Coastal Systems and Landscapes

the coast as a system

open system

interacts with terrestrial, atmospheric and oceanic systems

sediment cells

sections of coasts

with a defined border (e.g. headlands)

movement of sediment is contained

flows act in dynamic equilibrium

dynamic equilibrium

balanced inputs and outputs

may be upset by human intervention or natural variations

inputs

marine: waves, tides, salt spray

atmosphere: sun, air pressure, winds speed/ direction

humans: pollution, recreation, settlement, defences

outputs

ocean currents

rip tides

sediment transfer

evaporation

stores/ sinks

beaches

sand dunes

headlands and bays

nearshore sediment

cliffs

offshore landforms

transfers/ flows

aeolian (wind) inputs

mass-movement

longshore drift

weathering

erosion

erosion

hydraulic action

attrition

abrasion

corrosion

solution

transportation

traction: large sediment rolls along the seabed

solution: dissolved material is carried

suspension: small sediment is carried

saltation: medium sediment bounces along the seabed

deposition

flocculation (suspended particles flock together)

settling by gravity

energy sources

wind

gravity

flowing water

sediment sources

rivers: majority of sediment from here

cliffs erosion

wind: aeolian transport

glaciers

offshore erosion of landforms

longshore drift: prevailing winds move sediment along a beach

sediment budget

totals gains and losses of sediment

asses the dynamic equilibrium

the littoral zone

cliffs/ dunes area

beyond the influence of waves

changes due to tides/ storm surges and sea level/ human action

sources of energy

sun

waves (main source)

wave formation

1. wind moves across water surface

2. small ripples form in a circular motion

3. seabed becomes shallower towards the coastline

4. circular motion becomes elliptical, leading to horizontal movement of waves

5. wave height increases but wavelength and velocity decreases

6. water backs up and leads to the wave breaking

factors affecting wave energy

strength of wind: larger pressure gradient makes stronger wind

duration of wind

fetch

wave types

constructive

long wavelength

6-9 per minute

low wave height

strong swash, weak backwash

occurs on gently sloped beaches

destructive

short wavelength

11-16 per minute

high wave height

weak swash, strong backwash

occurs in storm events and on steep beaches

negative feedback (waves)

1. constructive waves cause deposition

2. beach becomes steeper

3. encourages destructive waves

4. causes erosion to create a less steep beach

tides

gravity causes tides

tidal range

difference between tide heights

largest in channels such as estuaries

spring tide

largest tidal range

sun and moon in alignment

gravitational forces work together

neap tide

smallest tidal range

sun and moon are perpendicular

gravitational forces work against each other

currents

rip currents occur close to the shoreline

plunging waves cause a buildup of water, forcing backwash under waves

source of coastal energy

can lead to output of sediment

high-energy coastline

more powerful waves (destructive) from a large fetch

rocky headlands and erosion-based landforms

low-energy coastline

less powerful waves (constructive) from a sheltered area

sandy beaches and deposition-based landforms

wave refraction

process by which waves lose energy and turn round a headland

wave energy is focussed on the headland creating erosional landforms

energy is dissipated in bays creating depositional landforms

negative feadback (bays and headlands)

1. headlands form due to erosion of different rock strengths

2. due to wave refraction, wave energy is focussed on headlands, leading to erosion

3. eventually, headlands are worn away, again increasing erosion within bays

corrasion

sediment hurled against cliffs at high tide

abrasion

sediment moved along shoreline, causing it to be worn down over time

hydraulic action

air is forced into cracks in cliffs by waves crashing

high pressure is created, forcing crack apart

solution

acidic seawater causes alkaline rock to be eroded

wave quarrying

waves hit a cliff face and pull fragments of rock away

factors affecting erosion

waves

beach size

activity of subaerial processes

rock faults

rock lithology (physical characteristics)

longshore drift

1. prevailing wind makes waves hit the beach at an angle

2. sediment is pushed at an angle in the swash

3. sediment is pulled back in the backwash perpendicular to the shoreline

4. over time, sediment is carried along the beach

deposition

occurs when sediment is too heavy/ waves lose energy

sediment is deposited in low energy coastline, with low wave velocity

gravity setting/ flocculation

weathering

the breakdown of rocks over time

leads to material transfer in the littoral zone

positive feedback (weathering)

1. removal of sediment is higher than rate of weathering

2. increases area of exposed rock

3. more weathering occurs

4. increases supply of rock for other processes of erosion (abrasion/ attrition)

negative feedback (weathering)

