Technical Advice Note (TAN) 15 guides planners, developers, local authorities and flood-risk specialists on development, flooding and coastal erosion in Wales. An update was released on October 2019.

Technical Advice Notes (TANs) have been released by the Welsh government to guide planning since 1996. TAN 15 was first released in 2004.

The guidance in TAN 15 contains essentials to inform decision making, such as:

• development vulnerability categories
• definition of flood zones
• flooding acceptability criteria
• justification test details.

Why is TAN 15 important?

Flooding occurs relatively infrequently in Wales, but it can have a significant impact upon people’s livelihoods. When severe, it can pose a danger to life.

Approximately 12% of the housing stock in Wales is thought to be at some level of risk from flooding, whether that be from rainwater, rivers, or the sea.

Research into the effects of climate change on rainfall intensity, river flows and sea levels suggests that the probability of flooding is going to increase in the future.

Coupled with this, the increasing demands for housing and other types of development due to population increase make it vital that future development is carefully planned to prevent flood risk increasing.

Time for an update

The updated TAN 15 has removed the Development Advice Map (DAM) and replaced it with an integrated central flood map, including:

• areas benefitting from flood defences
• surface-water flooding
• flooding from Ordinary watercourses such as ditches, brooks and reens
• flooding due to climate change, using the central estimate.

The flood zone definition is as follows:

Flood Zone 1 (Very low risk)
Less than 1 in 1000 (0.1%) chance of flooding in a given year.

Flood Zone 2 (Low risk)
Less than 1 in 100 (1%) but greater than 1 in 1000 (0.1%) chance of flooding in a given year, including climate change.

Flood Zone 3 (Medium and high risk)
A greater than 1 in 100 (1%) chance of flooding in a given year, including climate change.

Other key changes in the proposed update to TAN15 include:

• Changes to development categories, including a new ‘water-compatible development’ category. Land uses such as renewable energy have been added and some development types have changed categories.
• Emphasis on the importance of the Development Plan and the need for comprehensive Strategic Flood Consequences Assessments (SFCAs) to inform development strategies, site selection and planning policies.
• Guidance on how major regeneration initiatives affecting communities located in areas of flood risk should progress through national and regional levels of the planning system.
• Integration of TAN 14 guidance on coastal erosion with TAN 15. This will enable TAN 14 to be cancelled.
• Updated guidance on the justification and acceptability tests making it clear that planning authorities should not consider proposals for highly vulnerable development in high and medium risk areas (Flood Zone 3).
• New advice on flood-resilient development and on considerations when proposing new or improved flood defences.
• Residential development in Flood Zone 2 is no longer ruled out in the national planning policy (Zone C2 in DAM maps). This is subject to acceptability criteria being satisfied, which are clarified in Section 11 of the document.
• The design event from which developments should be flood free, is more clearly tabulated in Section 11. Climate change has also now been included in the table, with the design event remaining the same for all types of development except emergency services, which require more conservative design (they must be flood free in a 1000-year event).
• The tolerable conditions during an extreme event have been amended in terms of site-specific FCAs. The rate of rise and speed of onset variables have been removed, with the focus remaining on flood depths and velocities.
• A flood hazard matrix is also presented in Section 11, linking the hazard values to a “hazard to people” classification, which is useful to use when looking at emergency access/egress.
• The technical requirements of an FCA are clarified in Section 12, listing key items, including:
• a plan showing existing and proposed site levels
• an assessment of all sources of potential flooding such as surface and ground water, rivers and the sea
• peak flood depths, velocities and duration of flooding
• a plan showing access/egress arrangements
• an assessment of flood storage volumes displaced by a proposed site.

The last word

The updated TAN 15 is available on the Welsh Government website for public consultation. Comments must be submitted by 17 January 2020, using an online form, email and post.

We will soon be submitting our comments. Get on board too!