New TAN15 2025: Flood & Planning Policy Update

The new TAN15 took effect on 31 March 2025, and it is the largest change to flood risk planning in Wales in more than twenty years. Technical Advice Note 15: Development, Flooding and Coastal Erosion replaced an edition written in 2004, retired the Development Advice Map in favour of Natural Resources Wales's Flood Map for Planning, recognised land behind flood defences as Defended Zones for the first time, and scrapped the three-part justification test that had governed development in flood risk areas since 2004. Applications validated from that date are assessed under it; anything submitted before then stays with the old edition. Readers coming to the policy for the first time may want the plain explanation of what TAN15 is and how its flood zones work before the changes below.

The changes below are set against what they replaced, so a site previously assessed under the 2004 framework can be read across to the current one. Where a Welsh site needs one, a Flood Consequence Assessment built to the 2025 acceptability criteria is what the council and NRW will judge the proposal against.

Twenty-one years separate the two editions. The reform was consulted on three times, suspended eight days before it was due to come into force, and delayed twice more before publication.

The road to 31 March 2025

TAN15 was first published on 30 July 2004. Replacing it took three consultations, one formal suspension and two announced delays, and the shape of the final document is a direct result of that history.

The suspension is the part most often left out, and it explains the document that finally arrived. On 23 November 2021, eight days before the revised TAN15 and the Flood Map for Planning were due to take effect, Julie James MS, then Minister for Climate Change, stopped it. The statement gave the reason, and recorded that reversing the commencement would itself need legislation.

The deferred date did not hold either. In May 2023 the Welsh Government said the re-consultation had made 1 June unachievable, and that the revised TAN was unlikely to take effect before the end of that year. The version that finally emerged in 2025 is accordingly more accommodating of redevelopment than the one councils objected to. Brownfield land is treated separately from greenfield, regeneration is expressly provided for, and local planning authorities were given more room to exercise judgement.

The Flood Map for Planning replaces the Development Advice Map

The Development Advice Map that sat behind the 2004 TAN15 carries no planning status at all now: it stayed accessible for eight weeks after 31 March 2025, long enough to see the transition through, and was then withdrawn. Natural Resources Wales's Flood Map for Planning took its place, and it holds considerably more than the map it replaced.

• Rivers, sea, and combined rivers-and-sea zones. Flood Zones 2 and 3 for each, on the familiar 0.1%, 1% and 0.5% annual probability thresholds.
• Surface water and small watercourses. New, and the source of a great many assessment requirements that simply did not exist under the old map.
• TAN15 Defended Zones. Land benefiting from formal defences, mapped for the first time.
• Supporting layers. Recorded flood extents, defence locations, reservoir risk, main rivers, NRW's local hydraulic models, and Shoreline Management Plans.
• A six-monthly cycle. Republished in late May and late November each year, which means a screening result has a shelf life.

Every Welsh flood zone assumes no defences are in place and already includes roughly a century of climate change — the reverse of the English arrangement, where the base zones show present-day risk and allowances are added on top.

A team moving between the two systems has to hold both conventions at once. An identical site can screen into different zones in England and in Wales, and the reason is the map, not the river. Unda's guide to the Flood Map for Planning and the Welsh flood zones sets out the thresholds in detail, and the English climate change allowances are covered separately.

Defended Zones, and what they do not permit

A TAN15 Defended Zone is land benefiting from Risk Management Authority defences that meet a minimum standard of protection: 1 in 100 in any year for rivers, 1 in 200 for the sea. Defences built from 2016 onwards must also carry a climate change allowance and design freeboard to qualify. Older defences need not, though NRW records that they still offer a good present-day standard.

The Welsh Government's own guidance is blunt about the limit of that recognition: Defended Zones “should not be considered as a presumption for development”.

