Before developing in an area at risk of flooding you will need to demonstrate that the flood risks and consequences can be acceptably managed in line with current national planning policy.

Check the Development Advice Map to see if the area is at risk of flooding.

Flood Consequence Assessments (FCA)

Check with your local planning authority if you need to provide a Flood Consequence Assessment (FCA) as part of your planning application.

A FCA may also be required to support an application for a flood risk activity permit, or other projects/schemes located in areas at risk of flooding.

The assessment should be used to understand the flood risks to and from the development and inform the final design and any mitigation measures required. It should be carried out by a suitably qualified person, for example a flood management consultant.

It should demonstrate:

  • the flood risks to your development
  • an assessment of the flood consequences of the development
  • the development does not increase flood risk elsewhere
  • how you will manage or mitigate against flood risk to, or caused by, your development
  • consideration of climate change in line with current government guidance

We also recommend:

  • speaking to your local planning authority before commissioning your assessment
  • reading the Technical Advice Note for development and flood risk (TAN15) for all technical requirements
  • contacting us for pre-application advice
  • speaking to your local authority for advice on flood risk from ordinary watercourses and surface water

Get more help with your FCA

Get pre-application advice from our discretionary planning advice service to:

  • provide advice on the scope of the assessment likely to be required
  • provide local knowledge, data and advice on our hydraulic models
  • discuss how to undertake an assessment when a development is located in an area of combined fluvial (river) and coastal/tidal flood risk flood risk

Preparing a flood risk model

Good practice advice on preparing a flood risk model, including what information is required and why, can be found in our guidance modelling for flood consequence assessments

If you include a flood risk model with your FCA you will also need to include a flood model checklist.

Request hydraulic modelling data

Email to find out if we hold hydraulic model data for the area you're planning to develop. Raw data is available from Lle Geo-Portal for Wales.

If the data you need already exists, we can provide the baseline model (under licence if required) and provide advice on the scope of any work that may be required to make sure it's fit for purpose and achieve the objectives of the hydraulic modelling work.

There may be a cost for this service.

Breach and blockage modelling

Your FCA should consider the possibility of flooding caused by blockages of in-channel structures (bridges, culverts, weirs etc.) and breach/failure of defences.

Read our guidance on modelling for breach and blockage scenarios.

Flood flow estimation

Request the latest guidance for estimating flood frequency (last updated December 2017). This includes recommendations on appropriate methodologies for flood frequency estimation in Wales, particularly in respect of flood risk associated with development proposals and flood hydrology calculation for flood risk mapping/modelling.

It also includes a flood model calculation template to help draft your report.

Our role in the planning process

We are statutory consultee in the planning application process.

We assess flood assessments and any other supporting documentation to decide whether you have met the requirements of Planning Policy Wales and TAN15. We also comment on the acceptability of flooding consequences and the technical soundness of the assessment.

We do not give advice on:

  • surface water flood risk and drainage
  • emergency plans
  • procedures and measures to address structural damage that may result from flooding

Read more about our role in planning and development.

Other permits and consents that may be required

You may need a flood risk activity permit, previously called flood defence consent, if you want to do work:

  • on or near a main river
  • on or near a flood defence structure
  • on or near a sea defence
  • in a flood plain

Permission is also necessary to ensure the work will not interfere with our flood risk management assets or adversely affect the local environment, fisheries or wildlife.


You may also need to obtain other licences, consents, approvals or permissions to meet other legal requirements, duties or responsibilities for conservation or protection of the environment.


You could be breaking the law if you start work without getting the necessary permits and permissions you need.

Challenging the flood map

We are updating the long term flood risk maps with data from the 2019 Flood Risk Assessment Wales (2019) project. As part of this work we will be publishing a new Flood Map for Planning in Summer 2021 to replace the existing Development Advice Map.

We cannot accept any flood map challenges until this work has been completed and a new flood map for planning has been published.  In the interim, we will continue to accept and review models submitted in support of a planning application, which will be used to inform our technical flood risk advice. However, this information will not be incorporated into the Development Advice Map at this time and there will be no change made to the flood zones.

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