's closer.

2 spring tides and 2 neap tides per lunar month (29 days.)

Storm Surges.

Very high tide- caused by the storm.

The high wind velocity gives big waves.

In the North Sea, there are 3 factors, and these are: Low pressure systems (create a higher tide), Spring tides ( Sun moon and Earth aligned, giving larger tidal range; sun and moon work together ad give a greater gravitational pull) and Concentrated in a small sea area (funnels water towards the coast, and strong winds create big waves.)

High and Low Energy Coasts.

High energy coasts:

Erosion= Headlands/Bays.

Destructive Waves

Transportation.

Erosion>Deposition.

Long Fetch, e.g. Lulworth Cove (3000km+).

Low Energy Coasts:

Deposition= Spits/Bars/Tombolos/Salt Marsh

Constructive Waves

Short fetch, e.g. Chesil Beach.

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Energy on the Coast: Wind and Waves.

1. Sediment: From offshore, rivers, along the coast, and rocks from the cliff face.

2. Energy: From waves, tides, current and wind.

Coastal energy 1: Wind.

High wind speed= higher wave energy.

Prevailing wind controls direction waves approach and direction of transportation- most coasts have this.

Fetch is the distance of open water that the wind blows over. Large fetch distance= greater energy.

Wind is vital to wave formation- "frictional drag" of wind.

Wind crucial to erosion- pick up sediment- use it to erode features (abrasion).

Wind can transport sediment from coast and inland.

Wind processes= aeolian processes.

Coastal energy: Waves.

Wave energy depends on strength of wind, length of time it is blowing and the fetch. Frictional drag caused by the wind s it passes over the sea, causing waves to form.

Wave Height: Distance between the trough and the crest.

Wavelength: The distance between the crests.

Wave frequency: The number of waves that pass a given point in a set period of time.

The transfer of energy from the wind blowing over the sea surface.

The bottom of the wave touches the sand and slows down due to friction. The top becomes higher and steeper, until it topples over. A rush of water up the beach is known as the swash. The run of water back towards the sea is known as the backwash.

Wave Characteristics.

Constructive Waves:

Low height (less than 1m.)

Long length (up to 100m)

Gentle

Short fetch

6-8 waves per minute.

Spilling/Surging water movement.

Swash>backwash

Deposition is the dominant process.

Destructive Waves:

High height (1m+)

Short length (~20m)

Steep

Long fetch

10-14 waves per minute

Plunging water movement.

Swash<backwash

Erosion is the dominant process.

Wave Refraction.

Wave approaches irregular coastline.

High energy waves converge at headlands.

Depth of water increases at headlands and decreases towards bays and beaches.

Low energy waves diverge at beaches and bays.

Concentration of wave energy is greater at headlands, leading to its subsequent erosion.

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Sources of Sediment and Sediment Cells.

Sources of Sediment:

Rivers: Vast majority of coastal sediment. Especially in areas with high rainfall, as this results in more erosion. When it reaches the mouth, very small particles of sand, silt and clay get deposited in river mouths and estuaries. They are then reworked by waves and tidal currents.

Cliffs: This depends on the geology of the cliff. Soft rock results in erosion rates being as high as 10m per year, introducing a lot of sediment into the system. An example here is Boulder Clay in the Holderness Coast. Hard chalk cliffs, such as Flamborough Head, introduce less sediment into the system as less erosion takes place here.

Offshore: Sediment can be transferred into coastal zones by waves, tides and currents. Spring tides lead to stronger currents, especially in estuaries and channels (sea between mainland and island.) Storm surges can be caused by depressions and low pressure. Tsunamis are caused by earthquakes under the sea. Both can be responsible for the inputs of sediment.

Longshore Drift: This is the movement of sediment from one stretch of coastline to another. Overall movement of sediment along a coast, parallel to the shore.

Wind blown sand: Deposited in coastal regions. Sand dunes are semi-dynamic features that are accumulations of sediment from wind blowing sand onto the dune. Potential sources of sediment from wind blowing sand off the dune into the sea.

Glaciers: As glaciers slowly move across landscapes, they erode sediment from the land. When these ice shelves calve into the sea, sediment trapped within the ice becomes a source of sediment into the system.

Sediment Cells: England and Wales have 11 sediment cells. They can be divided into smaller sections to allow closer study and management. A stretch of coastline where the movement of sediment is more or less contained. Cells are usually bordered by 2 prominent headlands. Theoretically, they are a closed system. However, fine sediment can be found around headlands.