• An assessment is required regardless. Defences lower exposure; they do not remove it. The Welsh Government's FAQ states that breaches or overtopping “of even the most modern flood defences are possible”, and requires the assessment to test the standard of protection and the latest climate change allowance across the development's lifetime.
• Defended Zone status overrides the underlying flood zone for that source of flooding. Where a site is in a Defended Zone for rivers but not for the sea, Defended Zone requirements govern the river risk and ordinary Flood Zone 1, 2 or 3 requirements govern the tidal risk.
• The designation is not permanent. NRW reviews Defended Zones every two to three years against a May 2025 baseline. Where a standard of protection has fallen below the threshold, the land is reclassified as Flood Zone 2 or 3.

The map has already done exactly that. Across the three map updates since the new TAN15 came into force, a Defended Zone was modified at Bala Town and removed at Treorchy and Llwynypia in May 2025, created again at Llwynypia six months later, and modified at Mold in May 2026. Five changes in three cycles. A site screened at feasibility will not necessarily screen the same way at submission, and new defences do not automatically move a site out of a flood zone either.

The justification test is gone

The 2004 TAN15 turned on a three-part justification test. The new TAN15 retires it and puts four acceptability criteria in its place, which a Flood Consequences Assessment must satisfy in turn.

1. Flood free in the design event. The development stays free from flooding in the 1% annual probability river event or the 0.5% tidal event, with climate change applied, across its lifetime.
2. Tolerable consequences in the extreme event. In the 0.1% event with climate change, depth, velocity and hazard rating remain within the tolerable thresholds TAN15 sets for the vulnerability class.
3. No increase in risk elsewhere. The proposal does not push flooding onto neighbouring land or downstream.
4. Residual risk managed. Breach, blockage, overtopping and exceedance are assessed and designed for, not assumed away.

A report still framed around the justification test is working to a framework that has not applied in Wales since March 2025. It is the quickest single check on whether flood risk advice is current.

Flood Consequences Assessments are required more widely

Both the trigger and the standard moved. An assessment is expected where a site sits in Flood Zone 2 or 3, in a Defended Zone for any source, next to a small watercourse or caught by the new surface water layers, where the use is vulnerable, or where the proposal could change flooding elsewhere.

The content expected has moved as well. An assessment now has to address breach, blockage, exceedance and climate change projections, rather than establishing a flood level and setting a finished floor level above it. Where breach or blockage scenarios are in play, NRW should be consulted on them, and the Welsh Government describes the result as the design event in its own right — which for many sites means hydraulic modelling rather than a desk study.

Local authorities can also require an assessment on grounds the map does not cover, and the Welsh Government is explicit that the Flood Map for Planning does not map wave overtopping, historic flooding, or increased risk from blockage, overtopping and breach of defences. Residual risk therefore has to be evidenced on the site, not read off the map.

Natural Resources Wales responded to around 2,100 planning consultations in 2024-25 where a council had flagged flood risk as a potential constraint, a figure that has sat between roughly 2,100 and 2,400 a year since 2020-21.

The caseload has held steady while the evidence each application carries has grown. NRW's role stays advisory throughout: it comments as a statutory consultee, and the council decides.

Which climate change allowances apply

The climate change allowances a Welsh assessment must use were revised on 20 March 2026 and apply to applications submitted from 1 April 2026, replacing guidance issued in September 2021. TAN15 itself was not amended; the figures fed into the assessment were.

The 2080s figure also stands in for anything beyond that epoch, so a residential scheme reaching past 2125 is still tested against it. Rainfall and sea level carry their own allowances.

• Rainfall uplift. Wales-wide: 20% central and 35% upper for the 2050s, 30% central and 40% upper for the 2070s.
• Sea level rise. Given by local authority area. Cardiff, for instance, carries 0.87 m to 2100 and 1.25 m to 2130 at the 70th percentile, and 1.14 m and 1.68 m at the 95th.
• Wave and wind. Sensitivity testing at +5% on offshore wind speed and extreme wave height to 2055, rising to +10% from 2056 to 2125.
• Development lifetime. 100 years for residential development, and 75 years, which the guidance offers as a reasonable rule of thumb, for everything else.
• Which estimate to run. Strategic work generally uses central estimates. A detailed site assessment is expected to demonstrate the design event on the central estimate, the same event on the upper estimate, and the 0.1% extreme event on the central estimate.

