The Flood Risk and Coastal Change PPG defines functional floodplain as “land where water has to flow or be stored in times of flood” (PPG Table 1 in Paragraph 065). The PPG states that the extent of the functional floodplain, also known as Flood Zone 3b, should be defined by LPAs within their SFRAs. This allows for the incorporation of local circumstances and must be agreed with the EA and the boroughs’ LLFAs.
PPG Paragraph 015 states that the functional floodplain is usually defined, as a minimum, as land which would naturally flood up to and including a 1 in 20 year return period event or designed to flood in 1 in 1000 year events. Flood storage areas designed to protect downstream communities from flooding should also be included in the functional floodplain. This ensures that land that is required for current or future flood management features can be safeguarded from development, directly aligning to Paragraph 100 of the NPPF. The area identified as functional floodplain should take into account the effects of defences and other flood risk management infrastructure. Areas which would naturally flood, but which are prevented from doing so by existing defences and infrastructure or solid buildings, will not normally be identified as functional floodplain – further clarification of this is provided below in Section 3.11.2.
This SFRA adopts a definition for Flood Zone 3a that includes fluvial, tidal and surface water flood extents as described in the bold text boxes below. The extents are shown in the Web Map. The mapping extents have been split to aid applicants and the LPA through highlighting the flood risk source(s) which a site may fall within. The policy requirements are identical regardless of the flood source.
The Flood Zone 3b (functional floodplain) definition is adopted to ensure that future development is steered away from the most ‘at risk’ flooding extents from fluvial and tidal sources. The Flood Zone 3b definition within this SFRA does not include surface water flood risk, but it should be noted that a policy recommendation is made in Section 5 that may be adopted by some boroughs that could impose additional requirements for developments proposed within Flood Zone 3a (surface water) and the 1 in 30yr RoFSW extent.
The surface water mapping used, the Risk of Flooding from Surface Water (RoFSW) map published by the EA, is the most consistent and representative data currently available. Further information about this dataset can be found in its associated November 2013 guidance note (note that the published name for the Risk of Flooding from Surface Water map was previously the ‘updated Flood Map for Surface Water’ – the underlying dataset is the same).
Flood Zone 3b (Functional floodplain) is defined as:
• Land within EA modelled fluvial and tidal flood risk extents predicted for up to and including 1 in 20 year return period events allowing for the impact of flood defences – Flood Zone 3b (fluvial / tidal)
• Land which is included within the EA’s Flood Storage Areas dataset – Flood Zone 3b (fluvial / tidal)
Flood Zone 3a is defined as:
• Land within EA modelled fluvial flood risk extents predicted for up to and including 1 in 100 year return period events – Flood Zone 3a (fluvial / tidal)
• Land within EA modelled tidal flood risk extents predicted for up to and including 1 in 200 year return period events – Flood Zone 3a (fluvial / tidal)
• Land within EA modelled surface water flood risk extents predicted for up to and including 1 in 100 year return period events – Flood Zone 3a (surface water)
Flood Zone 3a has been split into ‘(fluvial / tidal)’ and ‘(surface water)’ within the Web Map, and the above definition explains which datasets have been used for each. Flood Zone 3a may exceed EA’s Flood Map for Planning’s Flood Zone 3 in some locations. This is due to differences in the modelling methodologies used to define fluvial and surface water flood risk mapped extents. It is for this reason why Flood Zone 3 does not equal Flood Zones 3a plus 3b.
Where Flood Zone 3a exceeds Flood Zone 3, Flood Zone 3a as defined by this document takes precedence and should be applied accordingly. It should also be noted that, Flood Zone 3a always includes land also defined as Flood Zone 3b. This is no different from how Flood Zone 2 incorporates land within Flood Zone 3. Sites within Flood Zone 3a and / or 3b as defined by this SFRA will be treated as if it were in Flood Zone 3 with regards to the needs of the NPPF, PPG and site-specific FRA submission requirements. Where a location is mapped to be within two or more Flood Zones, the requirements for the highest risk zone must be applied.
In line with nationally defined responsibilities for management of flood risk, applications will be assessed by the organisations defined as follows:
- Flood Zone 3a / 3b (fluvial / tidal): Environment Agency and for minor developments Local Planning Authority applying relevant Standing Advice
- Flood Zone 3a (surface water): Local Planning Authority only
This approach is consistent with existing statutory requirements and means that there is no change to the permitted development rights and policy requirements listed within the Town and Country Planning (General Permitted Development) (England) Order 2015 as these only relate to the EA’s Flood Zones 1, 2 and 3. For this reason, site-specific FRAs are still required for developments requiring prior approval (in relation to change of use permitted development rights) if located within EA Flood Zones 2 or 3.
The definition of Flood Zones 3a and 3b within this SFRA cannot amend the General Permitted Development policies without the adoption of an Article 4 Direction. Article 4 Directions are detailed on each Borough’s respective website and should be reviewed by applicants to ensure all requirements are met.