Physical Geography - Coasts

2 types of waves

Constructive (Swell) and Destructive (Storm)

3 factors affecting wave size

• Wind speed

• Wave fetch

• Duration wind blows for

Crest

Highest point of a single wave

Trough

The lowest point of a single wave

Height

The difference between the crest and trough

Length

The distance between each crest

Period

The time it takes for one wave to travel the distance of one wavelength

Velocity

The speed of the movement of a wave crest

Energy

Wave energy is created when a surface wind is blown across the sea. This provides water molecules with kinetic energy (water pushed up/down) (rippling)

Plunge line

The point at which a wave is going to break

Swash

The body of foaming water than rushed up to the beach when a wave breaks

Backwash

The water which returns down the beach after a wave has broken

Differences between swell and storm waves

• A constructive wave is less frequent

• A constructive wave has a longer wavelength

• Destructive waves are steeper

• Constructive waves leave a gentler beach profile compared to destructive waves

• Destructive waves are taller

• Constructive waves have more swash

How do waves form and break

• The wind blows across the ocean causing friction and small ripples

• These develop into small circular movements in the water

• Waves start in the open ocean

• The height of the wave increases

• The front of the wave becomes steeper

• The upper parts of the wave travel faster than the base

• The wave approaches the coast and the sea gets shallower

• Friction from the sea bed slows the bottom part of the wave

• The wave falls forward and breaks

• The water rushes up the beach as swash

  • It then flows back down the beach as backwash

What 7 processes act along a coastline

1. Transportation

2. Marine Erosion

3. Deposition

4. Mass movements

5. Weathering

6. Earth Movements

7. Sedimentation

Factors affecting rates of erosion

Energy Factors

Material Factors

Shore Geometry

Human Factors

SSSI

Solution → When a load is dissolved in water

Suspension → Particles carried in the middle of the water column

Saltation → Bouncing pebbles along the sea bed

Traction → Heaviest load rolled/dragged along the sea bed

Wave Refraction

Centre orthogonal or wave energy onto the sides of headlands so marine erosion can take advantage of the sides of headlands.

How does deposition occur

Deposition occurs due to a loss or change in energy

Where does wave refraction happen

Cuspate tombolos

Sediment Cell (Littoral)

A sediment cell is a balance between sources of sediment (inputs), transfers of sediment (transportation), and stores of sediment (sinks) in a closed self-replenishing cell

Sediment Cell inputs

Rivers

Beach Material

Mass movements

Alluvial/riverine sediment

Sediment Cell transfers

LSD

Rip Currents

SSSI

Sediment Cell stores

Sand dunes

Beaches

Bays

Banks

How many cells are there in England and Wales

11 Sediment Cells

49 Sub Cells

Sediment Cell for Christchurch Bay

5f

Positive Sediment Budget

Inputs>Outputs → Sediment Surplus (e.g. Deposition and Stabilisation)

Negative Sediment Budget

Inputs<Outputs -> Sediment deficit (e.g. Erosion)

Sediment Cell Disruption - Christchurch Harbour

Flood defences -> Seawalls, revetments and embankments

 

Negative budget (sediment surplus, accretion due to coastal protection)

 

Issue = Siltation (build-up of the fine particulates decreasing the depth of the harbour)

Sediment Cell Disruption - Christchurch Bay

Fine beach materials are found within the bay.

