Flood zones 3a and 3b – Functional Flood Plains

The Department for Communities and Local Government published the “Technical Guidance to the National Planning Policy Framework” in March 2012. This is important, but not the only document relevant to consideration of flood zones 3a and 3b.

One of the key elements of discussion is the designation between flood zones 3a and 3b. It is often completely misunderstood by Local Authorities and others involved in the process.

Firstly people need to be clear as to what their role is.

  • The Environment Agency (EA) provides “flood data or modelling hydraulic information”.
  • The Local Authorities should provide a strategic flood risk assessment (SFRA) for their district or region.
  • A professional civil engineering consultant then provides an independent assessment of all of the flood risks in relation to the specific site.

There is a large difference in the quality of SFRAs across the UK. Many Local Authorities in England did not have the technical experience to produce this and most were outsourced to “lowest bidder” private consultants. There are some excellent examples, but unfortunately the low cost and quality meant many are large generic reports with limited practical detail or useful clear mapping. Many experts in hydrology agree it may have been more appropriate to have a generic report applicable to all areas in England and Wales and then then concentrate time and money on produce useful and clear maps. Which is similar to the planning process itself.

FACT: The EA does not designate what is functional floodplain or the boundary between flood zones 3a and 3b. This is the responsibility of the Local Planning Authority (LPA).

What should happen is the LPA combines its approved local plan, or settlement boundary plans and the EA mapping, to produce a detailed plan of its whole district in which a clear and unambiguous line is drawn between 1,2, 3a and 3b. As this could be critical to a development, it is important that the line is drawn along clear boundaries similar to the local plan itself. Indeed many LPAs use the same mapping background.

Some common sense is needed in drawing the line, although that is sometimes lacking in a few LPAs. They sometimes appear unable or unwilling to follow the NPPF advice that

“The identification of functional floodplain should take account of local circumstances and not be defined solely on rigid probability parameters.”

The EA mapping does not usually settlements as a relevant factor, they model land risk. Where as for a householder or developer it is clearly critical. Clearly you take considerable care when considering EA modelling information. Most flooding claims reported by the British Association for Insurers are not in an area identified as at high risk by the EA.

Flood zone 3b

Zone 3b for example is defined as “land where water has to flow or be stored in times of flood”. Protecting the flood plain is absolutely critical, yet flooding should not be used to blight existing settlements.  Existing settlements should never be shown within 3b.

The only types of existing development which can be shown within 3b are water compatible or essential infrastructures.

It is very rare for development to be permitted in 3b. EA evidence shows that that development in England on genuine flood plain zone 3b is minimal. In the Engineering community there is some concern that the EA may deliberately try to suggest more development takes place (then their own evidence proves) to shift focus away from their flood management role.

Flood zones 3a and 3b

For example, an infill development within an existing settlement at high flood risk would be 3a, but outside the development boundary the land would be 3b.The aim is to protect the land around existing settlements such that they may continue to act as flood plains, not try and blight local communities.

Some LPAs may suggest that the “take a conservative approach” and refuse development on the basis that it is in a location which may flood. However, that is not their role. There are lots of relevant environmental factors to consider at a location. Surveys show that the public would choose a house with some localised external flooding on a once a year basis, over being located next to a main road, with 24 hour traffic pollution and noise.

LPAs should not ignore, or put their own spin on the Government advice, they should to follow it. In the end, they risk an appeal, which on failing to follow the advice they may well lose, wasting our tax payer’s money.

Every site is different, but experience is always critical. The above information does not constitute professional advice and opinions may vary between Engineers.

flood zones 3a and 3b