5.5 surpluses & flooding

Question 1

5a) meteorological causes of flooding

Answer 1

1. storm (surges) and flash flooding: intensity of rainfall (often caused by depressions- common in the uk) exceeds the capacity of the river to cope with the amount of water eg sept 2016, flash flooding caused travel choas in England as thundertorms deposited half a months worth of rain in some places within hours
2. extreme monsoon rainfall (July- Sept): S. & SE. Asia (India, Pakistan etc) eg 2016 monsoon in Phillipines led to flooding landslides and evacuations in villages north of the captial; worsened by physical conditions, land is made up of floodplanes and deltas from major rivers (Ganges, Padma etc.)
3. snowmelt: occurs a lot in spring eg Russia& Siberia.
4. jokulhlaups caused by volcanoes meltwater beneath ice sheets is suddenly released

WORSENED BY: geology, low lying areas, previous frequent rainfall/ storms saturate stores

Question 2

what human actions exacerbate (worsen) flood risk?

Answer 2

combination of economic and population growth during C20th has caused many floodplains to be built on and many natural landscapes modified for agricultural, industrial and urban purposes: human activities predominantly involves changing land use within river catchements which increases the flood risk but none more so than: URBANISATION!

eg
- impermeable areas such as tarmac
- dams built to supply towns with water
- channelisation to increase area available for farmland
- woodlands intercept rain, roots give good soil structure- deforestation destroys this: rainwater now reaches floodpains quicker, these floodplains are often now made of impermeable surfaces.
- natural grassland allowa water to sink in, destroyed by pasture
- sewers feed water into channel

previously trees absorbed and slowly released water, meandering channels slowed the slow and bogs/ wetlands held the water back

Question 3

river mismanagement by humans

Answer 3

channelisation: effective way of improving river discharge and reducing flood risk howevr it simply displaces the river downstream causing problems for other areas

dams: block the flow of sediment down a river, reservoir grad. fills up with silt and downstream there is increased river bed erosion

river embankments: designed to protect from floods of a given management, they can fail when floods reach their capacity, this is often inevitable and when it does happen the scale of flooding is much greater

using hard engineering intervention to prevent/ protect from flooding is largely unsuccessful: soft engineering is preferable: eg making greater use of floodplains

Question 4

impacts of flooding

Answer 4

socio- economic
- death and injury
- water- bourne diseases
- trauma
- damage to property
- disruption of transport
- interruption of water/ energy supplies
- destruction of farmland and supplies
- disturbance of everyday life

environmental (mention less)
- recharged groundwater stores
- soil replenishment
HOWEVER also negative where environment has been previously degraded by human activity: river banks erode, rivers choked w debris, habitats destroyed, pollutants contaminate food chain

Question 5

flood C/S: Storm Desmond, UK 2015

Answer 5

affected towns on Scottish border, Carlisle, Keswick amongst others: Honister Pass in Cumbria saw 341.4mm of rainfall in the 24hrs up to 18000GMT on 5 DEC 2015
causes?
caused by the deep atlantic low pressure: a warm conveyor that brought long and heavy rainfall.
it was WORSENED by:
- cumbrian fells creating orographic rainfall
- met office said impact was worsened due to consecutive previous rainfall, the intense rain of winter 2015 fell on already saturated land which was steep in gradient
- lots of impermeable surfaces increased rapid flow further

impacts?
socio-economic short:
- 5200 homes were flooded
- 61000 homes lost power when an electrical substation was flooded
- 1000 people evacuated from cumbria
- 40 schools in cumbria

socio-economic long:
- residents forced to live in temp accom
- many residnets suffered trauma
- damage costs were £500 million accross Cumbria (100 mill in 2005, 270 in 2009: an increase!)
- falling of house prices
- flood risk deterred tourists

enviro long:
- river banks eroded
- rivers choked with debris and pollutant
- soils were eroded and habitats destroyed
- pollutants contaminated food chain

human responses: £400,000 donated within 48hrs by public crowd funding, gov issued a full national emergancy response including 200 military & 50 high vol. pumps

Question 6

flood C/S: Kerela Floods 2018

Answer 6

S. West coast of India, lies in the tropical region and is mainly subject to the humid tropical wet climate

causes?
Kereka receives some of Indias highest rainfall in monsoon season HOWEVER unusually intense in 2018 (2346.3mm vs the 1649.55mm avg) due to: spell of low pressure over the region which pulled in south west mosnsoon winds increasing in speed)

impacts?
- flood water became 3-4.5m deep in places
- more than 1 million people left homeless
- total costs of recovery= £2.2 billion (83,000km damaged)
- local plantations were flooded placing local businesses, which relied upon the raw products for trade, at risk.
- schools in all districts closed

Question 7

flood C/S: Cyclone Sidr 2007

Answer 7

a category 4 cyclone in Bangladesh

causes?
low pressure and strong winds HOWEVER worsened by:
- intense rainfall
- high tide in Bay of Bengal (funnel shape too)
- deforestation of mangrices
- 60% of country lessthan 3m above sea level
- snow melt in Himalayas

impacts?
- 1500 killed
- 55000 injured
- 6m strom surges which detroyed 1.6 mill homes
- total damge of $1.7 billion
- 8000km of roads and 700km of electricity cables destroyed

(HOWEVER impacts reduced through improving warning systems, cyclone shelters and emergancy repsonses: the 1970 killed 300, 000 and cost 2.2 bill)