The Technical Advice Note (TAN) 15 provides essential guidance for local authorities, developers, planners and flood-risk specialists on managing development, flooding and coastal erosion in Wales.
TAN 15 has come a long way from its release in 2004, with its most recent update in March 2025 making a splash in the flood-risk and prevention sphere.
What Are the Main Changes?
- The Development Advice Map (DAM) has been retired and replaced by the Flood Map for Planning (FMfP) to aid flood risk planning decisions, placing increased emphasis on future climate change predictions.
- The Justification Test has gone through some changes and has become more scenario based and nuanced compared to more fixed version of the previous TAN 15.
- The guidelines in regards to the re-development and development of previously developed land have become more flexible. Greenfield sites are met with the strictest guidelines, where highly vulnerable development is not permitted.
- A new category has been added to the TAN 15: defended zones. This new category is reserved for areas that are maintained by Risk Management Authorities or are protected by high-quality flood defences.
- New Flood Zones for Surface Water and Small Watercourses have been added to the new TAN15, with a Flood Consequences Assessment (FCA) now being required for development located within areas in this Flood Zone.
- There is an increased emphasis on Local Development Plans (LDPs) in risk assessment and identifying flood mitigation measures. LDP sites are also granted the greatest leniency when supported by a Strategic Flood Consequences Assessment (SFCA).
- Coastal erosion risk is integrated into the planning guidance.
What Has Stayed the Same?
- The TAN 15 still contains vulnerability classifications ranging from less vulnerable to highly vulnerable, with the addition of the new ‘water compatible’ classification.
- The ‘water compatible’ classification is useful for development in areas close to bodies of water e.g. marinas and canals.
- The acceptability criteria for flooding consequences have remained relatively unchanged with the addition of climate change criteria to flood events.
- For example, the 1% flood event for rivers in highly vulnerable development will now also require assessment against climate change flood levels.
- The TAN 15 is still aimed at limiting exposure to risk for the most vulnerable in the areas of highest flood risk.
What’s Working Well?
It’s early days yet in terms of implementation of the new TAN15, however it could have the following advantages:
- Greater flexibility in re-development of previously developed land will encourage rejuvenation instead of new development on greenfield sites.
- More nuanced and plan led justification tests allows for development to no longer be forced into a ‘one size fits all’ justification system, potentially making the development process easier where supported by an SFCA.
- Clearer process for updating the Flood Map for Planning.
- Development of the new water compatible vulnerability classification, which provides clearer guidance for spaces such as marinas and open spaces.
Grey Areas – What’s Causing Confusion in the New Guidelines?
In seeking greater flexibility in approach, there is some ambiguity and some discrepancies in wording in the new TAN15 that remain to be ironed out. It is not clear which sections of the TAN relate to fluvial and surface water flooding.
- There is some ambiguity around the assessment and acceptability for the risks of surface water and small watercourses.
- Some clarification in these guidelines could go a long way to make TAN 15 more user friendly.
- Confusion surrounds the guidance on the new defended zone category and understandings on the nuances of the category, for example when discussing if defended or unprotected flood zones should be applied in certain circumstances vary. Additionally, whether ‘passive’ defences such as railway embankments can be considered as flood defences.
- There is ambiguity around what may be acceptable concerning re-development sites, which may cause confusion when trying to account for flood risk during planning.
- Definition of what would constitute ‘large’ and ‘small’ developments is unclear.
- Requirements for breach and blockage scenarios are unclear.
The Last Word
The 2025 update of TAN 15 has improved many aspects of the guidance by adding more flexibility, allowing appropriate development in areas of potential flood risk where justified in a council plan-led approach. Inevitably this does also create areas of ambiguity in the guidance that remain to be worked through and resolved by developers and regulators alike.
The Welsh Government plans to issue a Frequently Asked Questions document by the New Year, which should provide additional guidance and clarification around the implementation of the new TAN15.
WHS is looking forward to applying the new TAN 15 guidelines to projects in the future.