- 14th December 2020
- Posted by: Miranda Pont
- Category: Blog
For the second in our three part blog series about the new flood maps for Wales, George Baker, Associate Director explores the new Flood Risk Assessment Wales (FRAW) map.
Natural Resources Wales (NRW) released the Flood Risk Assessment Wales (FRAW) map in October 2020 alongside Welsh Government’s launch of the National Strategy for Flood and Coastal Erosion Risk Management. FRAW is the new flood map for the general public who want to understand if where they live, work or visit is at flood risk.
The map is a replacement of what was previous called the ‘Flood Map’. It brings together a consistent understanding fluvial, tidal and surface water risks, information on flood defences, historic flood extents, flood warning and erosion risk. It is largely aimed at being accessible to the public, to “check if you’re at risk”.
The flood risk has been classified into three risk bands as tabulated below. The ‘Low’ risk band is loosely equivalent to Zone 2 of the previous Flood Map, while ‘Medium’ risk is equivalent to Zone 3. The high risk band is new to Wales, although similar to Zone 3b ‘functional floodplain’ that is used in England.
|Flooding from River (Annual change of flooding)||Flooding from Sea (Annual chance of flooding)||Flooding from Surface Water & Small watercourses (Annual chance of flooding)|
|High||Greater than 1 in 30 (3.3%)||Greater than 1 in 30 (3.3%)||Greater than 1 in 30 (3.3%)|
|Medium||Between 1 in 100 (1%) and 1 in 30 (3.3%) annual||Between 1 in 200 (0.5%) and 1 in 30 (3.3%) annual||Between 1 in 100 (1%) and 1 in 30 (3.3%) annual|
|Low||Between 1 in 1000 (0.1%) and 1 in 100 (1%)||Between 1 in 1000 (0.1%) and 1 in 200 (0.5%)||Between 1 in 1000 (0.1%) and 1 in 100 (1%)|
How to use these maps
FRAW uses data from detailed flood models where they are available and where there is no detailed modelling it uses the new National Flood Hazard Map (see Part 1 of the blog to learn about this map). It is therefore the amalgamation of many flood models and will be updated regularly to share best available data.
An important aspect of FRAW is that the flood risk zones describe ‘present day’ flood risk ie. no climate change allowance.
At this time the Surface Water and Small Watercourse modelling is entirely based on national scale modelling and is therefore identical to the data contain in the National Flood Hazard and Risk Map. This is useful to know if you want to see more detail, such as flood depths and velocities.
In a significant departure from the previous Flood Map, the FRAW flood zones are ‘defended’. This means that the flood map takes into account the effect of any flood defences in an area. Although one should always remember that flood defences reduce, but do not completely eliminate the risk flooding, as they can be overtopped or fail.
The map also contains information on location of flood defences, Areas Benefitting from Flood Defences and Shoreline Management Plan & Coastal Erosion. Many layers, such as the Shoreline Management Plan & Coastal Erosion layer, reveal more information if you use the easy to miss ‘Identify’ tool in the top right hand corner.
Want to know more?
In our third and final blog on the new flood maps coming to Wales, we will look at the new Flood Map for Planning that is expected to be launched alongside the update to Development and Flood Risk planning policy TAN15 in Spring 2021.
Email George Baker for more information about the new flood maps for Wales.