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Salt Marshes and Mudflats.

Stage 1: Mudflats aided by growth of Eelgrass- slows currents, increases deposition and only exposed at low tides.

Stage 2: Mud deepened. Halophytes colonise. Spartina has 2 root systems. Fine= bind mud. Deep= anchor Spartina in mud.

Stage 3: Develop close vegetation over mud= more colonising plants. Slows tidal currents. Humus. More mud/silt accumulation.

Stage 4: Creek systems develop. Hollows form= sea water trapped. Evaporates= salt pan being too salty for plants.

Stage 5: Rushes/Reeds become stabilised. Succession completed by growth of trees (oak). Land now rarely covered by the Sea.

River Estuaries:

Important sediment store.

Huge quantities of river sediment is deposited as the river velocity decreases as it meets the flow of the incoming tide.

The sediment at this stage of the river is primarily fine sediments, such as clays, sands and silts, due to erosion that has taken place along the river course.

Mudflats:

Only develop on sheltered shorelines that are not exposed to pwerful waves and where wave energy is low:

Sheltered areas where deposition occurs (e.g. landward side of a spit.)

River estuaries- where the fresh and saltwater meet.

Low lying areas of shore that are submerged at high tide and exposed at low tide.

Made of silt and clay.

Deposition occurs due to the opposing flows of the river and the sea, both of which are gentle, leading to further deposition.

Can cover extensive areas but are very vulnerable to change, such as sea level change.

E.g. Morecambe Bay where 4 river estuaries meet.

Flocculation: Fine clay and silt particles are carried in suspension in the sea and rivers. They are very rarely deposited due to their very small size- it takes very little energy to transport them. This causes clay to be deposited and accumulate that happens when salt water and fresh water meet. This causes individual clay particles to aggregate to form larger, heavier particles that enables them to sink and be deposited on the seabed.

Salt Marshes:

Develop from mudflats over time.

Often covered at high tide and exposed at low tide.

Develop over time like sand dunes, exhibiting a clear vegetation succession- a halosere.

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Sea Level Change- Associated Landforms.

Emergent Landforms.

1. Raised beaches and marine platforms are found above the high tide mark and are no longer exposed to marine processes.

2. Over time, the sediment on the raised beach becomes vegetated and the sand develops into soil.

3. Most parts of a marine platform are often hidden beneath fresh sediment deposits and distinguishing between the two is often challenging.

4. A marine platform is similar to a raised beach, however one clear distinction is that these have a very gentle gradient and often extend further inland.

5. Behind the beach, cliffs, caves, arches etc, are often found which are now only exposed to sub-aerial processes.

6. These landforms are slowly covered by vegetation and are known as Relict cliffs.

Submergent Landforms.

Rias: Drowned River Valleys.

Flooded areas close to the sea= large estuaries.

Interlocking spurs- stick out into rivers.

Floodplain will vanish beneath the rising water. Valleys at previous sea level have now submerged.

Plan: Shallower further inland. Wide and deep at mouth. Very large estuary at the mouth of a relatively insignificant river.

Cross-Section: Gentle/Shallower further inland.

Long section: Gentle.

EXAMPLE: Kingsbury Estuary, Devon.

Fjords: Drowned GLACIAL Valleys.

U shaped Valley. Fairly straight and narrow.

Plan: Known as a threshold.

Cross section: Maintains depth for a significant distance inland. Depth of over 1000m. Steep valley sides. Typically U shaped.

Long section: Shallower near the mouth. Glacier ice was thinner nearer the sea= less erosion. Known as a threshold.

EXAMPLE: Sogne Fjord, Norway.

Dalmatian Coasts: Series of offshore islands running PARALLEL to the Coast.

Form in landscapes where ridges and valleys run parallel to the Coast- not at right angles like Fjords and Rias.

Sea levels rise, valleys flood, although the tops of the ridges remain exposed.

EXAMPLE: Croatian Dalmatian Coast.

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Sand Dunes.

Accumulations of sand that has been blown off the beach by onshore winds, and shaped into mounds.

Sand is moved by saltation.

When there is a large tidal range, large amounts of sand is exposed at low tide and dries out.

Wind from the sea blows sand from the intertidal zone and a dune begins to form.

Sand towards the back of the beach becomes trapped by debris.

