Introduction

Floods are one of the world's most damaging and dangerous natural hazards. Jonkman (2005) estimated that, in the last decade of the twentieth century, fluvial and other drainage-related floods killed 100 000 and affected 1.4 billion people. Economic losses from floods are difficult to estimate precisely, but are large and increasing. Barredo (2009) estimated annual average losses for Europe to be $3.8 billion over the period 1970–2006 (at 2006 values), and UNESCO (2009) noted that losses from extreme events rose 10-fold between the 1950s and 1990s in real terms. Flood protection and flood management are therefore seen as important issues by society, and associated infrastructure and management systems represent large and ongoing investment (in the UK, annual expenditure on flood defence is of the order of £800 million).

However, flood risk management is a complex and multi-faceted issue. Floods are part of the natural functioning of fluvial systems. This has important implications. Firstly, to understand flood response and to manage flood risk, there is a need for awareness of the nature of and controls on catchment response, including the effects of human interventions. Secondly, floods are essential for the maintenance of aquatic and riparian habitats, and hence a holistic assessment of flood management is necessary, including broader environmental considerations such as geomorphological and hydro-ecological aspects. There may therefore be tensions between the need to protect infrastructure and risk to life on the one hand and the need to maintain natural ecosystem function on the other.