Flood Consequence Assessment (FCA) for Planning in Wales

A flood consequence assessment is the site-specific report that a development in Wales needs when its land is shown at risk of flooding or coastal erosion. It is the Welsh planning system's equivalent of the English flood risk assessment, prepared to the standards set out in Technical Advice Note 15 (TAN15) and Planning Policy Wales, and it is the evidence Natural Resources Wales looks for before it will support a scheme. Its job is to show that the consequences of flooding on the site can be understood and managed safely for the lifetime of the development, and that the proposal will not make flooding worse anywhere else.

Unda has prepared more than 5,000 flood risk assessments and flood consequence assessments since 2014, across England and Wales, working with developers, architects and planning consultants. Our chartered flood risk consultants know how Natural Resources Wales reviews an application in practice, so the report is built to answer the questions the reviewer will actually ask.

A flood consequence assessment does not exist to stop development on flood-risk land. It exists to prove the flooding can be lived with, and to unlock a planning decision that would otherwise stall.

What is a flood consequence assessment?

A flood consequence assessment (FCA) is a technical report that examines the sources, probability and depth of flooding at a proposed development site in Wales, judges the consequences for the people and property that would occupy it, and sets out the measures needed to keep them safe over the development's design life. It is required under TAN15 and forms part of the planning evidence Natural Resources Wales assesses.

The name matters. In England the same exercise is called a flood risk assessment; in Wales it is a flood consequence assessment, because Welsh policy puts the emphasis on the consequences of a flood that reaches the site rather than on probability alone. The distinction is more than a label. A site can sit behind defences, or be shown as low probability on a national map, and still need an FCA because TAN15 asks what happens when water does arrive.

Flood consequence assessment or flood risk assessment: which do you need?

The single most common question we field from developers working across the border is which report their site needs. The answer follows the country the site is in and the policy that governs it, not the wording a planning officer happened to use. The table below sets out the practical differences.

If your site is in England, you need our flood risk assessment for planning instead, and possibly a Sequential or Exception Test. For the policy background on each system, our guides to TAN15 in Wales and the NPPF in England explain when each report is triggered.

Is this the right assessment for your site?

Flood work comes in several forms, and the wrong one wastes time at validation. Use this quick router to land on the right service, then talk to us if your site sits across more than one.

• Your site is in Wales and flood risk is flagged. A flood consequence assessment is the report you need, and you are on the right page.
• Your site is in England. You need a flood risk assessment for planning, not an FCA.
• You have been asked to justify the location. That is a Sequential or Exception Test, which can sit alongside an FCA or FRA.
• The national map looks wrong for your site. Bespoke hydraulic flood modelling can refine or challenge the mapped extent.
• Groundwater, springs or a basement are the concern. A groundwater flood risk assessment treats the source the national maps miss.
• You are chasing BREEAM credits. A BREEAM flood risk assessment is structured for the Pol 03 credit.
• Not sure which applies? Contact us with the site address and we will point you to the right report before you commit to anything.

When does a site in Wales need a flood consequence assessment?

The starting point is the Flood Map for Planning published by Natural Resources Wales, which replaced the old Development Advice Map in December 2021 and now carries the TAN15 Defended Zones layer. If your site falls within a mapped flood zone, or behind defences, or where surface water and small watercourses are shown, TAN15 is likely to require an FCA. In 2024-25 alone, NRW responded to around 2,100 planning consultations where a local authority had flagged flood risk as a constraint, so the requirement is far from rare.

• Flood Zone 2 or 3. The site is mapped at moderate or high probability of river, sea or surface water flooding on the Flood Map for Planning.
• A TAN15 Defended Zone. The land sits behind defences meeting the 1-in-100 (river) or 1-in-200 (tidal) standard; development is allowed but the residual risk of overtopping or breach must be assessed, and an FCA is required regardless of the defences.
• A vulnerable land use. Housing, schools, hospitals and emergency services are classed as highly vulnerable and face the tightest tests.
• Surface water or a small watercourse. The 2025 map added these layers, and lower-risk zones next to a small watercourse can now trigger an assessment.
• Potential to change flooding elsewhere. Development that could raise flood levels or divert flow on or around the site needs its consequences assessed.

