Flood management: lessons from a US city

The traditional means of flood defence in the UK has been to either increase the capacity of the watercourse or to build barriers between the watercourse and property at risk. The latter approach was used in the city of Grand Forks, North Dakota, USA, but in 1997 the raised defences (levees) were overwhelmed by a flood event with an annual probability of less than 0·5% (i.e. greater than a 1-in-200-year event). Flood management is now superseding the narrower engineered solution of flood defence alone, and while flood management may well include raised defences in some areas, other approaches are also used, as the solution to the Grand Forks flood risk shows. Here large-scale removal of property from one part of the floodplain has prevented that area from incurring further damage and has also provided more ‘space’ for the river in flood times. Differences between the UK and US situations are highlighted, including the type of flood risk, the role of the city engineer, and lessons that can be learned from the Grand Forks example.