GCSE Geography AQA - The Coastal Zone

The coastline is shaped by different processes.

These processes are a direct result of wave action, erosion, transportation & deposition of materials - MARINE PROCESSES.

They are aided by weathering of rocks exposed at coast & mass movement.

Types of mass movement:

• Rock fall - fragments of rock break away from cliff, often due to freeze-thaw weathering

• Landslide - blocks of rock slide downhill

• Mudflow - saturated soil & weak rock flow downhil

• Rotational slip - slump of saturated soil & weak rock along a curved surface

Constructive waves:

• calm weather
• low in proportion to length, less powerful
• responsible for transporting material
• swash stronger than backwash
• arrive at <10 per minute

Destructive waves:

• stormy weather
• tall compared to length, more powerful, high wave energy, large fetch
• remove beach materal - erosion
• backwash stronger than swash
• arrive at 10< per minute

Abrasion/corrasion - cliff worn away when water picks up & hits rocks & sand against it.

Attrition - where rock fragments carried by sea knock against each other, causing them to get smaller & rounder

Solution - some rocks dissolved by seawater, particularly limestone & chalk which form cliffs

Hydraulic action - sheer power of waves as they smash on the cliff, trapped air blasts into holes & cracks, eventually causing rock to break apart. Explosive force of trapped air is called cavitation

Solution - dissolved chemicals derived from limestone/chalk

Suspension - particles carried within water

Saltation - 'hopping' of particles too heavy to be suspended

Traction - large pebbles rolled along sea bed

1. Swash picks up sand & shingle & travels up beach at an angle.

2. Due to gravity, backwash carries material straight down the beach.

3. E.g. prevailing winds in Britain is from south-west so material is moved from west-east along south coast of England

Deposition - occurs when build up of sand & shingle is greater than its removal.

Headlands & bays:

• Bays form when less resistant rock is eroded first & there is deposition in the bay, forming a beach

• Headlands form when more resistant rock is left sticking out, but then erosion begins to take place at the headland

Due to processes of erosion, a wave-cut notch is made at the base of cliff, & eventually the weight of the cliff above is too great so the cliff collapses. This is cliff retreat.

The area under the wave-cut notch is the wave-cut platform.

Cliff features:

• Caves - (hydraulic action & corrasion) formed in weaknesses
• Arches - form when a cave is continually widened
• Stacks - isolated portion of cliff, arch was too heavy so it eventually collapsed
• Stumps - stack is undercut & colllapses to leave a stump, covered up at high tide.

• Beaches - sandy beaches often form in bays; energy of waves reduced as they slow down; crests of waves 'mirror' shape of coastline; waves faster in deeper water & dragged back in shallower water due to friction - WAVE REFRACTION, spreads out & reduces wave energy, why deposition occurs at BAY HEAD BEACHES

• Spits - formed by longshore drift; change of direction in coastline; sea relatively shallow & sheltered; prevailing winds; salt marsh begins to grow behind spit; occasional strong winds from NE turn end of spit; salt marsh is a wildlife habitat

• Bars - a spit that has grown across a bay

• Glaciers & ice sheets melting
• Global temps increase - sea water absorbs more heat & expands
• Affected by rate of global warming

Hard Engineering:

• Sea Wall - barrier to sea, placed at foot of cliffs/top of beach, curved face to reflect back waves, £6 per km, stops sea, can be unnatural, expensive, high maintenence

• Groynes - wood/rock structures, trap material moved by longshore drift, £10,000 each, bigger beach, enhance tourist potential, starve beach down drift, unnatural

• Rock Armour - pile of boulders at foot of cliff, absorb wave energy & protect cliffs, £1-400 each, quite cheap, easy to maintain, can be expensive, don't fit with local geology

• Beach Nourishment - adding sand/shingle to beach to make it bigger, usually obtained locally, £3,000 per metre, cheap, easy, increase tourist potential, need constant management

• Dune Regeneration - effective buffers but easily damaged by trampling marram grass can be grown to help dunes develop, £22,000 per 100m, maintains natural coastal environment - wildlife, time consuming, can be damaged

• Marsh Creation - (managed retreat), allow low-lying land to be flooded by sea, cheap, wildlife habitat, land lost, compensate land owners & farmers

Hurst Castle Spit, Hampshire

• 3km in length
• muddly, pebbly, salt marsh behing in sheltered water
• Moving south-easterly 

• Vulnerable to rising sea levels

• King's Lynn - under threat, valuable agricultural land

• Norfolk Broads - popular for tourism, £5 mil a year, rising sea levels would flood them, destroy local economy