 

Geology = Eocene clays/sands

 

Barton on sea -> revetments, rock groynes, drainage of chines

 

Positive budget as a result of being susceptible to erosion

 

Long groyne has caused a negative budget at Mudeford sandbank -> starvation

Sediment Cell Disruption - Hurst Castle Spit

Important natural defence (positive budget)

 

Spit is now maintained by soft engineering (positive budget -> nourishment)

 

The interruption of LSD due to H.H long groyne, decreasing sediment supply to spit (negative budget)

 

Positive budget = breakwater + revetments

Energy Factors (Factors affecting rates of erosion)

• Wave energy

• Prevailing winds

• Fetch

Shore Geometry (Factors affecting rates of erosion)

• Concordant/discordant

• Beach profile

• Bathymetry

Material Factors (Factors affecting rates of erosion)

• Rocky type (limestone vs iron stone)

• Rock structure

• Porosity vs permeability

• Sediment size being transported

4 Main Cliff Types

Wave Cut Platforms

Vertical Cliffs

Composite Cliffs

Relic(t) Cliffs

Vertical Cliffs

Erosional Landforms: Crack, Cave, Arch, Stack, Stump

E.g.: Ballads Point, Studland

Key Points:

Discordant coastline

Swanage Bay - Headlands + Bays + Wave refraction

Geology = limestone (Chalk)

Chemical weathering -> Carbonation

(Marine Erosion) ACASH

Old Harry’s Rock: Key Notes

Sedimentary landforms

Millions of years of deposition

Fossils with limestone skeletons, warm pre-historic seas

Coccolithophores (CaCo3)

Prone to solution due to weak carbonic acid + Carbonation for rainfall

Sea level change due to ice age

Tectonic forces thrusting the cliff upwards

Chalk more resistant than alternate bands of clay

Wave Cut Notch

occurs between high and low tide marks as a result of marine processes e.g. hydraulic action and cavitation and can lead to the formation of caves. 

Cave

Where notches are widened and deepened by hydraulic action and where there is a weakness in the cliff face. The bigger the weakness (e.g. a fault) the larger the caves.

Blowholes

Vertical shafts linked to the sea through caves at the lower end and come out onto the cliff top.  Caused by waves blasting through lines of weakness or where mineshafts linked to the sea.

Geos

Long, narrow gorge-like inlets, caused by the collapse of a cave roof.

Arch’s

Formed by the wearing away of narrow headlands, especially where there is a back-to-back formation of caves.  They are temporary and eventually collapse.

Stacks

Tall, isolated pillars, free-standing in the sea, occur alone or in groups.  Result from the collapse of arch. e.g. Old Harry

Stumps

Small rocky platforms offshore, may be covered at high tide, formed by undermining of stacks causing their collapse. e.g. Old Harry’s Wife

Wave Cut Platform’s

Rocky platforms extending across the inter-tidal zone, become wider and subject to vertical erosion, may reach an equilibrium where no further downward erosion may take place (unless tectonic uplift or sea level change). The oldest may be extensive and therefore protect cliffs from further erosion.

Composite Cliffs

Composite = Mixture of rock types

Rotational slumping = Barton on Sea (5f)

(soft sands/clays -> Eocene, Pleistocene)

LSD

Porosity of clay slopes = zone of lubrication = slump

Chines

Decrease slope stability, zone of lubrication, rotational slump

Can be managed by cliff drainage

Relic(t) Cliffs

 

2.6 million years -> quaternary period

22,000 years ago we had a LGM (large glacial maximum) - ice sheets + glaciers across UK

Isle of Arran experienced the Devensian glacial period (Scotland NW Hebridean region covered by ice sheet/large glacier)

Ice sheet weighing down on Scotland (Arran)

That is known as crustal subsidence -> land pushed down

As we progressed through to the interglacial period (warming) ice melted, went into the sea

-> Eustatic Sea level rise (sea level change)

Land, starts to feel less of the pressure/weight from the ice sheets, thus rises up (isostatic rebound)

e.g. Isle of Arran

Wave Cut Platforms

Different bands of geology within the cliff face

-> more/less resistant

If the same geology is throughout cliff, the weakness would originate at a fault in the bedding plane or joint

 

WCN starts the process

Further erosion creates undercuts and overhangs -> gravity, weight

Mass movement = rockfalls

e.g. Kimmeradge Bay

Backshore Zone

• Consists of storm beaches - influenced highest spring tide + storm surges driven by high wind speeds

