2.2- Flooding

Meteorological (physical) causes of flooding

Flash floods, monsoons and snowmelt

Storms and flash floods causing flooding

• occur quickly and without warning

• happen when there’s intense heavy rainfall

• Precipitation is higher than inflitration so runoff is high

Snowmelt causing flooding

• rapid snowmelt increases river discharge

• as soil cant infiltrate as it may still be frozen or snow melts faster than soil can infiltrate

Extreme monsoon rainfall causing flooding

• prolonged rainfall overwhelms drainage basin

• river exceeds capacity due to rain

• saturated soils cant infiltrate anymore, increasing runoff

Human actions increasing flooding

changing land use, mismanaging rivers using hard engineering

Changing land use increasing flooding

• humans change land use from deforestation, agriculture, urbanisation.

• these increase runoff, reducing lag time, increasing peak discharge

• Deforestation reduces interception & infiltration

• Urbanisation increases impermeable surfaces

• More agricultural land reduces vegetation cover, soil compacts reducing infiltration, increasing runoff

Mismanaging river using hard engineering causing flooding

• Dams stops flow of sediment and reservoirs fill with silt, eroding the river bed.

• Channelisation adds concrete liner to straightened river to reduce friction- but displaces river downstream, other areas are affected by flooding now

• River embankments built to improve bank full capacity but if they’re breached, scale of flooding is greater

Causes of Cumbria flooding in 2005,2009,2015

• Storm Desmond caused flooding in Cumbria due to deep Atlantic low pressure system

• Warm moist air was forced up by Cumbria mountains, causing rainfall

• Moist air sat over Cumbria for 48 hours, causing record rainfall & flash flooding

Social impacts of Cumbria’s flood

• schools, shops, offices forced to close temporarily

• residents with flooding homes had to live in temp accommodation

• over 8000 homes flooded

Environmental impacts of Cumbria’s flood

• river banks eroded, adding future flood risk

• saturated ground caused landslides

• rivers contaminated with sewage and pollutants

Economic impacts of Cumbria’s flood

• businesses closed, transport and infrastucture damaged

• cost across the 3 year events was over £800mill

• risk of repeated flooding deterred tourists