2B.9 Coastal Flooding Flashcards
give two example countries that are vulnerable to coastal flooding and why
Bangladesh and the Maldives
-due to their low lying land
-places are densely populated as beaches and the sea attract a large number of tourists
-low lying deltas are fertile and ideal for agriculture (Bangladesh)
how can height be a factor for coastal flooding?
-low lying coastlines are 1-2 m above high tide sea level
-temporary flood risks from storm surges and permanent flooding from global sea level rise
how can subsidence be a factor for coastal flooding?
-estuaries and deltas are subject to building and natural subsidence through the settling and com[action of deposited sediment
-human activity can cause local subsidence- via sediment drainage
how is Venice experiencing subsidence?
due to the weight of the city area and ground water abstraction for supplying cities, reducing sediment volume, leaving the ground to slowly sink
-sinking by around 1mm a year due to natural processes, humans are accelerating this though
how is the Fens of East Anglia experiencing local subsidence?
due to the drainage of saturated sediment and soil for agriculture
-currently protected by coastal defences, already much of it lies below highest tide levels
how is removing vegetation be a factor for coastal flooding?
it increases the vulnerability, as wave energy is dissipated less e.g. salt marshes and mangrove forest removal
-they stabilise existing sediment and trap it, raising height above sea level
Bangladesh sea level rise statistics
a 40cm rise would permanently submerge 11% of Bangladesh, creating 7-10 million environmental refugees
Maldives sea level rise statistics
a 50cm rise would permanently flood 77% of the Islands’ local area
Maldives main facts
has a population of 400,000 people, spread across 1200 islands
-highest point is 2.3m above sea level
-therefore very vulnerable to storm surges and erosion if levels rise
-removal of mangroves has increased flooding risks
Bangladesh main facts
one of world’s most densely populated countries
-46% of population live less than 10m above sea level
-people live in a delta of rivers, in the Bay of Bengal
-experiences heavy deforestation and monsoon on low-lying land
-subsidence has caused islands to sink by 1.5m in the last 50 years
The Thames Barrier in London
-one of the largest movable flood barriers in the world, spanning 520m across the river
-it protects 1.4 million people and 420,000 properties
-high rainfall has produced more prolonged flows
what can storm surges cause?
severe coastal flooding with dramatic short-term impacts
how are storm surges formed?
low pressure causes surface of the sea to rise temporarily
- surface winds spiral into the centre of the low pressure, causing depressions
storm surge
a temporary rise in local sea level produced when a depression, storm or tropical cyclone reaches the coast
named UK storm surge example date and location
5th December, 2013 in coastal East Anglia
-impacted Norfolk, Suffolk and Essex
December 2013 UK storm surge about
-the low pressure stream passed in the North Sea, near North Scotland
-29 severe flood warnings, 141 flood warnings and 63 flood alerts issued
-area of low pressure crossed the top of North Sea, pushing water southwards, causing sea levels to rise more over the shallow sea bed
-water was pushed into a narrow space, increasing wave height, with decreasing depth
how does coastal morphology play a significant role in storm surges?
a shallow coastline slope produces a greater surge than a steeper slope, as the waves push the water inland faster than it can drain off via backwash
name factors affecting the impact of a storm surge
-pressure (low pressure makes a higher surge)
-storm intensity/ wind power
-size of storm
-angle of approach (perpendicular is higher surge)
-shape of coastline (concave is higher surge)
-width and slope of ocean bottom
-local features e.g. barriers affecting flow of water
how can winds and tides impact storm surge
-high winds ‘whip’ up waves causing them to be large and powerful
-high tides cause sea levels to be higher than normal- this is a natural factor
impacts of Storm Xavier (Dec 2013) on the UK
-£1bn damage estimated across Norfolk, Suffolk and Essex
-80mph winds
-2 people died, 18,000 evacuated
-properties collapsed into the sea from erosion
-1400 homes flooded
-bridges shut and eastern railway services disrupted for a day
-£100 million total economic loss estimate
cyclone in Bangladesh name and date
Cyclone Sidr in November 2007
cause of cyclone sidr
low pressure (depression) sustems and high wind speeds
about cyclone sidr
-category 4 cyclone
-240kmph winds
-6m storm surges
impact was worsened by intense rainfall, coastline from unconsolidated delta sediment is easily eroded, deforestation of mangrove swamps
impacts of cyclone sidr
15,000 people killed
55,000 injured
1.6 million homes destroyed
-$1.7 billion total damage estimate
-roads, electricity lines, fresh water tube wells and crops destroyed
