Coastal risks

Topic 3 - Coasts

isostatic change

sea level change that occurs due to the level of the land

• ice = weight causes land to sink, e.g. ice age

• no ice = ice melting allows land to rebound up, rises

tectonic sea level change

land rises/sinks at boundaries of tectonic plates due to tectonic change

• sudden plate movement can lead to a rise/fall in sea bed

• causes sea level change

• can trigger tsunamis

eustatic change

rising and falling of sea levels, influenced by ice ages

• water stored as ice = level dec.

• ice melts = level inc.

emergent coastline

caused by the formation of raised beaches due to isostatic rebound

• original height of land increases

• leaves beach and cliff higher than original position

submergent coastline

• rias

• Dalmatian coast

• fjord

rias

flooded river valley

• form natural herbs

• in lower parts of rivers and their tributaries

Dalmatian coasts

arrangement of rock types parallel to the coast

• sea level rise floods pre existing folds in the coastline

• leaves long narrow islands and sea channels parallel to coast

fjord

flooded u-shaped valley left behind when glaciers erode vertically

• deeper inland than rias

• e.g. Norway, New Zealand, Chile

what is the IPCC

intergovernmental panel on climate change

• acknowledge sea level rise from past and present data

• links it to global warming

CC inc. storm frequency - effects on coast

• stoning storm wind have high energy = create destructive waves (erosional)

• inc. sea energy transports more material, further

• leaves areas vulnerable to erosion if left without protection

• freq. of storm surges will inc., combined with sea level rise surges will go further inland and cause more damage

CC rises sea levels - effect on coast

• from 1901-2010 avg. sea levels inc. by 0.19m

• melting ice sheets e.g. Greenland and antarctic

• higher sea = higher tides - inc. flooding

• higher tides could remove more material from beaches - less cliff protection

global warming evidence

• btwn 1983-2012 - Northern hemisphere hottest 30 years in last 1,400 years

• changes in atmospheric temps is causing thermal expansion of oceans and glacier melting

• largely due to GHG emissions - lots since industrialisation

causes of coastal recession - human

• dredging (removal of sediment) e.g. California - inc. coastal retreat, lower ocean depth, more destructive waves

• hard engineering - starves coastline further down

causes of coastal recession - physical

• weathering and mass movement - combine to increase. recession

• long rainfall weaves rocks - leads to mass movement

• collapsed material eroded and transported away by waves

factors affecting rate of coastal erosion

• weather systems

• tides

• seasons

• wind direction

factors of rate of coastal erosion - wind direction

• controls wave movement

• dominant wind direction = powerful destructive waves

• e.g. SW wind directing waves at Lands end, Cornwall (across Atlantic)

• long fetch has influence

factors of rate of coastal recession - seasons

• higher during winter

• winter - storms = higher tide and long wave fetch

• inc. erosion

factors of rate of coastal erosion - tides

• linked to gravitational pull

• stronger pull = high tide

• weaker pull = low tide

• during high tide, waves reach further inland - can inc. erosion

factors of rate of coastal recession - weather systems

• influence by areas of high pressure = anticyclones - calmer weather, reduces erosion

• low pressure = depressions - unsettled weather conditions, inc. erosion

impacts of CC on coastal flooding

• inc. frequency and intensity of low pressure systems/tropical storms

• rising temps warms ocean - triggers more low pressure systems

• inc. risk of coastal flooding

consequences of coastal recession - economic

• damage to houses and businesses - requires financial support

• in developing countries = limited financial assets, reliant on aid

• developed countries = not enough insurance for potential damages, houses loose value as recession increases

consequences of coastal recession - social

• damage to houses forces people to relocate

hard engineering

strategies that reduce effects of flooding and erosion by building man made structures that control the seas flow

• revetments, sea walls, groynes, offshore breakwaters, rip rap

rip rap/rock armour

piles of boulders placed in front of sea walls to dissipate sea energy and support unstable rock structure

• long lasting

• cheap - £100,000 for 100m

• used for fishing/sunbathing

• don’t fit in with local geology, out of place, danger to climb, very intrusive

offshore breakwaters

rocks placed in a line parallel to the shore - calmer conditions behind breakwater

