Coasts

Features

Wave length – distance between top of waves
Wave period – no. of waves per min
Beach profile – angle of slope of beach

Processes of erosion

Hydraulic action – force of waves trap & compress air in cracks in rock & wear away loose materials
Abrasion – loads carried by waves collide & wear away cliffs
Corrosion – acid in water reacts and dissolves carbonation rocks & carries away in solution
Attrition – load carried by waves collide with each other, become smaller and smoother
Marine erosion – wearing away of cliffs by waves

Types of waves

Destructive waves	Constructive waves
Large, high wave height, short wave length & high frequency Swash weaker than backwash More sediment removed from beach than transported in Erodes beach Steep beach profile	Small, low wave height, long wave length & low frequency Swash is stronger than backwash More sediment transported onto the beach than removed Beach is being built up Gentle beach profile

What causes a wave to break at the coast?

Wave approaches coast in same direction as wind is blowing
Sea floor becomes shallower
Wave base slows down coz of friction with sea floor
Wave becomes higher and top of the wave breaks eventually
Water flowing up the beach in the same direction as wind is blowing (swash)
Gravity causes water to flow back down the beach to the sea (backwash)

Landforms

Bays and Headlands

Formation

Alternate bands of hard and soft rock along coasts
These rocks erode at different speeds (differential erosion)
The softer rock e.g. clay erode faster & form the bays.
The harder rock e.g. chalk erode slower & form the headlands.

Explain how differences in rock type can lead to formation of bays and headlands. (2)

Different in resistance (hard & soft rock), differential erosion, discordant coastline

Cliff and wave-cut platform

Characteristics

Cliff – Hard rock, steep, high, jagged, vegetation covered near top

Wave-cut platform – Hard rock, gentle sloping, contains joints, located at base of cliff

Formation

Bottom of the cliff is eroded by hydraulic action & abrasion by waves
Cliff is undercut, making a wave cut notch
Cliff above is unsupported & eventually collapse
Cliff will retreat backwards
Material on beach will be broken up by attrition & removed by the waves
Process repeat itself, causes cliff to retreat & leaves gentle slope of rock called wave-cut platform

Caves, arches, stacks and stumps

Characteristics

Stack – Rocky, hard, tall, narrower base, wider top, surrounded by sea, layers of rock

Arch – Rocky, steep slopes, joints, shape of bridge, jagged

Formation

When waves crash against the rocks, a line of weakness in the rock eg crack is eroded
Line of weakness enlarges, form a cave
Cave is eroded through the headland to the other side, form an arch
Roof of the arch weakened by erosion and collapse leaving an isolated rock in the sea called a stack
Over time the stack will be eroded by the sea and become smaller to form a stump

Longshore drift

Waves flow in the direction of the wind
Swash deposits sediment on the beach at an angle in the direction of the wave
Backwash returns at right angle due to gravity
Beach material gradually move along the beach in a zig-zag motion

Landforms made from longshore drift

Spit

Characteristics

Long and narrow, made of sand or shingle, one end attached to the coastline & other end open water

Formation

Sediment carried by longshore drift… (explanation)
At a bend or break in the coastline, longshore drift continues to transport the material & deposit material in open water → form spit
Change in wind direction cause longshore drift to change the direction of sediment movement → form hooked end
Area behind spit is sheltered from waves & wind, deposition occurred. Deposited material colonized by vegetation eg halophytes. Their roots trap more sediment → form salt marsh behind spit.

Bars

Characteristics	Long and narrow, both ends attached to the coasts, water behind bar (lagoon)
Formation	Spit grow across river mouth till reaches the other side of land Water behind bar becomes trapped, form lagoon Eventually, sediment fill up lagoon.

Tombolo

Characteristics	Long and narrow, one end attached to coast/island
Formation	Spit grows from coast to an offshore island

Sand dunes

Conditions required (SWOP)

Sand – large supply of sand
Wind – strong onshore wind to dry out and transport sand
Obstacles – eg seaweed on beach trap sand
Plants – halophytes eg marram grass colonize dunes
Flat land

Formation

Sand dries out
Onshore wind pick up sand from beaches particularly at low tide
Sand deposited around obstruction
Sand builds up over time → form dunes
Halophytes eg marram grass colonizes dunes

Beach

Formation

Powerful swash moves material up beach by constructive waves
Weak backwash doesn’t have energy to remove material
Beach material builds up over time
Larger material carried further up beach
Longshore drift
Gentle slope reduces speed, causes sedimentation
Deposition in sheltered bays

How the beach material changes along the transect from the sea to the cliff?