Sand accumulates on the leeward side.

The sand here has a high pH and lacks moisture, so only the most resilient plants can colonise, such as sea rocket.

These are known as pioneer species.

Embryo Dunes.

These are the first to develop.

These can be colonised by grasses such as couch grass and sea rocket.

The dunes grow upwards by accumulating wind-blown sand which helps to stabilise the surface.

Their height interrupts saltation.

These are robust species which are drought resistant (Xenophytes) due to the lack of water, and salt resistant (halophytes.)

They spread vigorously underground shoots known as rhizomes.

These are horizontal roots that have reproductive shoots attached to them.

Plants need certain features to survive this environment:

Saltwort has succulent leaves to store water.

Sea couch is prickly with thorn-like leaves to reduce transpiration and conserve water.

All of these plants add organic matter humus to the dunes which aids water retention and lowers the pH.

Foredunes.

Upward growth of dunes raises the height (up to 20m) meaning that these are beyond the reach of the highest high tides.

These are known as foredunes and are much bigger in size than embryo dunes.

Their colour is initially yellow, but as organic matter is added to the sand through dying and decaying plants, the humus darkens the sand to a grey colour.

The pH is also lowered through the additional humus in the soil.

Marram grass features heavily here and has deep roots to reach the water table.

Fixed Dunes.

As the moisture and humus content increases and the pH decreases within the sand, more plants are able to colonise and the dunes become fixed and turn a grey colour.

These plants could not have tolerated the early dune conditions and they include:

1) Lichens, mosses and flowering plants.

2) e.g. Creeping fescue, creeping willow, dewberry and heather.

Dune slacks.

These are depressions between dune ridges.

These are damper areas where the water table is closest to the surface.

Mosses, reeds, rushes and willows should be able to grow here, however that is dependent on local moisture content.

Dune Heath and wasting dunes.

As distance from the sea increases, the supply of beach sand decreases and is eventually cut off.

This produces much smaller dune features.

Plants such as heather, gorse and buckthorn thrive here due to the more acidic soil, with higher humus and water retentiveness.

Blowouts.

These can occur in any position along the dunes. Where wind is funnelled through areas and removes sand, blowouts are found.

If they are not stabilised by plants, significant volumes of sand can be lost.

Sand dune succession.

Sand dunes are an example of succession- a plant community whose structure develops over time.

Succession that develops over time is called a psammosere.

At each stage, plants alter the particular conditions present thus allowing for other plants to colonise.

As each new species takes hold, the process is repeated.

In time, the rear of the dune may be colonised by beech and oak trees- this is the climatic climax vegetation type for the British Isles.

If the succession is not allowed to reach its natural end point (in this case, an oak forest) and reaches a sub-stage.

This is called a plagioclimax.

Interferences of sand dune succession include: grazing sheep/cattle, planting of different trees, or other human interference.

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Sub-aerial processes: Weathering.

Weathering is the breakdown of rock in situ (original place) at, or close to, the ground.

Frost Shattering: Occurs when water enters a crack in rock when it rains and freezes in cold weather. When water freezes, it expands by 10%.

Salt crystallisation: When salt water evaporates, it leaves salt crystals behind. Grow over time and exert stresses in the rock, causing it to break up. Salt can also corrode rock, particularly if it contains traces of iron.

Wetting and drying: Frequent cycles of wetting and drying are common on the coast. Rocks rich in clay expand when they get wet and contract as they dry. This can cause them to crack and break up.

Carbonation: Rain absorbs Carbon Dioxide from air to form a weak carbonic acid. Reacts with Calcium Carbonate in rocks, such as limestone and rock. Cooler rain means more Carbon Dioxide is absorbed.

Oxidation: The reaction of rock minerals with Oxygen (e.g. Iron) to form a rusty red powder leaving rocks more vulnerable to weathering.

Plants: Thin plant roots grow into small cracks in a cliff face. These cracks widen as the roots grow which breaks up the rock.

Decaying plants: Water running through decaying vegetation becomes acidic, which leads to increased, chemical weathering.

Animals: Birds (e.g. Puffins) and animals (e.g. Rabbits) dig burrows into cliffs.

Marine Organisms: Marine organisms are also capable of burrowing into rocks r of secreting acids (e.g. Piddocks and Limpets).

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Sub-aerial processes: Mass Movement.

