Flood Consequence Assessments for Wales

Flood Consequence Assessments TAN15 and PPW - it can be confusing, but we're here to help.

Professionally written, comprehensive flood consequence assessments, aligned to all Welsh planning policies by chartered subject matter experts.

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Aegaea are experts in flood consequence assessments, surface water drainage strategies and flood modelling suitable for all applications in Wales

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A flood consequence assessment is a requirement in Wales for developing in a flood risk area. It is analogous to a Flood Risk Assessment in England, but uses slightly different criteria for approval as it falls under Planning Policy Wales (PPW), rather than NPPF.

We’ve worked on thousands of flood risk assessments. While the policy isn’t unique, we know that every development is. It’s your development, its personal, and it needs an expert that understands the nuance and details that make a successful FCA for planning.

Every quote from Aegaea is free, unique and bespoke to your requirements, it’s just one of the ways that we set ourselves apart.

​Our expert consultants take the time to understand what you need and when you need it – delivering high quality, professional reports that have helped hundreds of customers obtain planning permission – all reviewed and signed off by Chartered professionals from CIWEM.

From a kitchen extension in Cardiff, to hydropower schemes, to new build developments, experience the difference of working with Aegaea and drop an email, form or call to our experts.

Scroll down to find out more about our service, our experts, find out more about FCAs, read our frequently asked questions, send us an enquiry, or submit your drawings and files.

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Leading Flood Risk Experts from Aegaea

Nick Darling-Drewett
Principal Flood Risk Consultant
I’m a Principal Flood Risk Consultant at Aegaea with extensive experience in producing FRAs and drainage strategies. Specialist Subject: FRAs
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Oliver Harvey
Senior Flood Risk Consultant
I am a Senior Flood Risk Consultant at Aegaea with extensive experience in supporting developers and clients by providing flood risk and SuDS reports to ensure they achieve their aspirations for...
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Jack Allen
Flood Risk and Drainage Consultant
I am a Flood Risk and Drainage Consultant, with a BSc in Geography and a MSc in Water, Energy and the Environment. I have experience in writing flood risk assessments for both major and minor...
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Frequently Asked Questions

A Flood Consequence Assessment (abbreviated to FCA) is a planning document that allows clients and local authorities to assess the flood risk to a site. This allows local authorities to understand whether a development will be safe to build in its current state in relation to different types of flooding. The FCA will need to demonstrate compliance with the relevant national (Planning Policy Wales and TAN15) and local policy.

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, and includes advice on:

  • using development advice maps to determine flood risk
  • assessing the flooding consequences of proposed development
  • using development plans and development control to mitigate flood risk

In general, a Flood Consequence Assessment will be required for any development within an area at risk of flooding. Areas at risk of flooding are defined by TAN15 and Natural Resources Wales (NRW) which publish a number of maps, such as the Development Advice Map, to show these areas. We would always recommend checking with your Local Planning Authority if a Flood Consequence Assessment is required for your planning application.

Currently, TAN15 defines three main Advice Zones – Zone A, B and C; with Zone C divided further into Zone C1 and C2. The TAN15 Zone descriptions are provided below:

• Zone A – Considered to be at little or no risk of fluvial or tidal/coastal flooding.
• Zone B – Areas known to have been flooded in the past evidenced by sedimentary deposits.
• Zone C – Based on Environment Agency (now NRW) extreme flood outline, equal to or greater than 0.1% (river, tidal or coastal)

  • Zone C1 – Areas of the floodplain which are developed and served by significant infrastructure, including flood defences.
  • Zone C2 – Areas of the floodplain without significant flood defence infrastructure.

Under TAN15, only certain development vulnerabilities are permitted within certain Zones.

Under TAN15, the aim is to locate all new development away from Zone C and towards land in Zone A, otherwise to Zone B. All development should only be permitted in Zones C1 and C2 if it is determined by the Local Planning Authority to be justified in that location. Development will only be justified if it can be demonstrated that:

i) Its location in Zone C is necessary to assist, or be part of, a local authority regeneration initiative or a local authority strategy required to sustain an existing settlement1; or

ii) Its location in Zone C is necessary to contribute to key employment objectives supported by the local authority, and other key partners, to sustain an existing settlement or region; and

iii) It concurs with the aims of PPW and meets the definition of previously developed land; and 

iv) The potential consequences of a flooding event for the particular type of development have been considered, and in terms of the criteria contained in TAN15, found to be acceptable.

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. Typically, the 1 in 100-year event will need to be considered for areas at risk of fluvial flooding, and the 1 in 200-year event for developments in areas at risk of tidal flooding – both with appropriate allowances for climate change to determine the risk over the lifetime of the proposed development. However, in some cases there will also be a need to consider the 1 in 1000-year event both for fluvial and tidal sites. 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 design flood events, 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 1,000 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.

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Do I Need a Flood Consequence Assessment?