  • Berms are pronounced shingle ridges found on the upper profile of the beach, either sand/shingle

Foreshore Zone

• In between LTM + HTM

• Associated with features such as ridges (more pronounced beach plateaus) + runnels (a dip within the beach profile)

• Ripples within sand

  • Beach cusps are influenced by wave refraction but at the shoreline

Nearshore

• Under-water + exposed to current + wave action (waves likely to spill at this zone) -> can develop breakpoint bars

• One feature that can develop would be a longshore bar

  • Rip currents can develop within the longshore bar

Offshore Zone

• Always submerged

• Offshore bars can be created when circular orbits within waves touch the seabed, depositing/creating a sandy bar

• Barrier beaches can be formed as a result of offshore bars migrating through the littoral zone (Chesil Beach)

Factors affecting beach shape or morphology

Tides - spring tides can influence berm/storm beach creation

 

Waves - destructive vs constructive

 

Sediment supply and type - sediment budget, sand vs shingle

 

Beach shape (minor depositional landforms) - ridges, runnels, ripples, cusps

 

Swash or drift-aligned beaches -> LSD dominant due to a prevailing wind? Or swash dominant?

How are spits formed

Formed by longshore drift, where sediment is transported along the coast by angled wave action. When the coastline changes direction, sediment continues to be deposited, forming a narrow ridge extending into the sea, creating a spit

What is a bar

Depositional landforms that connect across to headlands

Lagoons form behind bars

What is a Tombolo

Tombolo occurs when a spit reaches from mainland to an island via a drift-aligned beach (LSD) e.g. Chesil beach

What is a Cuspate Tombolo

A Cuspate Tombolo is when wave refraction and a swash-aligned beach lead to low energy between the mainland and an island, resulting in deposition and the formation of a spit

Chesil Beach (Tombolo) - Theory 1

Chesil beach has formed as a result of being a drift aligned coast (where LSD is dominant) and material has been carried all the way to Portland isle. (spit connected to the island)

Barrier Beach of Chesil Beach - Submergence Theory

During the LGM, large ice sheets covered the southeast of England, the glaciers eroded via abrasion and plucking to form glacial material. The sea level was much lower because the water was locked up in the glacial ice. As the glaciers started to melt during a period of climatic change, rivers formed and a lot of material was carried into the dry English Channel. Continued melting leads eventually to a rise in sea level (Eustatic change). This water was pushed out to sea and large amounts of sediment built up creating Chesil Beach

How do barrier islands form

• Elongated islands separated by lagoons or inlets

• They would normally form due to waves that have the competency to carry a plentiful supply of material

• They are depositional, thus varying bathymetry/ a low energy zone will cause the dropping of material

• Forming as a result of an abundance of material

• Result of strong/dominant swash patterns

How do offshore bars form

• Formed in the offshore of the littoral zone

• Permanently submarine

• Waves carrying material will dump/drop during circular orbits that touch the seabed

• Bathymetry is likely to be shallower to aid in their construction

• Transportation processes such as LSD and sediment cycling in currents, will cause landforms to grow

 

How do Sand Dunes form

1. Anchorage - the ability of sand to build up and accumulate over time. Plants, driftwood, or rocks, found at the slack line (a line where the sea deposits higher up the beach) will start to accumulate material.

2. Wind energy - this is known as aeolian transport - it can happen in two forms - saltation and surface creep.

3. Large intertidal range (a big beach space/expanse)

4. An abundance of material. The calibre of the grains must be coarse/fine

How does sand move

Wind energy - this is known as aeolian transport - saltation and surface creep.