For coastal sites the epochs matter as much as the numbers, because the 2130 horizon now sits inside the lifetime of a residential scheme consented today.

The Notification Direction

Everything above turns on how a proposal is classified. TAN15 sorts development into three vulnerability categories — highly vulnerable (housing, hospitals, schools, emergency services), less vulnerable, and water-compatible — and the Welsh Government is clear that its list is not exhaustive, so decision makers apply professional judgement to anything unlisted. England runs a parallel but separate classification under the NPPF, and the two do not map one to one.

The Town and Country Planning (Flood Risk Area Development) (Notification) (Wales) Direction 2025 accompanies the new TAN15. Where a council is minded to approve highly vulnerable development in Flood Zone 3 on land that is not previously developed, it must notify the Welsh Ministers before consent is issued. A 21-day window then opens, during which the application may be called in.

Brownfield against greenfield is the distinction that decides it. Redevelopment of previously developed land is treated more flexibly throughout the new TAN15; new highly vulnerable development on undeveloped Flood Zone 3 land is the case the Direction exists to catch.

A case from March 2026 shows both halves of this. Bannau Brycheiniog National Park Authority considered a tourism scheme at Govilon in Monmouthshire. Classified as highly vulnerable development in a flood zone, it triggered automatic referral to the Welsh Ministers and their 21-day window, with the planning officer recommending approval. The committee report also shows how far the mapping has moved — the site's risk had reduced from being entirely within a C2 flood zone to partially within Zone 2 and adjacent to Zone 3. C2 was Development Advice Map nomenclature, and it has no meaning under the current framework.

Coastal erosion enters planning policy

The 2025 TAN15 absorbs the coastal ground previously held by TAN14 (1998), which the reform cancelled, and brings coastal erosion into development planning for the first time. Proposals on the coast must align with the relevant Shoreline Management Plan for that stretch of coast, as published by NRW, and consider how the coastline is expected to move across the development's lifetime. A present-day shoreline is no longer an acceptable design assumption. Shoreline Management Plans now sit as a layer on the Flood Map for Planning alongside the flood zones themselves.

What the transitional arrangements still catch

Two flood risk policies are live in Wales at once. Applications validated before 31 March 2025, and any subsequent appeals on them, are determined under the 2004 TAN15. Long-running schemes and the appeals that follow them therefore continue on the superseded framework for as long as they run. On an older site, the first question is which edition the application sits under — the answer changes the test, the map and the evidence.

What it changes in practice

The new TAN15 is plan-led, so for councils the evidence moves upstream. Local Development Plans are expected to integrate flood mapping and strategic assessment from the earliest stages, and the Welsh Government states that an authority permitting a scheme before mitigation infrastructure is in place “will be publicly accountable for their decisions”.

• Developers and housebuilders. Site selection and pre-application work carry more weight, particularly on greenfield and coastal land, where the Notification Direction and the coastal erosion provisions can both apply.
• Consultants and engineers. The assessment is a larger piece of work: breach and blockage scenarios, an exceedance route, a stated lifetime and current allowances are now the minimum.
• Communities and landowners. Land reclassified at a map update, or newly caught by the surface water layers, may be affected without anything on the ground having changed.

Templated assessments rarely survived the old justification test. Under four acceptability criteria, each needing its own evidence, they do not survive NRW consultation at all. Unda has delivered flood risk and drainage work across England and Wales since 2014, and prepares NRW-ready Flood Consequence Assessments for Welsh planning applications, alongside wider TAN15 planning guidance and surface water drainage strategies for sites that need both. Call +44 (0) 1293 214444 or email enquiries@unda.co.uk.

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