1. removal of sediment is lower than rate of weathering

2. debris builds up

3. decreases area of exposed rock

4. reducing rates of weathering and erosion

mechanical weathering

freeze-thaw: water enters cracks, freezes and expands, causing cracks to develop

salt crystallisation: as seawater evaporates, salt crystals grow over time in cracks and widen them. salt also corrodes ferrous rock

wetting and drying: rocks expand when wet then contract again, causing rocks to break up-

chemical weathering

carbonation: rainwater absors CO₂ from the air to create carbonic acid. this reactes with alkaline rock to make them easily dissolvable

oxidation: exposed minerals will be oxidised, increasing their volume which causes rocks to crack

solution: rock minerals are dissolved

biological weathering

plant roots: exerts pressure in the cracks of rocks

birds: (e.g. puffins) dig burrows in cliffs

rock boring: species of clams secrete chemicals that dissolve rocks

seaweed acids: kelp contains sulphuric acid

decaying vegetation: water flows through decaying plants and becomes acidic

mass movement

down-slope movement of material under the influence of gravity

categorised by creeps, flows, slides and falls

soil creep

soil particles moving downhill

particles rise and fall due to wetting and freezing

forms shallow terraces

solifluction

occurs in periglacial environments

top layers thaw in summer, flowing over frozen layers

mudflows

increase in water reduces friction

mud flows over underlying bedrock

rockfall

sloped cliffs (over 40 degrees)

mechanical weathering

scree builds up at the base of the slope

landslide

heavy rainfall reduces friction and increases mass

a block of intact rock moves down the cliff face

non-curved slope

landslip/ slump

curved slope

land collapses under its own weight

terraced appearance

runoff

water erodes the cliff face/ pick up sediment in the littoral zone

factors affecting weathering

temperature (cold= more mechanical, warm= more chemical)

climate

landforms of erosion

caves

arches

stacks

stumps

cliffs

wave-cut notches/ platforms

headlands and bays

caves, arches, stacks and stumps

1. wave energy concentrated on headlands due to refraction

2. faults in the headland are eroded, forming a blowhole/ cave

3. caves erode through to form an arch

4. unsupported rock above the arch collapses (aided by weathering) to form a stack

5. weathering and erosion turns the stack into a stump

wave cut notches/ platforms

1. erosion concentrated at high-tide mark, creating a notch

2. notch deepens leading to cliff collapse

3. this leaves behind a wave-cut platform

headlands and bays

discordant coastline

softer rock is eroded much faster than hard rock, creating bays

cliffs

steep cliffs: resistant rock in high-energy environments

gentle cliffs: weak rocks prone to slumping in low-energy environments

negative feedback (cliffs)

1. a storm leads to cliff collapse

2. material will be left at the cliff base

3. this protects the cliff from further erosion

negative feedback (wave-cut platforms)

1. wave-cut platform is lenghtened by erosion

2. waves can no longer reach the cliffs to erode the platform further

3. this prevents further erosion

negative feedback (sand dunes)

1. sand is lost during a storm

2. this is deposited in off-shore bars

3. this dissipates wave energy, preventing further erosion

landforms of deposition

beaches

spits

barrier bars

tombolos

offshore bars

beaches

beach accretion occurs due to constructive wave

beach excavation occurs due to destructive waves

swash-aligned beaches: waves approach perpendicular, limiting longshore drift

drift-aligned beaches: waves approach at an angle, so sediment travels (larger sediment found at the start of the beach)

scree near cliff-bases increases angularity of sediment towards to cliff

spits

1. the coast changes direction

2. waves lose energy, depositing sediment carried by longshore drift

3. changes in wind direction lead to a recurved spit

4. multiple curved ends form a compound spit

5. marshes and mudflats develop behind

barrier beaches/ bars

beach or spit extends across a bay to join headlands

water is trapped, forming a brackish lagoon

can form due to rising sea levels

if it is seperated from the mainland, it becomes a barrier island

common in areas with low-tidal ranges

tombolo

bar or beach connects the mainland to an island

formed due to wave refraction off the island, reducing wave velocity

offshore bar

sand is deposited in an offshore region due to lack of wave energy

can become a sediment input

some sediment deposited from backwash

coastal vegetation

roots bind soil and sand together, reducing erosion

plants provide a layer of protection

plants reduce wind speed

sand dunes

wind blows towards the land, carrying sand

large tidal ranges allow sand to dry and be picked up by wind

dunes occur due to vegetation succession: pioneer (resistant) species are able to survive in salty sand, binding it together. decaying organic matter adds nutrients to encourage plant growth