What are the different stages of the Dune

• Embryo Dune

• Fore Dune

• Yellow Dune

• Grey Dune

• Dune Slack

• Mature Dune

Sand Dune Example

Studland bay

Threats to Studland bay

Litter, storm surges, invasive species, fires (BBQs), Tourism, dune trampling = blowouts

Sand Dune management strategies

• Soft engineering (working with nature)

• Dune fencing

• Beach nourishment

• Establishing anchorage

• Signposts + Tourist placards

• SSSI

• Dorset Wildlife Trust -> conservation/preservation

Conditions needed for estuarine sedimentation

• Intertidal range -> input of muds/silts/sands to help with the sedimentation process

• Low energy environments = deposition dominant process

• Coastal flooding = bringing volumes of material

• Saltwater intrusion - channels cutting through the salt marsh

• Flocculation -> water has a net positive charge, clay/silts negative charge -> they combine, claggy/dense

• Establishment of species -> spartina: grass that traps mud

Factors affecting salt marshes

Weather -> storm surges, high erosional ability, wave type (frequency)

 

River regimes -> fluvial sediment -> to build the saltmarsh

 

Sediment supply -> Salt marsh may struggle to establish

 

Human action -> fishing, tourism, ornithology

How are salt marshes formed

1. Mud and other fine materials begin to accumulate in a coastal region

2. Pioneer species that are tolerant of salinity and submergence begin to develop and trap more mud e.g. Spartina

3. As more mud accumulates and becomes thicker, larger species can grow such as marsh grass and sea lavender

4. The increase in height causes areas of the mud flat to rise above sea level, therefore removing any salt, and allowing complex vegetation to grow

5. These larger plant species slow the current and add dead organic matter, increasing the height up to 25mm/yr

6. As the salt marshes become more developed, moisture-tolerant trees like alder, ash, and oak develop, this is known as the halosere

7. Creek systems develop that allow the tidal waters to come in and out. Any trapped sea water may evaporate, leaving salt pans

Threats to salt marshes (Human)

Industrial pollution - oil plants, factories, nuclear power stations. Impacting our biotic factors - conditions for growth will change as a result of chemicals

Agricultural run-off - using pesticides, herbicides, and fungicides on farmland on the coast, may wash into salt marsh systems, and this will impact the development of species

Overfishing may have knock-on effects on the biodiversity in the saltmarsh

Coastal development for recreational facilities may impact the space in which a salt marsh can establish

Threats to salt marshes (Natural)

Fresh water flooding may impact out salt tolerant species - no pioneers to help with the establishment of the salt marsh

Storm surges/coastal flooding, this will erode the mudflats, removing material and displace our established species

Rising sea levels - likelihood of salt marsh inundation is increasing over time

Keyhaven Salt Marsh: Notes

N+L - At the eastern edge of sub-cell 5f, in lee of Hurst Castle Spit, within Christchurch Bay - Keyhaven salt marsh fed by Avon Water + in the estuary of the Solent

Hurst Castle spit extends about 4km across the Solent - thus Keyhaven is in a sheltered coastal area where deposition and sedimentation can occur.

The marsh has become exposed on the seaward side as the spit has been broken through on numerous occasions due to storm events. A lot of shingle has been taken from the offshore 'shingle ridge' to help replenish the spit and thus protect the saltmarsh

It is a Ramsar site (European recognition of ecological importance) + it is a SSSI

To help protect the marsh, there is rock armour 550m at the beach near Milford

100m rock revetment at the eastern end of HC spit to protect hinge - the distal end

What is a coral reef

Coral reefs are the home of millions of coral polyps, tiny invertebrate animals belonging to the jellyfish family

Location of coral reefs

Reefs are located in between the tropics of Capricorn and Cancer with some anomalies being located just outside those two barriers

Factors needed for coral to grow

Temperature → 23-25^oC

Water Depth → 25m or less

Light → Light supply needed for photosynthesis

Salinity → Less than 30-32 psu

Sediment → Clean clear water

Wave action → Areas of strong wave action but not too exposed

Exposure to air → None as corals will die if exposed to air

Biodiversity value of coral reefs

It is estimated that more than 1 million species of plants and animals are found in a coral reef, including 4,000 types of fish and 400 types of coral. However in the last 25 years the proportion of species has decreased by 30%