• effective but permeable

• expensive to install

• visually unappealing, potential navigation hazard, can change wave patterns

sea walls

hard concrete structures that deflect waves, often curved to dissipate the waves energy and reflect it back to the sea

• good long term solution, little maintenance needed, promenade to walk on

• create strong backwash that undercuts the wall, don’t absorb energy, unnatural

• expensive to build and maintain - £6000 a metre

groynes

stone/wood fences hat stick out at 90’ to the coast, stop material transport by LSD

• create wider beaches, slows waves and reduces flooding, inc. tourism

• relatively cheap - £5000-£10,000 each (1 per 200m)

• can starve beaches down coast, more erosion, can be unattrative

revetments

angled walls just offshore to assist breaking down wave force, reducing heir ability to erode the coast

• more cost effective sea wall, reduce erosion rate

• quite cheap - £4,500 a metre

• require regular maintenance, can create access problems to beach

soft engineering

reduces the effects of flooding and erosion by working with natural processes sustainably

• dune stabilisation

• beach nourishment

• cliff regrading

cliff regrading and drainage

restructuring and supporting the cliff to prevent further collapse form weathering/mass movement

• maintains cliff, provides natural environment for wildlife

• cost effective

• risks of further collapse and unintended changes to profile, causes cliff retreat

beach nourishment

the addition of sand or pebbles to an existing beach to make it higher or wider, usually dredges sediment from nearby seabed

• easy to maintain, looks natural, bigger beach = inc. toursim

• cheap, £300,000 per 100m

• needs constant maintenance due to processes

dune stablisation

planting or species like madam grass to stabilise dunes, can fence of areas to keep people of newly planted dunes - restoration of sand dunes to maintain their protection

• natural barrier to flooding, supports wildlife

• cheap £200-£2000 per 100m

• only protects small area, ineffective in powerful storms, time consuming

marsh creation

managed retreat by allowing low lying coasts to be flooded and form a salt marsh

• cheap, land creates natural defence, important habitat made

• loss of agricultural land, land owners need compensation

ICZM

integrated coastal zone management

• holistic approach to management, considers most effective approach for a coast

• considers social, economic, environmental implications

factors considered for ICZM

• risk to residential/commercial/industrial buildings

• implication of coastal erosion to economy

• impact of recession/flooding on natural env.

benefits of ICZM

• promotes consideration of natural env.

• encourages efficient resources use - reduces cost

• tries to reduce loss to stakeholders that rely on coast

shoreline management

• hold the line

• strategic realignment

• advance the line

• no active intervention

SMP - no active intervention

no management used

• physical processes allowed to occur naturally

SMP - advance the line

construction of new engineering techniques to protect the coastline and increase it

SMP - strategic realignment

physical processes allowed to work naturally

• monitoring and intervention only when necessary

SMP - hold the line

maintaining existing defences so they continue to be effective

CBA

cost benefit analysis

• used to determine the economic value of a coastline

• decide if intervention is needed to protect the land

EIA

environmental impact assessment

• assess short and long term implications of sing management strategies on the environment

isostatic subsidence

the weight of ice sheets during glacial periods makes the land sink

isostatic recovery

ice melts at the end of a glacial period, causing the land to readjust and rise

effect off past tectonic activity on sea level

• uplift of mountain ranges and coastal land - destructive/collision margins

• local tilting of land

• e.g. mediterranean ports submerged, but some remain above sea level

terminal groyne syndrome

groynes interrupt flow of sediment along a coast by LSD

• starves beach downstream of material

• leaves cliffs vulnerable to waves

• e.g. Hornsea, Mappleton

ways to deal with flood risk

• adaptation - making changes to lesson the impact of of flooding = sea walls, storm surge barriers, reinstating mangroves

• mitigation - making efforts to reduce GHGs to reduce impacts of climate change

CBA - tangible costs/benefits

where costs/benefits are known and can be given a monetary value

e.g building costs

CBA - intangible costs/benefits

where costs may be difficult to assess but are important

e.g. visual impact of a revetment

coast classification

• geology (rocky/sandy)

• energy level (high/low)

• balance btwn. erosion + depsoition

• sea level changes (emergent/subemergent)

flooding

when the amount of water in a river/channel exceeds the capacity of the channel and it bursts its banks

• water soaks land that is normally dry