Flood Consequence Assessments For Wales

A Flood Consequence Assessment (FCA) is the Welsh equivalent of a Flood Risk Assessment. It is a planning document that shows your local planning authority what would happen to your development in a flood, how those consequences will be managed, and that flood risk will not be increased elsewhere.

It is assessed against Planning Policy Wales and Technical Advice Note 15 rather than the NPPF, alongside any local policy that applies to your site. You will usually need one for development in Flood Zone 2 or 3, or in a TAN15 Defended Zone.

Planning Policy Wales (PPW) is the overarching national policy outlining guidance for making planning decisions in Wales. The PPW is then supported by Technical Advice Notes (TANs) which provide more detailed guidance pertaining to specific aspects or considerations of the planning process. Technical Advice Note 15 (TAN15) is the Note providing detailed guidance on development and flood risk. The current version, published in March 2025, replaces TAN15 (2004) and TAN14 (1998), and planning decisions should no longer refer to those documents. It includes advice on:

• using the Flood Map for Planning to determine flood risk
• assessing the flooding consequences of proposed development
• using development plans and development control to mitigate flood risk

A Flood Consequence Assessment is required for development in Flood Zones 2 and 3 and in TAN15 Defended Zones, and should be proportional to the nature and scale of the proposal. That includes Flood Zones 2 and 3 for surface water and small watercourses, and an FCA can also be needed outside those zones where a development could affect surface water or ordinary watercourse flows. For surface water and small watercourses, local authorities may exercise some discretion on householder applications where the risk may be lower. The starting point is the Flood Map for Planning, published by Natural Resources Wales (NRW), alongside the Flood Risk Assessment Wales (FRAW) map, which shows current risk. We would always recommend checking with your Local Planning Authority if a Flood Consequence Assessment is required for your planning application.

Wales uses Flood Zones 1, 2 and 3, split by source: flooding from rivers, from the sea, and from surface water and small watercourses. TAN15 Defended Zones are also mapped. Zones A, B, C1 and C2, which were used under the 2004 version of TAN15, no longer exist.

TAN15 sorts development into three vulnerability categories: highly vulnerable, less vulnerable and water compatible. All residential development is highly vulnerable.

The justification test in the 2004 version of TAN15 was built around Zones C1 and C2. That version has been replaced, and planning decisions should no longer refer to it.

Under the current TAN15, the fundamental principles are to restrict new development in Flood Zone 3 and to prioritise all types of development to Flood Zone 1. Whether development can go ahead turns on whether the consequences of flooding can be safely managed, including its effects on flood risk elsewhere.

There is no requirement to justify the location of householder development. For anything else, talk to us early about how the current TAN15 applies to your site.

Given the need to demonstrate the flood risks and consequences to a development, the FCA will in most cases need to include site-specific modelled flood levels for a range of return periods. TAN15 requires a range of flooding scenarios to be assessed, up to and including the event with a 0.1% (1 in 1,000) chance of occurring in any year, with an allowance for climate change. We will be able to advise you what is required for your site.

The FCA will need to assess the risk of flooding in these scenarios, and set out measures to mitigate any risks identified to comply with the requirements of TAN15 where possible

In many cases, the modelled flood level data can be obtained from Natural Resources Wales (NRW). NRW have carried out hydraulic modelling for a number of watercourses and coastal areas across Wales. Data requests can be submitted to NRW to obtain this data where available. However, in some areas, particularly more rural regions or at non-Main River locations, NRW may not have carried out this modelling work. In these situations, the onus typically falls on the developer to invest in such hydraulic modelling works to demonstrate the risks to the site and inform the mitigation measures. Aegaea can assist with these modelling works and have a separate page for this.

There are a lot of different parameters that can influence the time it takes to complete an FCA. Each project is unique and has different flood risks, designs, environmental conditions, topography, historic uses, and are subject to different planning policies. All of these can affect the time it takes for a flood risk assessment to be completed. The industry standard for an FRA is around 4 to 6 weeks, where flood modelling is available. If a hydraulic modelling exercise is required to inform the FCA this could increase the timeframes associated with the production of the report.

Our team, however, have experience in supporting over 4,100 projects and have developed methods and techniques to analyse data efficiently and effectively review every aspect in a timely manner. On average, our FCA reports take 5 to 10 working days once we have received the necessary data.

In 2019, the Welsh Government publishes Sustainable Drainage (SuDS) Statutory Guidance which set out that from 7th January 2019, all new developments of more than 1 dwelling house or where the construction area is 100m2 or more, will require sustainable drainage systems (SuDS) for surface water. The SuDS must be designed and built in accordance with Statutory SuDS Standards published by the Welsh Ministers and SuDS Schemes must be approved by the local authority acting in its SuDS Approving Body (SAB) role, before construction work begins.