COASTAL FLOODING: PHYSICAL CAUSES.
- LOW PRESSURE ATMOSPHERIC SYSTEMS: e.g. hurricanes (cyclones) reduce atmospheric pressure on sea surface, causing it to rise - a STORM SURGE.
- STRONG ONSHORE WINDS: can force water to higher levels along the coast, allowing waves further inland.
- TIDAL CURRENTS & SURGES: may be funnelled into a coastal bottleneck.
e.g. Bay of Bengal - rising sea level.
- HIGH RAINFALL: may increase river discharge.
If the sea level at the mouth is high, perhaps due to high spring tides/storm surges, a large volume of river water may be unable to drain into sea, causing flooding.
- WHEN A COMBINATOIN OF ABOVE FACTORS COINCIDE: e.g. hurricane making landfall in Florida can cause storm surge & high rainfall.
Storm Surge & wave energy may be intensified by strong onshore winds.
- TSUNAMIS: huge ocean waves caused when water is displaced by landslides, volcanic eruptions or submarine earthquakes that shift the ocean's floor.
When travelling in open water (at sea), wave height = very small & waves travel at hundreds of km an hr.
As the waves approach the coast, the bottom of the waves slow, due to friction with the sea bed, causing wave height to increase hugely.
COASTAL FLOODING IS CAUSED/INTENSIFIED BY HUMAN AC
- MANAGEMENT OF RIVER SYSTEMS:
e.g. dams trap sediment therefore reduce the amount deposited at the mouth.
This causes deltas & salt marshes to shrink, providing less protection against high tides & storm surges.
- BUILDING ON COASTAL LOWLANDS
especially sand dunes, has restricted sediment supply to protective beaches & marshes.
Development of coastal lowlands e.g. FLORIDA = increase impact of any coastal floods.
- MANAGEMENT OF COASTAL SYSTEMS
some alter sediment movement, reducing amount of protective beach material further along coast.
e.g. coastal defences @ Barton, Hampshire = reduced sediment transport to the East, allowing Hurst Spit to be breached more often, flooding lowlands behind.
- RECLAMATION OF COASTAL LOWLANDS
e.g. Dutch polders & reclaimed marshes along East coast of England.
Draining this land to reclaim it, causes land to shrink & become lower than sea level.
COASTAL FLOODING CASE STUDY: TSUNAMI 2004.
TSUNAMI, SOUTHERN ASIA: 26th December 2004.
- Devestated areas of Indonesia, Sri Lanka, Thailand & India.
- Caused by submarine earthquake in Indian Ocean (9.0 on Richter Scale)
- Countries most affected:
Tsunami travelled across Bay of Bengal at speeds up to 800 kph.
Waves struck south-eastern India just 2 hrs after quake.
Tsunami reached more than 2km inland @ Trincomalee in NE of Sri Lanka.
Epicentre was off the western coast of Sumatra, Indonsia.
Waves up to 30m high struck Indonesian insland, Sumatra, within mins of quake.
TSUNAMI'S SOCIAL IMPACTS
- Deadliest tsunami ever recorded.
- Estimated 230,000 killed or missing.
- Approx. 1.7 million made homeless.
- Many fresh drinking water sources polluted, either by sewage or saltwater.
- Estimated 400,000 lost jobs in Sri Lanka alone.
- Estimates of cost of initial damage: between $8 billion - $15 billion.
- Fishing = large part of economy for many areas:
Boats, nets & other equipment destroyed/lost, affecting fishermens' livelihoods.
- Salinisation: (increased salt content) of land severely damaged fertility of soil.
Crop production will be lower for many years to come.
- Tourism = important to economy.
25% Southern Thailand's hotels closed for at least 6 months, due to damage.
Number of visitors to island of Phuket decreased by 8-% in 2005, due to the area been seen as less safe.
- 8 million litres of oil released into environment after 2 oil plants in Indonesia were destroyed.
Caused widespread pollution at sea & contamination of soil
= health risks to humans in the area.
- Mangrove forests as far away as East African coast were damaged by force of waves or were covered in layers of silt.
- High salt content of floodwater destroyed the natural balance of many ecosystems.
e.g. Karagan Lagoon, southern Sri Lanka.
HUMAN ACTIVITY WORSENED THE IMPACTS
- Mangrove Forests protected parts of Sri Lankan coast by absorbing wave energy.
BUT, pressure for tourist development & the creation of prawn fisheries has led to the destruction of Mangrove Forests in other areas around the Indian Ocean.
Its estimated that Thailand has lost up to 1/2 of its Mangrove Forests since 1975.
Lack of protection meant that the waves could reach further inland & flooding was much worse than areas protected by Mangroves.
- Its thought that healthy coral reefs surrounding the Maldives acted as a breakwater (reducing power of waves)
& that they prevented coplete destruction of the low-lying islands.
HOWEVER: illegal coral mining & use of dynamite in explosive 'blast fishing' has destroyed many offshore coral reefs in the Indian Ocean.
= reduced level of natural protection from waves.