Coastal Landscapes - Coastal Flooding

  • Coastal flooding occurs when normally dry, low-lying land that is flooded by seawater.
  • Caused by an area becoming submerged in water causing river banks to burst or to begin to coastal flood.
  • Sometimes, rivers and coastal flooding can combine e.g around estuaries or on a delta. If there are a storm high tides and heavy rain, coastal areas and river waters can flood the land e.g Hull and the Holderness Coast.
Physical Reasons
Human Reasons
Storms
Lack of defences and they can be old and worn
Large Waves
Humans living near the coast
Storm Surges (from low pressure)
Humans increasing the likelihood of flooding e.g deforestation.
High tides
Low-lying land
Tsunamis
Global/International Reasons
Local Reasons
Coastalisation and population growth
Poor coastal defences
Sea level rise
Tsunami vulnerability
More strong waves/destructive waves
Sub-aerial processes
More storm surges
Coastal defences changing the dynamic equilibrium.


Case Study – Bangladesh:
  • Low-lying estuarine land as the Ganges River Delta
  • Large storm surges due to tropical storms
  • River flooding from monsoon rain increases water build up in estuaries areas.
  • Deforested Mangroves trees mean less natural protection from waves leading to a build-up of erosion and less coastal protection.
  • Subsidence due to sediments being deposited on land which rises land level
  • Sea level rise due to global warming
Storm Surges:
  • A temporary rise in sea level due to low-pressure storm systems (depressions).
  • Cause: Low pressure causes sea level to rise and strong winds to blow bulges of water against the coast
  • Worse when they occur with a high tide of flooding is more likely
  • Can rise up to 2m high in Eastern England
  • 5m high during Typhoon Haiyan
  • Its’ severity is often increased due to strong onshore waves and winds.
Climate Change Increasing Coastal Flooding:
  • A eustatic sea level rise
  • Increases coastal flooding globally because climate change is increasing the energy in the atmosphere
Why Does More Flooding Occur:
  • Magnitude and the frequency of storms is higher = more storm surges
  • More powerful waves and winds occurring more often
  • Sea level rise around 20cm over the last 100 years leading to more natural coastal flooding
  • Storm surges and destructive waves are more common
Where Is Affected The Most By Coastal Flooding:
  • Bangladesh – low-lying deltas and storms
  • Philippine – typhoons with a big magnitude and frequency
  • Maldives – small low lying islands
  • Netherlands – land is already below sea level
Mini Case Study – Maldives:
  • Eustatic sea level rise
  • Low lying, high-density population, limited sea defences, no high ground, directly below sea level.
Mini Case Study – Netherlands:
  • ¼ is already below sea level
  • Has the worlds best sea defences, hard engineering of sea walls and gates for high tides.
Summary:
  • More people live on coasts due to migration and population growth therefore flooding risk is higher than ever.
  • Storm surges are the biggest reason for coastal flooding of high magnitude
  • Local coastal flooding due to deforestation and subsidence
  • Global warming is increasing the risk of flooding due to eustatic sea level rise
  • Bangladesh has been hit by storm surges = floods
  • Most at risk are low lying areas and islands close to the sea
  • Lots of uncertainty over sea level rise.
at