Second National Infrastructure Assessment: Baseline Report   |   Call for Evidence

Baseline Report Annex C: Flood resilience

Analysis of the country's flood infrastructure and flood risk management systems, informing the Second National Infrastructure Assessment: Baseline Report

Tagged: Water & Floods

Sector overview

Flood infrastructure

Flood infrastructure reduces the risk of communities being flooded when sea levels are high, rivers are swollen or when there is heavy rainfall in built up areas or over saturated or very dry land. It is not possible to eliminate all risk, but flood infrastructure helps minimise disruption to communities, business and other services.

Flood infrastructure primarily aims to protect people from the following types of flooding:

  • Coastal flooding occurs when usually dry land is submerged by seawater. It mostly happens because of a combination of high tides, storm surges and waves.1 Coastal erosion is the permanent loss of land close to the sea
  • River flooding occurs when flows can no longer be contained in river channels and the water spills onto adjacent land. It is generally caused by prolonged periods of intense rainfall2
  • Surface water flooding occurs when the volume of rainfall exceeds the capacity of drainage systems. Water cannot quickly drain away or soak into the ground. Instead, it collects at low points causing flooding.3 Surface water flooding can occur in rural and urban settings
  • Groundwater flooding occurs when water levels in the ground rise above surface levels. It is most likely to occur in areas underlain by permeable rocks.4 The flooding occurs with a delay following a prolonged rainfall and can last for long periods of time. Groundwater flooding is often very localised and there are limited options to provide protection through traditional flood defences.5 Individual property measures are usually needed such as drainage or pumps to divert water away.6

Flood defences include hard engineering assets such as sea walls, embankments and drainage systems. These are complemented by schemes that use natural processes to slow flows or store flood water to minimise the impact of surface water, river or coastal flooding. Flood risk management also entails non-engineering measures such as: floodplain zoning, which helps to avoid inappropriate development in the floodplain; preparing and responding to flood incidents through flood forecasting and warning systems; and increasing the ability of communities to recover following a flood event.7

Responsibility for flood risk management policy is devolved to the governments of Scotland, Wales and Northern Ireland. The Commission’s remit in this area covers England only.

The most comprehensive understanding of flood risk assets is provided by the Environment Agency. It maintains around 77,000 flood and coastal risk management assets.8 These include defences on main rivers, as well as tidal and costal defences and structures. The Environment Agency also inspects a total of 175,000 flood risk management assets, including those it maintains, those of other flood risk management authorities, listed in section C.2, and some belonging to landowners and private individuals which it does not maintain.9

The government has estimated the value of its existing flood and coastal defence assets at £25 billion, which provide an estimated reduction in annual average flood damages of £2.8 billion.10

Properties at risk of flooding

In 2020, more than five million properties in England were at risk of flooding.11 This refers to a total number of properties in areas in all categories of risk of flooding, from very low (less than 0.1 per cent of annual likelihood of flooding), through low, medium and high (more than 3.3 per cent of annual likelihood of flooding).12 These figures account for the existing level of protection by flood infrastructure. The number of properties at risk changes over time due to: pressures from new development; increasing impacts of climate change; aging flood defences that may not have been maintained; or investment in new and upgraded flood defences. Of those properties, 3.2 million are at risk of surface water flooding, which is more than the combined total of 2.5 million properties at risk of river and sea flooding.13 Furthermore, according to the Environment Agency’s research, more than 65 per cent of properties in England are served by infrastructure that is located in areas at risk of flooding.14 However, this does not account for the existing flood resilience measures for infrastructure asset sites.15 Flooding causes great disruption and economic impact to communities. Whilst insurance can cover some impacts it cannot address all the issues such as the wellbeing of communities. Mental health problems can persist three years after a flood event.16

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Status:  Completed

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