Medical treatment value of coral reefs

Coral reef systems can be used as treatment for diseases like cancer and HIV. Half of research to do with cancer drugs is from marine organisms

Tourism value of coral reefs

Tourism in coastal areas can help with the protection of coral reefs as revenue from these areas can be reinvested and help improve the local area as many tourists will be attracted to coral reefs

Coastal barrier value of coral reefs

Reefs create natural barriers, protecting them against damage and breaking power of the waves during storms

Fisheries value of coral reefs

Coral reefs form nurseries for about a quarter of the worlds fish stocks

Types of reef

Fringing Reef

Barrier Reef

Atoll

3 main threats to coral reefs

1. Global warming (Temp/Sea level/Acidity rise)

2. Pollution (Land-based/Shipping/Sewage)

3. Physical damage (Overfishing/Coral blasting/Tourism/Sedimentation/Natural Hazards)

GBR management plan

Zoning within the reef means that different areas of the reef are used for different things, helping the area be more controlled in terms of activities like swimming a fishing, while also allowing areas of the reef to be exclusively used for research

Classed as a UNESCO World Heritage sight

Registered as a marine park

DHW

DHW = Degree heating weeks is when we see sea temps increasing by a degree where coral will not survive. There are genetically mutated red corals that can survive these DHW and it is said that they can survive up to 7x more the DHW

23 DHW in 2020 compared to 0 in 1980

Management Plan: Cross breeding

KAUST: Kingdom of Abdullah University of Science and Technology

What they are doing: Trying to evolve coral to become more heat resistant in a lab so they will be able to survive the increasing sea temperatures. However Petri-dish coral is not exposed to external factors such as sunlight, chemicals, and sea level rise meaning its plan may be limited

Management Plan: Floating Nurseries

Nova Scheme, Maldives

What they are doing: Have created floating nurseries for coral so its depth can be adjusted meaning it can be at the most optimal place underwater to photosynthesise as it reacts to thermoclines and can remove invasive species. This scheme is also very good with eco-tourism as tourism i n the are generates lots of revenue which can be reinvested into coral reef protection

Management Plan: The Red Sea Project

ECO-TOURISM in the Red Sea

What they are doing: Creating high-end sea villas that will encourage the sustainable use of infrastructure for people and generate revenue that can be invested into reef restoration, said to be done by 2030

Management Plan: Coral Vita, Bahamas

Step 1: Micro-fragmentation: Taking a small sample from a reef system and accelerating its growth in a laboratory

Step 2: Assisted Evolution: Putting corals in harsh conditions to try and get them to adapt

 Step 3: Land-Based Farming: Growing large pieces of coral to reintroduce into reefs

Social Sustainability

Not building too many houses and overcrowding an area where it can cause issues

Economic Sustainability

Things such as eco-tourism to help with providing jobs for locals but also helping the local area

Environmental Sustainability

Not overfishing and destroying ecosystems, building around to adapt to current biodiversity

Designated zones for preservation and research

The scientific research behind coral and its tendencies

CBA

Cost benefit analysis -> Land value, impact on people, cost of scheme

EIA

Environmental Impact assessment -> Ecosystems, Human interactions with natural processes

Scheme Duration

Short = 0-20 years

Medium = 20-50 years

Long = 50+ years

What are the different management approaches

Advance the line (Move defences seaward)

Hold the line (Maintenence of defences)

Managed realignment (Land use zoning)

Do nothing (Managed retreat)

Integrated Coastal Zone Management (ICZM)

Mixing both hard and soft engineering plans into an SMP

Vertical Sea Wall

An artificial installation that provides support/protection to either the cliffs or esplanade/street behind

Recurved Sea Wall

An artificial installation that provides support/protection to either the cliffs or esplanade/street behind (recurved top to deflect wave energy)