The flow below is the quick version of that logic. It is a screening guide, not a substitute for advice: the safest first step is always to check the site and confirm the requirement with us or the local planning authority.

What changed under the 2025 TAN15

Anyone relying on older guidance, or an older consultant's report, is working to a policy that no longer applies. The revised TAN15 took effect for all planning applications made on or after 31 March 2025, replacing the 2004 TAN15 and the 1998 TAN14. It is the biggest change to Welsh flood planning policy in over two decades, and it reshapes when an FCA is needed and what it must contain. Applications made before that date are still assessed under the old TAN15.

1. The Flood Map for Planning is now central. The digital, twice-yearly map (updated in May and November) sits at the heart of the assessment, with new layers for surface water, small watercourses and coastal erosion.
2. Defended Zones are recognised. Areas behind defences meeting the 1-in-100 river or 1-in-200 tidal standard are mapped as Defended Zones, where development is allowed but residual risk must be shown to be managed.
3. FCAs are mandatory across a wider range of applications. More schemes now need one, and each must address breach, blockage, exceedance and climate change, not just present-day flood levels.
4. Coastal erosion is in planning policy for the first time. Proposals in erosion-prone areas must align with the relevant Shoreline Management Plan.
5. A new Notification Direction applies to greenfield sites. Local authorities must notify Welsh Ministers of highly vulnerable development on previously undeveloped Flood Zone 3 land, which opens a call-in window.

No competitor page we have seen yet reflects the 2025 TAN15 in full. Building your evidence on the current policy, not the 2004 version, is the difference between a report NRW accepts and one it sends back.

We keep our own commentary current as the policy beds in. For the detail, see our explainers on the new TAN15 as a policy U-turn, TAN15 explained, the role of Natural Resources Wales in flood risk planning, and the Flood Map for Planning Wales flood zones.

What a flood consequence assessment covers

An FCA is a proportionate document. A straightforward site behind good data needs a desk study; a complex coastal or fluvial site may need hydraulic modelling. Whatever the scale, a compliant assessment works through the same core questions.

Sources and probability of flooding

We identify every relevant source, which under the 2025 map means river, sea, surface water and small watercourses, and set out the probability of each reaching the site. Our guide to the sources of flood risk explains why more than one usually matters.

Flood levels, depths and climate change

We establish design flood levels for the site and apply the climate change allowances TAN15 requires, so the assessment holds for the development's lifetime rather than today's conditions. Our note on climate change allowances for planning covers the principle that applies on both sides of the border.

Finished floor levels and flood resilience

Where the consequences need managing, we set finished floor levels above the design flood level and specify resilient construction, flood-compatible materials and, where appropriate, sustainable drainage. Resilience by design is now an explicit expectation of the 2025 policy.

Safe access and egress

The assessment shows that people can enter and leave the site safely during a flood, or shelter in place where that is the safer option. This is often the point on which NRW's view of a scheme turns.

Residual risk behind defences

For a Defended Zone, we assess what happens if a defence is overtopped or breached, because the defence reduces risk but does not remove it. Our explainer on residual flood risk sets out why this matters.

Off-site and neighbouring impact

Finally, we check that the development will not raise flood levels or divert flow onto neighbouring land, which is a core acceptability requirement and a frequent reason for objection when it is left out.

The report you receive

The deliverable is a standalone report written for the reviewer, not a data dump. It draws its conclusions clearly and gives the planning case for the scheme.

• A clear risk conclusion. The flood risk to the site, from every relevant source, stated plainly.
• The consequences assessed. Depths, levels and hazard for the proposed use over its design life, including the climate change allowance.
• Mitigation set out. Finished floor levels, resilience measures, safe access and egress and, where relevant, drainage.
• Policy compliance demonstrated. How the scheme meets the TAN15 justification test and acceptability criteria.
• NRW-ready. Structured to answer the questions Natural Resources Wales asks, so review is quicker and objections are less likely.