• Erosion rates increase - sea defences will need strengthening, expensive

• 1953 East Anglia - storm surge, killed 300 people, fear it will happen again

• Low-lying mud flats & marshes - Essex vulnerable, 22% could be lost by 2050, managed retreat

• Thames Barrier - will need replacing in next 30 - 50 years

• Natural impacts - low lying country - flooding & cyclones; scientists predict sea could come inland; most vulnerable country to sea level in the world; potentially 1.5m rise; rare species like Bengal Tiger & Wild Boar under threat; reduce freshwater availability; mangrove forests under threat

• Economic impacts - high unemployment; tourism could be lost; one of poorest countries in world; decrease in GDP; loss of agricultural land; loss of roads etc

• Social impacts - densely populated; poor health; famine; cholera; diarrhoea; contaminated water; coastal population displaced; homelessness; loss of agricultural land; communication loss

• Political impacts - increased poverty, forced to seek aid from other countries; whether to spend money on food, health, water, depending on coast; rural to urban migration pressure services; movement of people across borders, tension between India & Bangladesh government

• Swanage Bay - softer clay cliffs, footpaths eroded, litter, sewage outflow; gabian protection - wire baskets filled with stones
• South Haven Peninsula & Poole Harbour - sand dune ecosystem, fresh water marshes, 1mn tourists trample, Poole Harbour threatened by pollution; Studland Heath NNR, National Trust Property, sand dune restoration, Heritage coastline
• Bournemouth - tourist resort, sewage outflow, hotels pressure cliffs, noise & litter; large scale protection scheme, groynes, beach replenishment
• Hengistary Head & Christchurch Harbour - salt marsh, sand dunes, heath, wildlife, harbour suffers from silting & water sports; SSSI - site of special scientific interest, Stanpit Marsh Bird Sanctuary, large groynes
• Christchurch Bay - 30m cliff retreat since 1971, sand & clay cliffs waterlogged, mudflows, landslips, material removed by waves; gabians, sea walls, beach replenishment
• Hurst Castle Spit - formed by eroded cliff material in C. bay, supply of material reduced by groynes, increase intensity storms on spit, breached, salt marsh under threat; AONB - area of outstanding nature beauty, Keyhaven & Pennington, NNR & Bird Sanctuary

Cliffs 30m high, made of sand & clay, recede at rate of 2m a year, some buildings lost to the sea

Cliff collapse:

• permeable sands & impermeable clay, causes water to 'pond up', increases weight, rotational slumping
• attacked by waves, powerful & undercut weak base
• some streams in cliff that add to water in cliffs
• buildings add to weight, interfere with drainage
• made worse by groynes at Bournemouth, beach material cut off

Coastal defences:

• 1965 - 1971 massive engineering scheme, cost over £6 mil
• 1974 - 5 cliff collapsed by 5-10m over 100m stretch
• added limestone boulders, drainage system, rock groynes, artifiicial beach
• some houses only 20m from edge, lost in 10-20 years
• some defences succesful, some failed, made worse by rising sea levels

Mudflats, sand & shingle banks, salt marsh, coastal grassland, sea walls, valuable wildlife, marsh-plant communities, birds, marine life.

Under threat - farmers graduallt reclaiming land, 2500 ha left compared to 16000 ha in 1600, threat of humans from urban development

Strategies - allowing sea to flood large areas, make gaps in sea defences, more saltwater plants & wildlife live there, new low-lying wall to separate from farms; Wallsea allowed to flood by breaching sea defences, making marshes, islands, shallow saline lagoons & creeks, safe - guarding wildlife

Sustainability - sea defences may work for a while, but will eventually be breached - not sustainable; allowing to sea to do what it naturally does, wildlife habitats not at as much risk, work with the sea & not against it

Formed because of Hurst Castle Spit, supports range of habitats - grassland, scrub, salt marsh, reed beds; rich biodiversity

Wildlife - cordgrass, sea lavender, ringer plover, common blue butterfly, wold spider, oystercatchers

How it is under threat - retreating by 6m a year - sea level rise, 'squeeze' of marsh lying between low sea wall & sea; breaching of Hurst Castle Spit in severe storms, exposed part eroded in 3 months; increased demand for tourism, careful management required to prevent trampling, parking, pollution, mooring of boats

What is being done - 1996 rock armour & beach nourishment, increase height of spit, £5 mil sea defences, spit not breached yet; recognised as important site for wildfowl & wading birds, site of special scientific interest (SSSI), natural nature reserve, access limited & development restricted

Big concern of rising sea levels, 6mm a year, 'squeeze' between low sea wall & rising sea.