PPG: Flood Risk and Coastal Change

PPG: Flood Risk and Coastal Change

What is the sequential test?

The aim of the sequential test is to steer new development to areas with the lowest risk of flooding from any source. Development should not be allocated or permitted if there are reasonably available sites appropriate for the proposed development in areas with a lower risk of flooding. The flood zones are:

Flood Zone 1: Land having less than 1 in 1,000 annual probability of river or sea flooding. (Low probability.) All uses of land are appropriate.

Flood Zone 2: Land having between a 1 in 100 and 1 in 1,000 annual probability of river flooding; or between a 1 in 200 and 1 in 1,000 annual probability of sea flooding. (Medium probability.) The sequential test is needed.

Flood Zone 3a: Land having a 1 in 100 or greater annual probability of river flooding; or a 1 in 200 or greater annual probability of sea flooding. (High probability.) The sequential and exception tests are needed for most uses.

Flood Zone 3b: The functional floodplain (land where water has to flow or be stored in times of flood). Only water-compatible development and essential infrastructure (with exception test) are appropriate.

What is the exception test?

If it is not possible to locate development in a lower-risk zone (after applying the sequential test), the exception test may need to be applied. To pass the exception test:
a) the development would provide wider sustainability benefits to the community that outweigh the flood risk; and
b) the development will be safe for its lifetime taking account of the vulnerability of its users, without increasing flood risk elsewhere, and, where possible, will reduce flood risk overall.

Both parts of the exception test must be passed for development to be permitted.

When is a site-specific flood risk assessment required?

A site-specific flood risk assessment (FRA) is required for:
- All development proposals in Flood Zones 2 and 3
- All development proposals in Flood Zone 1 if the site area is 1 hectare or more
- All development proposals in Flood Zone 1 where there are other known sources of flooding (e.g. surface water, groundwater)
- Development proposals in an area within Flood Zone 1 which has been identified by the Environment Agency as having critical drainage problems

The FRA should demonstrate that the development will be safe for its lifetime, will not increase flood risk elsewhere, and where possible will reduce flood risk overall. It should consider all sources of flooding including rivers, the sea, surface water, groundwater, sewers and reservoirs.

What are sustainable drainage systems (SuDS)?

SuDS are designed to manage surface water runoff from development in a way that mimics natural drainage. They can provide multiple benefits including flood risk reduction, water quality improvement, amenity and biodiversity. The four pillars of SuDS design are: water quantity, water quality, amenity, and biodiversity.

Major developments are expected to incorporate SuDS unless demonstrated to be inappropriate (NPPF paragraph 165). The lead local flood authority (LLFA) is a statutory consultee on surface water drainage for major developments and should be consulted on the suitability of proposed SuDS.

Climate change and flood risk

Flood risk assessments should take account of the potential impacts of climate change on flood risk. The Environment Agency publishes climate change allowances for river flows, rainfall intensity, sea level rise and offshore wind speed and wave height. These allowances should be used in FRAs and reflected in the design of development.