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

Mudflow: Earth and mud flowing downhill, usually over weak bedrock (clay) after heavy rainfall. Water gets trapped within rock, increasing pore water pressure which forces rock particles apart and leads to slope failure. Heavy rainfall leads to increased pore pressure, which forces the rock particles to break apart, which leads to slope failure.

Runoff: When overland flow occurs down a slope or cliff face, small particles are moved downslope to enter the littoral zone, potentially forming an input into the sediment cell.

Rockfall: Involves the sudden collapse or breaking away of individual rock fragments (or a block of rock) at a cliff face. This is triggered by mechanical weathering or an Earthquake.

Soil creep: An extremely slow form of movement individual soil particles downhill. A zigzag movement that is similar to LSD. This involves particles rising towards ground surface due to wetting or freezing and then returning vertically to the surface in response to gravity.

Solifluction: Similar to soil creep but specific to cold periglacial environments. In the summer, the surface layer of soil thaws out an becomes extremely saturated because it lies on top of impermeable frozen ground. The active layer within its blanket of vegetation slowly moves downhill y a combination of heave and flow. Forms features called solifluction lobes.

Landslides: Block of rock moving very rapidly downhill along a planar surface, often a bedding plane that is roughly parallel to the ground surface. They are frequently triggered by earthquakes or very heavy rainfall, when the slip surface becomes lubricated and friction is reduced. They tend to be rapid and pose a considerable threat to people and property.

Land slip rotational slump: The slide surface is curved, rather than flat. Occurs in weak and unconsolidated clays and sands. Permeable rocks overlie impermeable rocks, which causes a build up of pore water pressure. Characterised by a sharp break of slope and the formation of a scar. Multiple landslips can result in a terraced appearance on the cliff face.

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Landforms and Landscapes of Coastal Deposition: Beaches.

Sand: Produces beaches with a gentle gradient (wide and flat). Ripples are developed by wave action or tidal currents. Small particle size means the sand becomes compact when wet. This allows for little percolation in the backwash.

Ridges and Runnels: These form in the sand at the low-water mark on shallow beaches. They run parallel to the shoreline and are broken by channels that drain the water off the beach. They are intervening depressions in the sand and are formed as the wave energy is spread across the beach.

Cusps: These are semi-circular depressions. They form where waves break directly onto the beach. They form on beaches with mixed sand and shingle. The sides of cusps channel the incoming swash into the centre. This movement creates a stronger backwash that removes the material down the beach. The coarser material is deposited on the horns of the cusps, further developing their semi-circular shape.

Berms: These are a series of ridges formed in the sand and shingle. They are 1-2 metres high. These mark the successive high tides, as the tides move from neap to spring. They are built up by constructive waves with little energy so material is deposited.

Shingle: Shingle may make up the whole or upper part of the Beach. The larger the material, the steeper the gradient.This is because water percolates through shingle so backwash is limited, so little material is removed.

Storm beach: A ridge composed of the biggest boulders thrown by the largest waves. Created by strong swash at high spring tides. They remain unmoved because subsequent tides cannot reach them.

Beach: Depositional landform that extends from the highest tide mark to the lowest tide mark. They are a temporary store in the coastal system.

Beach accretion: Growth or increase by the gradual accumulation of additional layers of sand. This occurs during a prolonged period of constructive waves.

Swash-aligned beach: Form in low energy environments, such as bays. Waves break parallel to the shore. The sediment is moved up and down the beach. Lateral= sideways. Little lateral movement.

Drift-aligned beach: Form when waves approach the beach at an angle. LSD moves sediment along the beach and often creates a spit. Sediment is often graded along the beach finer. Carried further and increasingly rounded as they move.

A spit is a long, narrow piece of sand or shingle that has one end attached to the mainland and the other projecting into the sea o covering part of an estuary. E.g. Spurn Head, Holderness Coast.

The formation of a spit:

Sediment is carried along the coast via LSD, following the direction of the prevailing wind.

When the coastline changes direction at a headland, material is deposited in water sheltered by the headland, due to a decrease in energy.

Deposition continues at the headland to build up slowly to sea level.

Continued LSD and deposition causes the spit to extend in length.

Growth of the spit is normally limited by an estuary as the river current carries deposited sediment out to sea.

Salt marshes develop in the sheltered water behind the spit where wave action is limited. This allows sediment to collect and vegetation grows.

