“The council are asking me to do a Flood Risk Assessment, but my property/development is in a flood Zone 1…”

It’s a common query we deal with amongst planners and architects, and one that can cause unnecessary stress, particularly if you’re not prepared.

Historically, your flood risk Zone would have been the main decider as to whether you needed a Flood Risk Assessment (FRA) or not. So, it’s understandable to assume that this is still the case.

However, legislation has changed in recent years, and although we previously had to assess the flood risk from all sources for sites in flood zone 1, we are now having to provide flood risk assessment reports for site that have been highlighted by the LPA as being at risk from other sources rather than Fluvial or Tidal.

In this post, we uncover the reasons why the council are asking you for an FRA when your property or development is in a Flood Zone 1.

Read on to find out more…

Your Drainage Infrastructure Could Be To Blame

If your site is of 1 hectare or more and you’re in a Flood Zone 1, then a FRA is mandatory. However, smaller sites in a Flood Zone 1 may require a Flood Risk Assessment, particularly if you’re in an area that’s been highlighted by the Environment Agency as having a critical drainage problem.

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What Does ‘Critical Drainage Problem’ Mean?

Critical Drainage Areas (CDA) are specific areas in a Flood Zone 1 that have been identified as having a drainage infrastructure that is “at risk of failure”.

Unfortunately, much of our drainage infrastructure is ageing and in need of significant maintenance or replacement, as highlighted by a Review Of The Arrangements For Determining Responsibility For Surface Water And Drainage Assets, 2020.

New developments run the risk of reducing the capacity of the land to provide natural drainage, and this increases the risk of surface water runoff.

So, even if your site/development is not in an area where flooding problems generally occur, the ageing drainage infrastructure in the vicinity of the site which dos not have the capacity to deal with extreme rainfall events due to climate change, and increased urbanisation, may be the reason why a Flood Risk Assessment is required.

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Other Sources of Flooding We Assess During an FRA

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In the intro, we mentioned that we’re having to assess the flood risk from all sources. By ‘all sources’, we’re referring to things like:

  • Fluvial and Tidal (from the Rivers and the Sea)
  • Reservoirs
  • Overland Flow/Surface Water
  • Groundwater
  • Foul and surface water sewers

Sites That Are Partially Within a Flood Zone 2 or 3

If part of the Site red line planning boundary is within Zones 2 or 3, the Council and Environment Agency will request that flood model data is included in your FRA.

In other words, Flood Risk Assessments designed for sites within a Flood Zone 1 will not be suitable for a site within Zones 2 or 3.

What Flood Zone is My Site In?

If your site is in England, you can find out what Flood Zone you’re in by inputting your postcode into the Environment Agency Flood Map.

Sites located in Wales have their own Flood Zones. They are categorised as A, B and C, with areas A and B being generally low risk, whilst C represents the extreme flood outline. Zone C is divided into two zones: C1 and C2.

For those in Scotland, the Scottish Environmental Protection Agency (SEPA) determine the likelihood of flooding from rivers, surface water and coastal flooding, and it is divided into high, medium and low risk zones.

Conclusion: Purchase Your Flood Risk Assessment Today

If your site is in Flood Zone 1 and you require a Flood Risk Assessment, don’t hesitate to speak to a member of the Nimbus team. 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.