Water- Water surplus, causes and impacts of flooding, EQ2

2 different categories that we can divide causes of flooding into?

Meteorological (physical)

and

human activity

Intense storms and flash flooding: meteorological/physical cause of flooding (how it causes it)

if sudden and high intensity, storms can deposit high vol of rain in a short time

rainfall can exceed infiltration capacity of soil SO causes flooding as ground becomes over saturated and so increases surface run off

EG: 2004 storm(s) in Boscastle meant 75mm of rain occurred in 2 hours which increased river levels and caused flash floods

Snowmelt: Meteorological/physical cause of flooding

in cold/mountainous areas, warming temps (usually in spring-seasonal melt- but increasingly year round) causes snow to melt

flooding due to this can be exacerbated if happens simultaneously with rainfall ext

EG: in eastern europe and the Alps= common as snowmelt and seasonal rains coincide,, After beast from the east snowmelt caused heavy floods in Cumbria

Extreme monsoon rainfall: meteorological/physical cause of flooding

in tropical regions

monsoons can bring high rainand intense and prolonged

reduces the capacity of the rivers and places pressure on the physical and human environment

EG: india’s 2018 kerala floods= driven by abnormally high rainfall caused by monsoons,, 75% of india’s rain occurs during monsoon season

Urbanisation and changing land use: human causes of flooding

urban sprawl and growth=increasing impermeable surfaces (eg tarmac and concrete) SO reduced infiltrations and through flow so increased surface run off

also increases drains and drainage systems which funnels water rapidly back to the river, REDUCING NATURAL DELAYS

deforestation and poor farming practises/management (eg: overgrazing and high compaction from machinery)= reduces infiltrtion and throughflow too

EG:

Mismanagement of rivers:Human cause of flooding

flood defences (eg: levees and embankments and channel straightening)= designed to control river flow BUT can backfire

levees can be weakened and overtopped

channel straightening can increase velocity of the water which can make flooding worse downstream—> doncaster 2019 floods

what is our case study for flooding in the UK esp due to water surplus?

Cumbria

background of Cumbria

incl 2 rivers in the area involved

one of the wettest places in the UK

exposed to air masses from Atlantic Ocean which brings high precip

frequent flooding

around 80% of tenants of a housing association in cumbria flooded had NO insurance—> some of the most vulnerable are those poorest

river greta, river kent

north west england

physical causes of flooding in cumbria

• high relief: The Cumbrian Fells create relief rainfall and increase surface run off > through flow

• Storm Desmond in 2015 (a deep low pressure system/ depression) bought 340 mm rain in 24 hours

• Antecedent rainfall meant soils were already saturated from previous rain ( as a wet november) + steep relief= surface run off is high

• the Jet Stream remained over the north west longer than expected SO moist air massses styed over cumbria for 48 hours→ meaning high rainfall

human causes for flooding in cumbria

• urbanisation: in Carlisle ext,, increases impermeable surfaces ext

• deforestation and overgrazing in upper catchment: eg in lake district,, reduces interception so increases surface run off

• management: embankments on river eden= prevented natural floodplain dev/absorption,, Carlisle’s embankments= cost over £38 mill yet flooding still happens « lots of money, could’ve been spent elsewhere