- 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.
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Physical ReasonsHuman ReasonsStormsLack of defences and they can be old and wornLarge WavesHumans living near the coastStorm Surges (from low pressure)Humans increasing the likelihood of flooding e.g deforestation.High tidesLow-lying landTsunamis
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Global/International ReasonsLocal ReasonsCoastalisation and population growthPoor coastal defencesSea level riseTsunami vulnerabilityMore strong waves/destructive wavesSub-aerial processesMore storm surgesCoastal 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.