Occasionally, the wind direction can alter, causing the sediment to be pushed inland which creates a curved end This is called a recurved tip.

The spit continues to extend in the prevailing wind direction which extends the spit further past the curve.

Sometimes the recurved tip can act as a new "headland" and change the direction of a spit. Where they join is called a compound spit.

Bar: A spit grows across a bay joining 2 headlands. Sediment brought to bar by LSD in direction o prevailing wind. Change in coastline direction, however no estuaries are present to break the spit formation. As sediment accumulates a extends, it may attach to a subsequent headland. This creates a lagoon behind it.

Barrier Island: When a barrier beach becomes separated from the mainland. They can be flat or contain sand dunes. Sea level rise. Chains of several islands. Absorb energy and protect coastlines.

Tombolo: A spit grown out from the mainland to join an island. Sediment brought by LSD in direction of prevailing wind. Change in the shape of a headland. It is 30km long.

Offshore Bar: A mound of sand found a short way off the coast, out to sea. Submerged under the sea. Destructive waves plunge out to the beach. Weak swash and strong backwash pulls material off the beach, leaving a concave beach. Eroded material deposited offshore. Store of sediment (temporary).

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Shoreline Management Plans.

Three distinctive coastal units:

Flamborough Head: Chalk landscape with landforms formed through coastal erosion.

Bridlington Bay to Spurn Head: Extensive zone of erosion and sediment transfer, characterised by very rapid cliff retreat.

Spurn Head: Spit at the estuary of the River Humber.

Management along the Holderness Coastline:

Bridlington: Location- Lots of tourists related businesses- 2200 jobs and annual income of £34million. Fishing port-multi-million pound shellfish export. Habitat for sea birds. Management- Destructive waves sheltered by Flamborough Head and artificially by a 4.7km long concreted promenade and sea wall (worth £25.8 million).

Hornsea: Location- 400 jobs and an income of £8million per year. Caravan parks, campsites and other tourist related retail facilities. Management- 1.86km of sea wall (worth £11.1million). Sections of groynes and rock armour (£6.25million).

Mappleton: Location- population of 300. B1242 runs through the village to Bridlington (North) and Withernsea (South). Some sections are less than 50m from the coast. Management- n 1991, £2mllion was spent on building rock armour and rock groynes. It is cheaper than re-routing the B1242 further in land.

Withernsea: Location- 500 jobs and an annual income of £9million per year. Similar to Hornsea. Management- 1.21km of sea wall worth £7.3million. 0.9km of Rock Armour worth £2.7million. 2 metres of timber groynes.

Easington: British Gas and BP own the Gas Terminal. It accounts for 25% of Britain's gas supply. Previously eroded 1.8 metres per year (only 30 metres away at one point.) Management- 1km of rock armour worth £6.8million. Reassessed or cost-benefit analysis in 2020. Gas non-renewable.

Spurn Head: Temporary sediment store/sink. Made from materials eroded and transported via LSD. Narrow/frequently breached and destroyed by storms. Number of cycles of growth and decline the last approximately 250 years. It is 6km long and becomes an island at high tide. Management- In 1849, Groynes and revetments were built to stabilise the spit. These were maintained until 1960, when the spit was purchased by the National Trust. In 2013, tidal surges destroyed buildings and roads.

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Coastal Management.

Definitions.

Coastal Management: Human intervention in coastal landscapes with 2 main aims: Provide defence against and mitigate the impacts of flooding; provide protection against and mitigate the impacts of flooding.

Hard engineering: More traditional approach that works against natural processes. This involves the erection of structures and were very common up to the 1990s.

Soft engineering: More modern approach that works with natural processes. This involves allowing natural processes to occur rather than halting them.

Importance of Coastal Management:

About half of the world's population live within 60km f a coast and 75% of all large cities are at the Coast.

Coastal areas are under immense pressure for development, resulting in environmental damage and habitat destruction and pollution of coastal waters.

Risk of flooding and coastal erosion will increases global temperatures increase and sea levels rise.

Cost-benefit analysis:

Carried out before a management project is given the go-ahead. Costs are forecasted:

E.g. Sea wall- design, building costs, maintenance, etc.

Compare with the expected benefits, e.g. value of the land saved, housing protected savings in relocation of people, etc.

Costs and benefits- the 2 types:

Tangible- where costs and benefits are known and can be given a monetary value.

