What are the causes and consquences of flooding?

What are the causes of floods?

• What is a flood?• When do rivers flood?• What factors cause

flooding?• Flooding in Boscastle

case study• What were the causes of

the Boscastle flood?• Homework: what were the

consequences of the Boscastle flood? 2004

Boscastle Flood 2004: Flood factors

• Higher than average rainfall, more rain in one day than normally falls in a month

• Human activity: tarmac’d car park increased surface runoff

• Relief: steep sided valley• Pre-existing conditions: ground saturated by previous

rainfall• Drainage density: small drainage basin, two rivers

(Valency and Jordan) converge, narrow drainage basin, rivers meet in centre of village

• High tide: prevented water leaving the rivers• Soil type: prob. Porous as saturated and collapsed -

landslide

Where will it flood?

• Are areas flood prone?

• Environment Agency flood map

• Rates an area’s risk to flooding

• Includes areas that are defended

Impacts of flooding

• Remember the risk equation?

Risk = hazard exposure + vulnerability - management

Why do the impacts of flooding differ?

• Contrast the impacts of flooding in the UK [Severn and Thames] and SE Asia [Ganges] August 2007