Turnaround is typically 5 to 10 working days for a straightforward desktop site once we have the information we need, and longer where hydraulic modelling or complex coastal or fluvial risk is involved. We confirm a timescale with every quote.

What does a flood consequence assessment cost?

There is no flat fee, because no two sites carry the same risk. What drives the price is the work the site actually needs, not a fixed tariff.

• The flood sources in play. A single river source is simpler than a combined river, tidal and surface water picture.
• Whether modelling is needed. A desk study costs less than a site that needs bespoke hydraulic modelling to establish design levels.
• Site size and the proposed use. A larger or more vulnerable development carries more assessment.
• Data availability. Where NRW modelled levels already exist, we can move faster than where new data must be derived.
• Defended or coastal sites. Residual risk and coastal erosion add work the 2025 policy now expects to see.

Every quote is tailored to the site and free. Tell us the location and the proposal and we will scope it properly rather than quote blind.

Welsh flood risk planning policy in context

An FCA does not sit on its own. It is the technical evidence that carries a scheme through a policy framework made up of several parts, and understanding how they fit together is part of getting the report right.

• Planning Policy Wales sets the national planning framework, with flooding handled through TAN15 and its justification test and acceptability criteria.
• Future Wales: the National Plan 2040 sets the national development strategy that local development plans must follow.
• Natural Resources Wales is the statutory consultee on flood risk, maintaining the Flood Map for Planning and advising local authorities, though it does not itself grant or refuse permission.
• Local planning authorities make the decision, weighing NRW's advice and the FCA alongside the rest of the application.

Wales is also investing heavily in flood management, with £85 million allocated for 2026-27, its highest annual figure, including a £291 million, five-year Coastal Risk Management Programme covering 15 schemes. We cover this in our piece on Wales' £85m flood investment. New defences reduce the likelihood of flooding, but they do not remove the planning requirement, which is exactly why Defended Zones still need an FCA. For the broader policy picture, see the Welsh Government's planning policy and guidance on flooding.

Why choose Unda for your flood consequence assessment

We are flood risk specialists, not a general engineering practice that also does flood work. That focus is what makes the report land.

• Over 5,000 assessments since 2014. Deep experience of what does and does not satisfy a reviewer, across England and Wales.
• Current on the 2025 TAN15. Defended Zones, coastal erosion and the Notification Direction are built into how we scope every Welsh site.
• We know Natural Resources Wales. We understand how NRW reviews an application and write to answer it.
• Pre-application advice. We will tell you whether an FCA is even needed before you commit, and scope it honestly if it is.
• Joined-up evidence. We coordinate the FCA with Sequential and Exception Tests, flood modelling and drainage strategy so the planning evidence is consistent.

You can check a location yourself in a couple of minutes with our free flood risk map postcode checker and live river levels map before you get in touch. For local context, our flood risk work is organised by area, by river and by local authority.

How it works

1. Tell us about the site. Send the location and the proposed development and we will confirm whether an FCA is needed.
2. We scope and quote. A tailored, no-obligation quote within 60 minutes on a working day, with a timescale.
3. We assess the risk. Desk study or hydraulic modelling as the site demands, working from NRW data and the Flood Map for Planning.
4. We design the mitigation. Finished floor levels, resilience, safe access and egress, and residual-risk measures where defences are involved.
5. You receive an NRW-ready report. A clear, policy-compliant FCA to submit with your application.

Flood consequence assessment: frequently asked questions

Get your flood consequence assessment underway

If your Welsh site is flagged for flood risk, the FCA is usually the report standing between you and a planning decision. Getting it right first time, on the current 2025 policy, is the fastest route through NRW review.

Prefer to talk it through? Contact our experienced flood risk consultants on +44 (0) 1293 214444 or email enquiries@unda.co.uk, and we will point you to the right report for your site.