Challenging our flood maps

How to challenge our flood maps

If you want to challenge our flood maps, you must send us:

  • your new flood risk model
  • a flood risk model report and relevant maps
  • a flood map change note (contact the local Flood Risk Analysis team on the email addresses below for more information)

You must provide flood risk evidence that improves on the evidence we hold.

Make sure you include the information we need by using our:

Contact the local Flood Risk Analysis team before your start your challenge. The team will discuss the approach you need to take and the level of modelling we’ll need:

FRASouth@cyfoethnaturiolcymru.gov.uk
FRANorth@cyfoethnaturiolcymru.gov.uk

Challenges will inform updates to our Flood Risk Assessment Wales map and the Flood Map for Planning.

Our flood risk models and maps

Our flood maps use detailed mathematical models to interpret the best available data about the landscape and water flows.

We’ve considerably improved the quality and accuracy of our modelling and mapping over time. However, we acknowledge there may be areas where we could improve or update our flood risk information.  

The data we use comes with uncertainty due to limits of accuracy in our measurement and modelling methods.

What you can challenge in our flood risk maps

Flood Risk Assessment Wales Map

You can challenge the following layers in the Flood Risk Assessment Wales map

  • rivers
  • the sea
  • small watercourses and surface water
  • defended areas

This map shows the areas benefitting from flood defences with a standard of protection against flooding from rivers or the sea equal to or greater than 1 in 30 chance of flooding in any given year.

Areas can benefit from flood defences even if the defence is overtopped because they may stop flooding if the presence of that defence means the flood water does not extend as far as it would if the defence were not there.

Find out more about the Flood Risk Assessment Wales map and the high, medium, low and very low risk categories.

Flood Map for Planning

You can challenge the following layers in the Flood Map for Planning

  • Flood Zone 3 – for rivers and surface water, greater than or equal to 1 in 100 chance of flooding in any given year, including the effects of climate change; 1 in 200 chance of flooding for the sea
  • Flood Zone 2 - for rivers and surface water, between 1 in 100 and 1 in 1000 chance of flooding, including the effects of climate change; between 1 in 200 and 1 in 1000 chance of flooding for the sea
  • TAN15 defended zones

TAN15 defended zones shows areas of land that benefit from formal flood defences that are owned and maintained by Risk Management Authorities.

Flood defences built before 1 January 2016 have the following level of protection:

  • 1 in 100 chance of happening in any given year for rivers
  • 1 in 200 year chance of happening in any given year for the sea

Flood defences built after 1 January 2016 must meet the previous level of protection but also include:

  • an allowance for a design freeboard (an added allowance for defence height to cover uncertainty in the modelling)
  • an allowance for the effects of climate change (over a 100 year development lifetime)

Using local flood risk models

For most of Wales, we use a ‘generalised model’ for flood risk from rivers and the sea. But in areas with a high risk to people, for example urban areas, we use detailed local flood risk models.  

You should use these detailed local flood risk models as the basis of your new models, where these are available. You can see the location of these models on our Flood Map for Planning, as the ‘NRW Local Model Manager’ layer in the ‘Detailed map’.

You’ll have to request the data for these local models and we may charge you for this service datadistribution@naturalresourcewales.gov.uk

For some areas, we won’t have any suitable data and you’ll need a new model.  

What happens after you challenge our flood maps?

Our local Flood Risk Analysis team will:

  • evaluate your flood model report
  • test your flood model and the hydrology to understand your results and how you developed the model
  • check the stability of your model
  • compare your results with our own information

In some cases, we may not have the necessary software to do a detailed assessment of your model. In this case, we’ll send your model to a third-party consultant for an independent peer review.

If your challenge is successful

If your challenge to our flood maps is successful, this means your model is suitable to change our flood maps.

This does not mean that:

  • we agree that your model is fit for all purposes
  • your development proposals are appropriate
  • we will make no further comment on flood risk in the area you have challenged

You also need to consider:

  • flood risk cannot be eliminated and is expected to increase over time because of climate change
  • the public can ask to see the results of our assessment of your model under Freedom of Information and Environmental Information Regulations
  • if our assessment of your model review was part of a local authority planning proposal, the assessment will likely be available to the public as part of a planning case file
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