New flood maps for Wales – National Flood Hazard and Risk Maps

For the first in our series of three blogs about the new flood maps for Wales, George Baker, Associate Director looks at the National Flood Hazard and Risk Maps for Wales.

Our flood risk modelling capabilities continue to move on in leaps and bounds. This has allowed the development of a whole new suite of flood maps for Wales, replacing the predecessor maps with some of the most detailed national flood mapping products available in the UK and internationally.

Each is aimed at specific users – from the public looking to check if they are at risk, to planners and insurers concerned about future development and climate change.

Since the formation of Natural Resources Wales (NRW) in 2013, there has been considerable investment and innovation in the creation of new systems and products that better address the needs of Wales and an increasing divergence from approaches in England. Other drivers for change include the EU Floods Directive that has required the publication of national flood hazard information and forthcoming changes to planning policy for development and flood risk (TAN15).

As a result, for the first time in years we are seeing many new and changing flood maps, and we know from our discussions with clients that many are struggling to keep up with the pace of change.

This article has been prepared as a three-part series, to provide an introduction to the new maps and a useful reference for those that only infrequently need make use of the maps:

Part 1 – National Flood Hazard and Risk Maps

Part 2 – Flood Risk Assessment Wales

Part 3 – Flood Map for Planning

National Flood Hazard and Risk Map

In July 2020, Natural Resources Wales released the National Flood Hazard and Risk map as part of their duties under the Flood Risk Regulations (2009) and the EU Directive (2007/60/EC). This map contains information on the frequency, extent, depths, velocities and hazard of flooding for fluvial, tidal and surface water risks. The modelling for this was undertaken by JBA for all of Wales consistently applying the same methodology, data and technology. These are the most detailed national flood mapping products in the UK and for the first time include explicit modelling of culverts and bridges, whole catchment rainfall models, and a consistent 2m high-resolution model resolution.

All Lead Local Flood Authorities (LLFA’s) were involved in the production of the these new maps. Firstly, by providing key asset information to NRW for incorporation into the flood models. Secondly, through an innovative model review portal LLFA’s could review and comment on draft model results, flagging areas for improvement and imparting their local knowledge to a national flood risk mapping exercise.

How to use these new maps

The resulting maps are really useful but remember, they are based on national scale modelling and therefore make various broad assumptions and simplifications in the modelling. More detailed local models are not included and at this stage the climate change scenarios have not yet been published.

The ‘risk’ component of the maps provides a nationally consistent understanding of the effects of flooding on people, economy and environment. These metrics were calculated for 2,207 communities across Wales and were calculated using a new Economic Toolset development by JBA. The data now informs a new Communities at Risk Register (CaRR) that together with the National Strategy for Flood and Coastal Erosion Risk Management in Wales guides future investment in flood risk management across Wales.

The National Flood Hazard and Risk maps have no official status for planning or insurance. They are also presently a little difficult to navigate through NRW’s website, however all the data can be downloaded in a range of GIS formats for the Lle GeoPortal.

For the flood risk professional they are a treasure trove of information, although for most people it may be best to give this map a miss. This is because these maps were not really produced for widespread public consumption, but to satisfy an EU directive.

Want to know more?

To understand how Welsh Government want the public to learn about and understand flood risk, please come back soon to read Part 2 of this blog series on Flood Risk Assessment Wales (FRAW).

You can also email George Baker for more information about the National Flood Hazard and Risk Maps for Wales.

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