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.