Sand near the sea
More shingle in the middle section
Lots of large pebbles near the cliff

Coral reefs

Created by many polyps (tiny animals that live in colonies, eat zooplankton & get energy from photosynthesis for algae – gives corals colors
Produce CaCO₃ to form solid structure for protection
Provide protection & food source, creates biodiverse marine ecosystem

Characteristics

Plants
lots of variety of species eg fishes & turtles
colourful

Conditions required

Warm water, + 20°C
Shallow water, no more than 60 m deep
Clear water / plentiful supply of oxygen & light
Plentiful supply of plankton
Calm seas
High PH

Types of coral reefs

Fringing reef

grows in shallow water around coast
attached to coast
forms narrow reef parallel to coastline

Barrier reef

offshore
separated from coast by lagoon
wider, older, larger than fringing reef

Atoll reef

roughly circular surrounding a deep central lagoon
form around submerged volcanic islands coz convection current
polyps build coral structure upwards

→ maintain light condition for photosynthesis

Opportunities

Fishing industry – contain many fishes – seafood / commercial fishing
Tourist industry – biodiverse, beautiful scenery attract tourists scuba diving, creates job opportunities
Coastal defence – protect coastlines from tsunamis by absorbing wave energy

Threats (eg coral bleaching)

Climate change – polyps die when sea temp ↑
Sea water pollution eg oil spills – polyps die
↑ pH of sea water coz acid rain & air pollution
↑ sedimentation coz river deposits more loads to sea – ↓ light & oxygen levels
Disease – viruses infect & kill polyps

Mangrove swaps

Characteristics

Salt tolerant
Evergreen trees
Salt filtering
Grow between high & low water mark

Conditions required

Warm temperature, 24°C
High annual rainfall, +1200mm
Sheltered coastal area – low wave energy
Wide gentle slope with large tidal range

Opportunities

Fishing industry – contain many fishes – seafood / commercial fishing
Coastal defence – protect coastlines from tsunamis by absorbing wave energy
Breeding ground for marine life – coral reefs depend on mangroves to breed, important in ecosystem
Filters pollution – clean sea water, protect coral reefs from pollution

Threats

Destroyed for land for agriculture eg prawn farms
Over-logging for woods

Coastal impacts

Coastal erosion – cause properties to collapse / damaged eg loss of farmland
Natural disasters eg coastal flooding, storms, tsunami → damage port installations
Danger to ppl from collapsing cliffs
Cost of protection measures
Unable to sell properties

Management of coastal impact

Hard engineering methods

Types	Description	Adv	Dis
Groynes	Barriers built at right angles to the beach to trap sediment and prevent longshore drift	Cheap Prevent longshore drift	Cause erosion on downdrift side May rot away Doesn’t protect cliff
Sea walls	Large-scale concrete curved walls built along base of cliff	Long-lasting Reflect wave energy High protection	High production & maintenance costs Destroy habitats eg nesting sites for sea birds Waves reflecting off wall can scour beach
Offshore breakwaters	Built out into the sea, enable waves to break on breakwaters	Cheap Tires don’t have to be dumped elsewhere	Disrupt local ecology Technically difficult to install Visually unattractive
Revetments	Barriers built mid-way up the beach and parallel to the sea	Cheap Easy to build	Needs regular replacement Weak – doesn’t protect against storms Short life span
Gabions	Large boulders placed in cages	Installed quickly Fairly effective	Expensive Visually unattractive Small scale
Rock armour	Giant boulders placed at base of cliffs	Effective	Expensive Visually unattractive Small scale

Soft engineering methods

Types	Description	Adv	Dis
Beach nourishment	Adding sand to the beach to replace eroded sand	Looks natural	Short life span
Planting vegetation	Planting of mangroves Vegetation on slopes	Looks natural	Not effective

Case study – Criccieth, West Wales coast

Basic info

Formation

Granite & basalt forms headlands of Criccieth castle & Black Rock
Boulder clay eroded faster to form Criccieth Bay

Opportunities

Tourism – attractive coastline eg wide sandy beach & Black Rock caves
Job opportunities eg restaurants
Easy access eg Cambrian Railway
Fishing – small scale, mostly recreational
Agriculture – surrounding land used for postal farming

Hazards

Glacial deposits eg Boulder clay – retreat 1m every 10 years
Exposed to 4000km fetch from Brazil, prevailing wind: SW
Strong waves erode weak rocks
Raising sea level
Threats to businesses, residental areas & farmland

Management

West of Wales Shoreline Management Plan

Encourage provision of adequate flood warning systems & coastal defences measures
Discourage development in areas at risk from flooding / coastal erosion

Coastal defence measures

Breakwater – on western side, made of concrete, protect lifeboat station, £500,000
Rip-rap – made of boulders, protect cliff
Victorian / recurved sea wall – made of granite, protect open space
2 Groynes – stop longshore-drift, £90000 for 2