Characterising flash flood response to intense rainfall and impacts using historical information and gauged data in Britain

Abstract We analyse chronologies of historical flash floods derived from searches of newspaper archives and other sources commencing before 1800 and recent gauged rainfall and stream flow data. Five key examples are chosen to illustrate specific features of flash floods. Pluvial flash floods arise from rainfall before it reaches a watercourse and may cause severe flooding of land and properties far from rivers. River flash floods, like pluvial floods, have the characteristic of rapid speed of response, a principal source of risk to life. Intense rainfall can generate ‘walls of water’ in river courses which can propagate long distances downstream and steepen, without upstream structural failure. Steeply rising wavefronts more commonly occur on steep upland catchments but, where intensities of extreme short period rainfall are sufficient, such wavefronts can also occur on lowland catchments. A definition of flash floods from intense rainfall, relevant to British landscape and climate, is proposed.