Ultimately you need to check with your local planning authority if you need to provide a Flood Consequence Assessment (FCA) as part of your planning application, however:

You will likely need one if you are

  • developing in or near a flood zone,
  • to support an application for a flood risk activity permit,
  • projects/schemes located in areas at risk of flooding (including surface water)

The FCA has to be carried out by a suitably qualified person such as a flood management consultant and must demonstrate:

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

Alternatively, you can speak to one of our experts and we can do all that for you! We have worked across Wales on behalf of private developers, Schools, Power Generation schemes and local authorities, we’re well placed to help.

What are the Welsh Flood Zones?

Instead of flood zone 1, 2 and 3 in England, Wales adopts the following flood zones:

  • Flood Zone A – the lowest risk zone for Wales. Justification test is not applicable, no need to consider flood risk, although drainage may still be required.

  • Flood Zone B – Within the precautionary approach, developments within Zone B must adhere to the practice of applying finished floor and site levels to higher than the adjacent extreme flood outline.

  • Flood Zone C – Developments within this zone must take flood control and flood issues at the heart of a development application

  • Flood Zone C1 – Within C1 development can take place as long as the justification test and acceptability of consequences can be proven.

  • Flood Zone C2 – should only allow development within it that is less vulnerable and that also meets the justification test and the acceptability of consequences. Highly vulnerable development and emergency services should not be allowed.

These zones are defined in Technical Advice Note 15 (TAN15) and are part of Welsh planning policy.

What is TAN15?

TAN15 is the advisory note relating to development and Flood Risk and forms part of Planning Policy Wales.  It is one of a number of TAN documents relating to requirements for developers. The aim of PPW and TAN15 is:

“The general approach of PPW, supported by the TAN, is to advise caution in respect of new development in areas at high risk of flooding by setting out a precautionary framework to guide planning decisions.

The overarching aim of the precautionary framework is, in order of preference, to

  • Direct new development away from those areas which are at high risk of flooding.

  • Where development has to be considered in high risk areas (zone C) only those developments which can be justified on the basis of the tests outlined in section 6 and section 7 are located within such areas.”

TAN15 also sets out the exact requirements for the justification test and the acceptability of consequences assessment.  These are generally more prescriptive and restrictive to their counterpart policies in England.

The Justification Test

There are four justification criteria and in order to pass the Justification test, you must meet ALL four of the criteria.

The development should be located only in an area of flood risk which is developed and served by significant infrastructure, including flood defences (Zone C1 of the DAM)

Its location is necessary to assist a local authority regeneration initiative or strategy , or contribute to key employment objectives, necessary to sustain an existing settlement or region

The site meets the definition of previously developed land (i.e. it is not a Greenfield site) and concurs with the aims of Planning Policy Wales (i.e. the presumption in favour of sustainable development).

A Flood Consequence Assessment has been produced to demonstrate that the potential consequences of a flood event up to the extreme flood event (1 in 1000 chance of occurring in any year) have been considered and meet the criteria below in order to be considered acceptable.

The Acceptability of Consequences

What are the acceptability of consequences and how do they inform decision making?

  • Flood defences must be shown by the developer to be structurally adequate particularly under extreme overtopping conditions (i.e. that flood with a 1 in 1000 chance of occurring in any year).

  • The cost of future maintenance for all new/approved flood mitigation measures, including defences must be accepted by the developer and agreed with the Environment Agency (now Natural Resources Wales).

  • The developer must ensure that future occupiers of the development are aware of the flooding risks and consequences.

  • Effective flood warnings are provided at the site.

  • Escape/evacuation routes are shown by the developer to be operational under all conditions.

  • Flood emergency plans and procedures produced by the developer must be in place.

  • The development is designed by the developer to allow the occupier the facility for rapid movement of goods/possessions to areas away from floodwaters.

  • Development is designed to minimise structural damage during a flooding event and is flood proofed to enable it to be returned to its prime use quickly in the aftermath of the flood.

  • No flooding elsewhere.

  • Developer is required to demonstrate that the site is designed to be flood free for the lifetime (A1.5) of development for either a 1 in 100 chance (fluvial) flood event, or a 1 in 200 chance (tidal) flood event including an allowance for climate change (depending on the type of flood risk present) in accordance with table A1.14.

  • In respect of the residual risk to the development it should be designed so that over its lifetime (A1.5 of TAN15) in an extreme (1 in 1000 chance) event there would be less than 600mm of water on access roads and within properties, the velocity of any water flowing across the development would be less than 0.3 m/second on access roads and 0.15m/second in properties, and the maximum rate of rise of floodwater would not exceed 0.1m/hour. (see table A1.15 of TAN15).

The acceptability of consequences criteria are highly detailed and usually will require flood modelling in order to prove that they have been met.  It is therefore always sensible to engage with NRW and the local authorities early to ensure that their requirements in terms of scale of assessment are understood clearly. They also vary by vulnerability of asset – contact us for more.

Related Content

Read more related services and news updates surrounding Flood Consequence Assessments and Wales

Minor Development
Major Development
Flood Response Evacuation Plan (FREP)
Updates to the NPPF, Chapter 14 – Flood Risk, 20th July 2021
Flood Risk Assessment for Agricultural Land
Commercial / Industrial Flood Risk Assessment
Flood Risk Assessment for Essential Infrastructure

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