Chapter 2: Flood risk

Flooding is a natural phenomenon, where water flowing towards or out of a waterway inundates normally dry land, generally due to the influence of weather systems.

Flood behaviour varies substantially between and within floodplains and flood events. It can be caused by water overflowing from waterways as well as water flowing overland into waterways. The main channels of waterways generally only convey more frequent flows. In significant events, floodwaters are generally conveyed in both waterways and floodplains, which have many different shapes and sizes, from broader floodplains in flat areas to more incised floodplains and waterways in steeper areas. In addition, the catchment areas of these floodplains vary substantially: from relatively small catchments that may flood within minutes or hours of a storm event, to large catchments where flooding may occur days, weeks or even months after a rainfall event, and in some cases well away from where the rain fell.