All too often, information on whether or not your site is within a Flood Zone can be muddy and unclear, leaving you with more questions than you had to begin with.

Yet, this information is crucial to ensure the correct procedures are put in place during your planning applications and to avoid any refusals or delays to your application.

This post aims to clearly explain the types of flood zones, what they mean and detail the steps you can take to find out if your site is affected.

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WHAT IS A FLOOD ZONE?

Put simply, what are these elusive flood zones?

Flood zones are used by the Environment Agency as a means to indicate the probability of river and sea flooding in an area. It’s worth mentioning they do not take into consideration the presence of existing defences.

These zones were created predominantly as a tool for planning developments and do not necessarily indicate whether somewhere will or won’t flood.

Depending on which type of flood zone your development falls under, you may be subject to conducting a flood risk assessment during your planning application.

FLOOD ZONE TYPES

The Environment Agency divides these zones into three categories. However, local authorities split Zone 3 into two separate groups. More on that later.

Flood Zone 1

These zones are identified as having ‘Low Probability’ of flood risk.

Areas within Zone 1 show:

  • Less than 0.1% chance of flooding in any given year
  • The Environment Agency determine this land has a less than 1 in 1000 probable chance of river or sea flooding

“So how does this affect me and my planning applications?”

Unfortunately, whilst this most commonly means that you won’t need to carry out a Flood Risk Assessment on your site; there is a separate clause under which the Environment Agency’s classification may not cover.

Specifically, the Environment Agency’s flood zones do not account for surface water flooding or critical drainage issues within the area.

Critical Drainage Areas (CDA) are specified areas within Flood Zone 1 that have been identified as having drainage infrastructure which is at capacity and therefore cannot cope with extreme storms. These areas are at critical risk of failing during these flash floods, which may result in runoff, causing a number of potential problems.

This means that within these areas, you will still be required to carry out a Flood Risk Assessment.

Also any sites that are 10 residential units or above, or commercial sites that are above 1000m2, will require either a Flood Risk Assessment and SuDS report or a Flood Risk Assessment and Drainage Strategy report (depending on varying requirements of the Lead Local Flooding Authorities), even if the site is within a Flood zone 1

Flood Zone 2

These zones are identified as having ‘Medium Probability’ of flood risk.

Areas within Zone 2 show:

  • Between 0.1% - 1% chance of flooding from rivers in any given year (1:1000 and 1:100)
  • Between 0.1% - 0.5% chance of flooding from sea in any given year (1:1000 and 1:200)

Sites within this flood zone will be required to submit a Flood Risk Assessment during the planning application stages of development. This assessment will show the risk of flooding to the site and is a national requirement.

In order to determine the depths of flooding, we are required to obtain modelled flood levels from the Environment Agency, and it is worth noting that this information can take up to 21 days to arrive, which is something our clients are not always aware of.

A note on Flood Zone 3

These zones are identified as having ‘High Probability’ of flood risk.

Remember how earlier you were told Zone 3 is split into two groups by local authorities?

Zone 3 is actually divided into Flood Zone 3a and Flood Zone 3b. It’s worth noting that the Environment Agency do not display these distinctive zones on their Flood Maps.

Sites within Zone 3 will always be required to submit a Flood Risk Assessment during the planning application stages of development. This assessment will not only assess the risk of flooding to the site, but also identify if the site falls under 3a or 3b.

It should also be noted that any development deemed as ‘more vulnerable’, such as residential will require application of the sequential and exceptions tests also.

Flood Zone 3a

Areas within Zone 3a show:

  • 1% or greater chance of flooding from rivers (1:100)
  • 5% or greater chance of flooding from sea (1:200)

Flood Zone 3b

Also known as, Functional Floodplain.

These areas are identified as being the most at risk of flooding from rivers or sea. These zones usually show:

  • 5% chance of flooding from rivers or sea (1:20)

Often, this land is marked as an area where water has to flow or be stored in the event of a flood, therefore flood storage compensation is required in order to build in these areas. Something that clients are not always aware of either, and quite often can end up buying land in this zone, only to find that they cannot build on it. Local authorities should use their Strategic Flood Risk Assessments to identify these functional floodplains and clearly show their boundaries, in agreement with the Environment Agency.

So, how can you identify if your site is within a flood zone?

To find out if your site is within a flood zone you can visit the Environment Agency’s Flood Map for Planning.

Visit the Government's website for more information about the Government’s guidelines on Flood Zones.

If your site is within a Flood Zone and you would like to find out more about our approach to Flood Risk Assessments, speak to a member of the Nimbus team today. We’re always happy to help.

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About Nimbus Engineering

Nimbus Engineering is a dedicated team of consulting Civil Engineers with a wealth of experience in covering all aspects of Flood Risk and Drainage Design, including Sustainable Urban Drainage Systems Design (SuDS Design), Flood Risk Assessment reports (FRAs), Flood Warning and Evacuation plans (FWEPs) and Surface water management schemes, including SuDS reports,

Working with you from planning stage through to construction, as well as providing the necessary SuDS Management and Maintenance plans, you can guarantee tailored support every step of the way.

We work closely with many Local Authorities and Lead Local Flood Authorities nationwide and are therefore aware of each of their specific requirements, especially when relating to SuDS reports and Drainage strategy reports.

Sadia Luckett

Written by Sadia Luckett

Sadia Luckett is the Director at Nimbus Engineering, specialising in foul and surface water drainage & SuDS.