Getting to grips with flood risk management

Planning, 10 August 2007

Flooding is a natural process that performs important functions such as enriching soils around rivers and maintaining natural habitats. But it can create problems where human activities, in the form of agriculture and settlements, are located in areas at risk of flooding. Development on flood plains reduces the capacity of river systems to transport, store and absorb flood waters naturally.

Flooding occurs where the capacity of natural or artificial drainage systems is exceeded by heavy rainfall or high sea levels. Its various forms, including fluvial, coastal, intra-urban and groundwater flooding, can take place in isolation or in combination depending on location, climate and other conditions. Impacts vary according to factors such as the flood's scale and duration and the velocity, volume and type of water, whether fresh water, salt water or sewage. Land use and population level in the area also influence the scale of the impact.

Because of the complexity of managing coastal and fluvial flood risk, the government has identified the need to develop a strategic, holistic approach to the problem. Such flood risk management involves reducing the probability of floods and the severity of their impact when they do occur. Planning is part of an integrated portfolio of engineered and non-engineered responses that also includes enhancing buildings' resilience to floods, issuing flood warnings and creating structural defences.

By influencing the development and use of land, planning presents the opportunity to take a proactive approach to dealing with flood risk issues, beyond simply ameliorating the effects after the event. It also represents one of the lowest-cost options for flood risk management.

Major flooding events in 1998 and 2000 have raised awareness of the risks across all sectors of society. Floods may be getting larger and more frequent for reasons that include modifications to river hydrology and land-use patterns, increased development in areas at risk of flooding, rural land management practices and climate change.

The latter is becoming a key issue. It is predicted that climate change will mean that England experiences warmer drier summers and wetter winters, with more extreme weather events such as heatwaves and intense storms. Such changes would exacerbate risk by, for example, causing more flash floods and increasing the likelihood of coastal flooding from storm surges.

Without changes to current expenditure and policy, it is estimated that drivers such as climate change and urbanisation could increase the financial costs of flooding 20 times to more than £20 billion a year by 2080 and see the number of people at risk of flooding rise from 1.5 million to 3.5 million. Awareness of the current and potential costs of flooding have driven the topic up the policy agenda, leading to reforms of the planning system to tackle the associated challenges.

Jeremy Carter works at the University of Manchester's school of environment and development. This article is an edited extract of a module available in its full, referenced form at www.planningmatters.co.uk, the RTPI's online learning resource.