maram grass

pioneer plant

resistant

adapted to reduce water loss through transpiration

roots can grow up to 3 metres deep

can withstand 60 decrees celscius

climatic climax

trees are able to colonise the area

estuarine mudflats and saltmarshes

deposition occurs in estuaries due to low wave energy/ velocity

deposition occurs due to flocculation

pioneer plants trap more sediment

leads to climactic climax

isostatic change

change in land levels (localised)

melting glaciers= isostatic recovery

galcier formation= isostatic subsidence

tectonic activty

eustatic change

change in sea levels (global)

thermal expansion/ contraction

melting/ forming land ice

emergent coasts

where land has been raised in relation to the coast

raised beaches

relic cliffs (showing wave-cut notches etc.)

submergent coasts

where land has sunk in relation to the coast

rias: flooded river valleys

fjords: flooded glacial valleys (deeper)

e.g. the dalmation coast

storm surges

result of low pressure (e.g. from a tropical storm)

risk increased by removing natural vegetation (e.g. mangrove forests) and global warming

risks for coastal communities

• reduced house/ land prices

• economic loss

• damaged environments

• damaged coastal

• 75% of large cities are coastal

hard engineering

man-made structures

aims to prevent erosion

used in high-value areas

soft engineering

works with natural processes

used in low-value areas

groynes

timber or rock structures perpendicular to the coast, trapping sediment from LSD

👍 builds up the beach

👍 cost-effective

👎 visually unappealing

👎 deprives downwind areas of sediment

sea walls

concrete, curved structures that absorb and reflect wave energy

👍 prevents erosion

👍 creates a promenade which aids tourism

👎 visually unappealing

👎 expensive to construct and maintain

👎 wave energy is reflected elsewhere, increasing erosion

rip rap (rock armour)

large rocks that reduce wave energy but allow water to flow through

👍 cost-effective

👎 rocks are sourced from elsewhere so do not fit with local geology

👎 can be hazardous if climbed upon

👎 visually unappealing

👎 can shift in storm events

revetments

wooden or concrete ramps that help absorb wave energy

👍 cost-effective

👎 visually unappealing

👎 needs expensive, constant maintenance

gabions

rock-filled cages at the base of cliffs that absorb wave energy

👍 very cheap

👎 removes places to sit

👎 not long-lasting

👎 can be hazardous if damaged

beach nourishment

sediment is taken from offshore sources to build up the existing beach

👍 builds up beach, protecting cliffs

👍 increases tourism potential

👍 cost-effective

👍 natural appearance

👎 need constant maintenace

👎 dredging disrupts coastal habitats

cliff regrading and drainage

reducing the angle of the cliff to stabilise it and planting vegetation. draining the cliff of excess moisture

👍 cost-effective

👍 natural appearance

👍 reduces risk of harm to life by mass movement

👎 dry cliffs can lead to rockfall

dune stabilisation (with land use management)

planting maram grass and walkways put in place to avoid fenced off areas that are protected from human disturbance

👍 cost-effective

👍 creates a wildlife habitat

👍 walkways can encourage tourism

👎 time consuming

👎 fenced off areas are unappealing

managed retreat

allowing the sea to breach a defense to protect other areas of the coast

👍 can be free

👍 can create habitats

👎 agricultural land targeted and lost

marsh creation

planting pioneer species of vegetation to create low-lying mudflats which stabilise land and absorb wave energy

👍 creates a wildlife habitat

👍 cost-effective

👍 not accessible to walkers which can reduce disturbance

👎 part of managed retreating meaning land may be lost

cost-benefit analysis (CBA)

anaylsis of expected cost vs expected benefits

carried out before any management take place

sustainable coastal management

hollistic strategies which looks at multiple smaller sections of land

• managing natural resources for long-term productivity

• creating new jobs

• educating communities

• monitoring and respoding to coastal changes

• consider all stakeholders

intergrated coastal zone management (ICZM)

large sections of coastline managed under one strategy, over political boundaries

• sustainable, prioritising environmental conservation over economic development

• involves all stakeholders

• should not prioritise one community over another

shoreline management plans (SMPs)

each UK sediment cell has an SMP, identifying all human and non-human activities in the coast

• hold the line

• managed retreat

• no active intervention

• advance the line

considers economic, engineering, ecological and cultural values

conflict over policy decisions

communities can feel at a loss due to cultural significance of land/ practices

home and landowners losing property