coastal flooding (2B.9)

Question 1

why there is disproportionate flood risk

Answer 1

sea level rise affects a disproportionate number of people because:

• many low lying coastlines are densely populated as beaches and the sea attract a large number of tourists
• low lying deltas are extremely fertile and ideal for agriculture
• estuaries and deltas are ideal for trade with good navigable access inland up rivers
• many river deltas support megacities

Question 2

local factors that increase risk of flooding

Answer 2

1. height
   low lying coastlines are often only 1-2m above high tide sea level so greater risk
   - temporary risk from storm surges and permanent flood risk from global sea level rise
   EG highest point in Maldives is 2.3m above sea level, 60% of Bangladesh is less that 3m high above sea level.
2. subsidence
   low lying coastlines in estuaries/ deltas etc are subject to natural subsidence through the settling and compaction of recently deposited sediment
   - human activity can influence subsidence eg weight of the urban environment can also compress sediment leading to subsidence eg Venice
3. vegetation removal
   vegetation such as salt marshes and mangrove forests, refuce flood risk
   - it stabilises existing sediment and traps new sediment raising the height of the land above sea level
   - it also reduces wave imapct by absorbing wave energy EG 1km belt of mangrove can reduce height of storm surge by 0.5m and 100m is estimated to reduce wave height by 40%
4. global sea level rise
   mean global sea level rose by 20cm in the 1900, IPCC predicts a further 18-59cm rise in sea level by 2100.

human factors such as level of development/ population density also play a huge role

! creation of environmental refugees ! a 40cm sea level rise would permanently submerge 11% of Bangladesh, creating 10 million environmental refugees

Question 3

storm surges

Answer 3

depressions and tropical cyclones are low pressure weather systems which creates surges
- the low pressure near eye of the storm pulls water higher, wind pile up water and push it towards shore
! for every 10mb drop of air pressure, sea level is ‘pulled up’ by 10cm ! (DURING CYCLONES air pressure 100mb lower than usual—> 1m rise)

!! coastlines of path of hurricane tracks/ depressions are far more at risk eg in tropics on east coast and mid latitudes on west coast

Question 4

short term impacts

Answer 4

• deaths and injuries to people immediately through drowning or collapsing buildings
• subsequent deaths from hypothermia (homes destroyed), water borne diseases (sewer systems and freshwater pipe destroyed), natural causes (transport routes to medical care cut)
• destruction of infrastructure - roads, railways, ports, and airports flooded or destroyed
• damaged water pipes, electricity transmission lines and sewage systems - no power or water.
• homes destoyed - older houses worse standards, cheap in poor areas - homes on marginal low lying land (slums and shanty towns) most vulnerable - reconstruction may take several years, richer (insurance) likely to be rehoused firs
• businesses destroyed - factories, offices - loss of power, interruption of raw material delivery, workers killed/injured/can’t get there - agricultural land contaminated - crop harvest lost

Question 5

case study (developing): Cyclone Sidr 2007 (Bangladesh)

Answer 5

240kmph winds and 6m storm surges
impact worsened by:
- funnel shape of the Bay of Bengal focussing water on Bangladesh at the bay apex.
- out flowing discharge from the Ganges and Brahmaputra rivers combine with coastal flooding.
- intense rainfall from cyclone increases flooding.
- coastline from unconsolidated delta sediment - easily eroded.
- deforestation of mangrove swamps (globally 1/2 of all mangrove forests have been lost since mid c20th)

10,000 killed and 55,000 injured
1.6 mill. homes destroyed
total damge est.= $17 billion
however the impacts of deathes were much lower than the 1970 Bhola Cyclone where 300,000 were killed. improved warnings embankments anf cyclone shelter networks saved many lives

solution of the poldere embankment schemes lead to yet another risk factor… initially they kept water out but now the land on the inside is subsiding as it is not receiving any sediment deosition form the river (interupting sediment cycle)

Question 6

case study (developed): Storm Xavier 2013, the UK

Answer 6

80+ mph winds, average 3m storm surge but up to 6m in places

impacts worsened by:

• coincided with spring tide
• north sea coastline narrows into a funnel shape for a northerly storm and sea shallows towards coast

2 killed and 18,000 evacuated
coastal defences breached in Yorkshire and Kent and 1400 homes flooded
east coast rail system suspended for 1 day
total economic loss of $100 million

impacts much lower than 1953 storm surge when 307 were killed and economic loss equivilant to $1.2 billion today, due to:

• Thames Barrier which protected 800,000 homes
• improved forecastinga and efficient evacuation

Question 7

environmental refugees

Answer 7

most at risk areas include Maldives, Tuvalu and Barbados
how climate change will create environmental refugees:
- small & narrow economies based on tourism and fishing are affected as sea levels rise and temperatures rise causing coral bleaching and risk of reef destruction.
- water supply is already limited anyways and is now at risk from saly water incursion as sea levels rise and groundwater is overused. no access to drinking water= people forced to leave
- unpredictable weather: drought and increased flooding intensity

Question 8

factors that affect/ increase a storm surges height

Answer 8

• high tide (particulary spring tides)
• shape of coastline: funnels into narrow space (eg bays, Bay of Bengal), surge height increases further.
• sea bed shallows towards coastline= increased height
• time of year