TAN15 Wales Flood Risk Policy Updates 31 March 2025

The Welsh Government has released a long-awaited update to Technical Advice Note 15 (TAN15), changing how flood risk is assessed and managed in planning decisions across Wales. The new guidance introduces updated flood maps, revised zones and stricter policies that will significantly affect future development, particularly in areas previously considered low risk.

Key Takeaways

• Development Advice Mapping (DAM) has been discontinued with DAM references and DAM Flood Zones (C1, C2, B and A) removed
• Flood Map for Planning (FMfP) shows more land at risk of flooding in comparison to DAM
• Inclusion of a new ‘Defended’ Flood Zone and associated policies for new development within a defended area
• There have been alterations to the vulnerability classifications, including category changes
• Removal of the Justification Test (Sequential Test) in favour of defining acceptability criteria of flood consequences
• “No new highly vulnerable development will be permitted in Zone 3, regardless of the conclusions of a Flood Consequence Assessment, with the exception of proposals essential to the Development Plan Strategy”
• New development on greenfield sites at risk of flooding will face greater scrutiny and is likely to be strongly discouraged
• Redeveloping existing, previously used land in flood-prone areas might be more acceptable under specific conditions
• Greater emphasis on detailed assessment of flood depths and velocities within Flood Consequence Assessments
• Developers must now consider compensatory flood storage up to the 1 in 1,000-year event, plus climate change allowance

What is TAN15?

TAN 15 (Technical Advice Note 15) is Welsh Government policy that helps planning authorities manage development with a view to mitigating flood and coastal erosion risk. The original TAN15 was issued in July 2004, with an updated version scheduled to come into effect on December 1, 2021. However, following significant concerns, its implementation was suspended.

On 31 March 2025, the Welsh Government finally released the first update to TAN 15 since its initial publication in 2004. The new TAN came into immediate effect, fully superseding the 2004 document and applies to all new planning applications.

Development Advice Map (DAM) Discontinued

The Development Advice Map (DAM) has been discontinued and replaced with Flood Map for Planning (FMfP). DAM is to be retained on DataMap Wales for a period of 8 weeks to inform planning schemes currently being determined.

Flood Map for Planning (FMfP)

The Flood Map for Planning data shows more land at risk of flooding than the discontinued Development Advice Maps.

Flood Zone 3 displays the extent of flooding from:

• Rivers with a 1% (1 in 100) chance or greater, including climate change
• The sea with a 0.5% (1 in 200) chance or greater, including climate change
• Surface water & small watercourses with a 1% (1 in 100) chance or greater, including climate change

Flood Zone 2 displays the extent of flooding from:

• Rivers with less than 1% but greater than or equal to 0.1% (1 in 1,000), including climate change
• The sea with less than 0.5% but greater than or equal to 0.1% (1 in 1,000), including climate change
• Surface water & small watercourses with less than 1% but greater than or equal to 0.1% (1 in 1,000), including climate change

New ‘Defended’ Flood Zone

The TAN15 update includes a new Defended Flood Zone. TAN15 Defended Zones are protected by defences that shield against at least one major source of flooding. However, some areas within these zones could still be at risk from other flooding sources. Any new development within TAN 15 Defended Zones must incorporate resilience and resistance measures.

Alterations to Vulnerability Classifications

• The ‘emergency services’ category has been removed, with these uses now classified under Highly Vulnerable
• A new category has been introduced: Water Compatible
• Some land use definitions have been revised, such as public buildings (e.g. libraries), which have been reclassified from Highly Vulnerable to Less Vulnerable

Removal of the Justification Test

The old Justification Test has been replaced with a greater focus on a plan-led approach to decision-making regarding development in flood risk areas. The revised methodology prioritises a decision-making framework through a comprehensive understanding of flood risk, offering greater flexibility for redevelopment of previously developed land within flood risk areas, whilst tightening the rules for new development within the floodplain.

How Will This Affect My Development?

Zone 1: All vulnerabilities of use will be acceptable in principle provided there is no increase in flooding elsewhere.

Zone 2: Planning applications require careful consideration and must be accompanied by a FCA. Applications for new highly vulnerable development on greenfield land are only appropriate where the site has been allocated in adopted Development Plans.

Zone 3: No new highly vulnerable development on greenfield land should be permitted, regardless of the conclusion of any Flood Consequences Assessments. Water-compatible development is acceptable in all flood zones.

Defended Zones: Applications for new development on greenfield sites are not appropriate unless they are allocated in development plans. On brownfield sites, redevelopment proposals should not over-intensify use.