Intangible- Where costs may be difficult to assess but are important.

Projects where costs exceed benefits is unlikely to be given permission to go ahead.

Hard engineering:

Sea Wall:

Description: Stone/Concrete Walls. At foot of cliff/top of beach. Usually have a curved face.

Benefits: Effective prevention of erosion. Often have a promenade for people to walk along.

Disadvantages and Costs: Reflect wave energy. Intrusive and unnatural. Very expensive to build and maintain. £6000 per metre.

Rock armour:

Description: Large rocks placed at the foot of a cliff/top of the beach. Forms a permeable barrier to the sea- breaks up waves- allow some water to pass through.

Benefits: Relatively cheap and easy to construct and maintain. Often used for recreation.

Disadvantages and Costs: Intrusive. Look out of place with local geology. Dangerous for people clambering them. £100000 to £300000 per 100m.

Gabions:

Description: Small rocks that are encased in a mesh cage.

Benefits: Very cheap to make. Use local beach material. Stop erosion. Allows drainage.

Disadvantages and Costs: Not aesthetically pleasing. Quite easily broken. A lot of maintenance- costs a lot. Short lifespan. £30 per metre.

Revetments:

Sloping wooden. Concrete or rock. Structures placed at the foot of the cliff, or the top of a beach. They break up the waves' energy.

Benefits: Relatively inexpensive to build.

Disadvantages and Costs: Intrusive/unnatural. Need high levels of maintenance. Up to £4500 per minute.

Groynes:

Description: Timber or rock structures built at right angles to the coast. Trap sediment being moved along e coast by LSD.

Benefits: Work with natural processes to build up the beach, which increases tourist potential and protects the land behind it.

Disadvantages and Costs: Starve beaches. Lead to increased erosion elsewhere. Unnatural and can be unattractive. £5000-£10000 each (200 metre intervals.)

Offshore Reef/Breakwater:

Description: A partly submerged rock barrier, designed to break up the waves, before they reach the coast.

Benefits: An effective permeable barrier.

Disadvantages and Costs: Visually unappealing/potential navigation hazard. Similar cost to rock armour- depending on materials used.

Sustainable integrated approaches:

Sustainability means meeting the needs of the present without preventing future generations from meeting their needs. Dimensions of sustainability: Political, Social, Environmental and Economic. Since the 1990s, new approaches to the management and the mitigation of coastal erosion and flooding have been developed which aim to a more holistic approach to coastal management; involves a more sustainable and long-term approach; considers the coastline; seek to achieve balance between natural processes and human needs and concerns.

Soft engineering:

Beach nourishment:

Description: Addition of sand or pebbles to an existing beach to make it higher or wider. Sediment is usually dredged from the nearby seabed.

Benefits: Relatively cheap and easy to maintain. It looks natural and blends in with the existing beach. It increases potential tourism by creating a bigger beach.

Costs and Disadvantages: Needs constant maintenance because of the natural processes of erosion and LSD. £300000 per 100 metres.

Cliff regrading:

Description: Reduces the angle of the cliff to help stabilise it. Drainage removes water to prevent landslides and slumping.

Benefits: Can be effective on clay or loose rock. Where other methods will not work. Drainage is cost effective.

Costs and Disadvantages: Effectively causes the cliff to retreat. Drained cliffs can dry out and lead to collapse. Cost is variable.

Managed retreat/Marsh creation:

Description: A form of managed retreat by allowing low lying coastal areas to be flooded by the sea. The land then becomes a salt marsh.

Benefits: Relatively cheap (land reverts to its original state before management.) Creates a natural buffer to powerful waves. Creates an important wildlife habitat.

Costs and Disadvantages: Agricultural land is lost. Farmers or landowners need to be compensated. Cost is variable- depending on the size of the area left to the sea.

Dune regeneration/stabilisation:

Description: Marram grass can be planted to stabilise dunes. Areas can be fenced in to keep people off newly planted areas.

Benefits: Maintains a natural coastal environment. Provides important wildlife habitats. Relatively cheap and sustainable.

Costs and Disadvantages: Time consuming to plant Marram Grass. People may respond negatively to being kept off certain areas. £200 to £2000 per 100 metres.

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Landforms and Landscapes of Coastal Erosion.

Bedding planes and joints on a chalk headland are exploited by the sea and widened through hydraulic action.

As bedding planes and joints widen through hydraulic action, they join together and develop into a cave.

Joints from the roof of the cave can be exploited through hydraulic action. When combined with solution from the top of the cliffs, a blow hole was created.

The cave grows deeper and wider by the action of waves as pebbles and boulders are hurled at the roof and sides via abrasion.

Abrasion continues to erode and deepen the cave and can erode all the way through the headland to create an arch.

The arch grows in size through processes such as weathering (e.g. wetting and drying), and exfoliation cause blocks of rock to break off.

As it continues to grow, the top of the arch becomes too heavy and collapses under it's own weight, leaving a stack which is detached from the headland.

The base of stack is undercut through the process of abrasion. This creates a notch around the hole base of the stock.

The stack collapses under it's own weight, creating a stump.

Formation of a wave cut platform:

When waves break against foot of cliff- erosion concentrated close to high tide line, creating a wave cut notch.

As the notch gets bigger, the cliff undercuts and rock above it becomes unstable, eventually collapsing.

Repeat= notch migrates inland and cliff retreats, leaving behind a gently sloped wave cut platform.

Page 14

Sundarbans:

Definitions.

Risk: Chance of danger.

Opportunity: Chance of doing something.

Resilience: Overcoming barriers/ challenges.

Mitigation: Reduce impacts/ challenges.

Adaptation: Changing/ bending to the environment/ situation.

Key characteristics of the area:

Occupies the world's largest delta.

Formed from sediment deposited by three different rivers that flow in the Bay of Bengal:

Ganges, Brahmaputra and Meghna.

Extends over 1000 square kilometres throughout Southern Bangladesh and India.

Network of Tidal Waterways, Mudflats and small islands of salt-tolerant (halophytic) Mangrove Forests.

Climatic Climax Vegetation are Mangrove Forests and Swamps.

Coastal processes that impact the Sundarbans.

Tidal action:

The strong tidal current flows north at high tide and south at low tide twice a day.

This frequent movement of water north to south and south to north creates large, straight channels that are 2km or more wide.

This means that the direction of large channels is north to south.

The tidal action inundates the forest areas with sea water from the Bay of Bengal twice a day.

At low tide, all water drains from the forest areas.

This creates the extensive network of interconnecting smaller channels, known as Khals.

Erosion:

Network of channels are made of clays and silts.

Clays and silts are extremely cohesive therefore are quite resistant to erosion.

The prop roots of the mangrove forests dissipate energy, creating low-energy coastal environments. This reduces erosion from storm surges, currents, waves, and tides.

This means that the interconnected river channels remain static and rarely move.

Deposition:

Mangrove forest prop roots slow the movement of tidal waters, causing sediment to be deposited and build up a muddy riverbed/seabed.

Non-cohesive sediment like sands are deposited on banks at the river mouth.

The south-westerly prevailing wind blows deposited sand into sand dunes.

These dunes act as protection for fine sediment to be deposited further and over time, new islands are developed.

Over time, vegetation is established on these islands which leads to a climatic climax of mangrove forests.

Risks and Challenges for human occupation and development:

Natural:

Coastal flooding.

Cyclones.

High levels of salinity in the soil.

Instability of the islands.

Accessibility and remoteness.

Human-eating tigers.

Human:

Over exploitation of coastal resources from vulnerable habitats.

Conversion of wetlands to intensive agriculture and settlements.

Destructive fishing techniques.

Lack of awareness of the environmental and economic importance of the region.

Resource-use conflicts.

Lack of awareness of coastal issues by decision makers.

Human responses of adaptation.

Increased frequency and intensity of floods: Distributing water tight containers to store important belongings and papers during floods. Salt tolerant rice varieties- survive being submerged for over 2 weeks.

Flood water remaining for longer- Salt tolerant rice variety- survive being submerged for over 2 weeks.

Embankments built by shrimping industry encourages the deposition of silt, raising the river beds and therefore water levels- Grassroots NGOs: education to return to more traditional ecologically friendly methods. 30,000 people received training on improving agricultural techniques.

Rising temperatures contribute to increased salinity in the soil- NGOs build latrines on higher ground and educate communities about water. 30,000 people received training on improving agricultural techniques.

Increased pesticide and fertiliser use is affecting water quality- 30,000 people received training on improving agricultural techniques.

Changes to seasonal patterns of rainfall- relaunch of policy to build multi-purpose cyclone shelters. Also used as primary school resources.