Flood Risk Assessment Wales (FRAW)
Asesiad Perygl Llifogydd Cymru

  • English
  • wel
  • All

Flood Risk Assessment Wales provides a national assessment of risk flooding from Rivers, the Sea and Surface Water and Small Watercourses. The assessment takes into account flood defences and combines new, national-scale modelling with detailed local-scale models to categories risk into 3 bands, labelled ‘High’, ‘Medium’ and ‘Low’ risk.

Mae Asesiad Perygl Llifogydd Cymru yn darparu asesiad cenedlaethol o berygl llifogydd o afonydd, y môr a dŵr wyneb a chyrsiau dŵr bychain (gan ddisodli set ddata Perygl Llifogydd o Afonydd a'r Môr).


Mae'r asesiad yn ystyried amddiffynfeydd rhag llifogydd ac yn cyfuno gwaith modelu newydd ar raddfa genedlaethol â modelau manwl ar raddfa leol i greu tri band o ddosbarthiad risg o dan y labeli 'Uchel', 'Canolig' ac 'Isel'.


Ar gyfer Afonydd a Dŵr Wyneb a Chyrsiau Dŵr Bach:


Mae risg ‘Uchel’ yn golygu bod siawns o lifogydd o fwy nag 1 mewn 30 (3.3%) bob blwyddyn yn yr ardal hon.

Mae risg ‘Ganolig’ yn golygu bod siawns o lifogydd o rhwng 1 mewn 100 (1%) ac 1 mewn 30 (3.3%) bob blwyddyn mewn ardal.

Mae risg ‘Isel’ yn golygu bod siawns o lifogydd o rhwng 1 mewn 1000 (0.1%) ac 1 mewn 100 (1%) bob blwyddyn mewn ardal.

Ar gyfer y Môr:


Mae risg ‘Uchel’ yn golygu bod siawns o lifogydd o fwy nag 1 mewn 30 (3.3%) bob blwyddyn yn yr ardal hon.

Mae risg ‘Ganolig’ yn golygu bod siawns o lifogydd o rhwng 1 mewn 200 (0.5%) ac 1 mewn 30 (3.3%) bob blwyddyn mewn ardal.

Mae risg ‘Isel’ yn golygu bod siawns o lifogydd o rhwng 1 mewn 1000 (0.1%) ac 1 mewn 200 (0.5%) bob blwyddyn mewn ardal.

Mae'r asesiad risg yn ystyried effaith amddiffynfeydd rhag llifogydd pan fo gennym wybodaeth. Mae amddiffynfeydd rhag llifogydd yn lleihau llifogydd, ond nid ydynt yn atal y siawns o lifogydd yn gyfan gwbl oherwydd gall dŵr fynd drostynt neu gallant fethu.


Mae gwybodaeth perygl llifogydd ar gyfer pob ffynhonnell wedi'i chreu fel 'croen nionyn', h.y. heb unrhyw ddata sy'n gorgyffwrdd rhwng bandiau risg unigol. Dylid cyfuno'r bandiau risg hyn a'u harddangos fel un haen ar gyfer pob ffynhonnell llifogydd.


Os dangosir data ar ffurf mapiau i eraill, dylid defnyddio graddfeydd map priodol o ystyried natur ddangosol y modelu. Dylid ei ddangos gyda graddfa chwyddo mwyaf o 1:5,000 a defnyddio mapio sylfaen o 1:10,000 i roi cyd-destun.


Mae'r mapio llifogydd yn seiliedig ar ardaloedd sydd mewn perygl o ddioddef llifogydd ac nid yw'n benodol ar gyfer eiddo unigol. Nid yw CNC yn cadw gwybodaeth am adeiladwaith eiddo unigol a allai effeithio ar ba un ai y gallai llifogydd o ddyfnder penodol fynd i mewn i eiddo ac achosi difrod. Mae ein gwybodaeth fel y cyfryw wedi'i chynhyrchu i nodi ardaloedd cyffredinol a allai fod mewn perygl o ddioddef llifogydd ar gyfer ymchwiliad pellach.


Cydraniad gofodol y data:


Modelu ar raddfa genedlaethol a wnaed gan ddefnyddio cydraniad grid o 2m.


Modelu ar raddfa leol a wnaed gan ddefnyddio gwahanol gydraniadau, yn nodweddiadol rhwng 2m – 10m.


Mae rhagor o wybodaeth ar gael yn adroddiad prosiect FRAW (2019) a thudalen we CNC Deall eich canlyniadau perygl llifogydd ( https://naturalresources.wales/flooding/managing-flood-risk/understanding-your-flood-risk-results?lang=cy ) i gael mwy o wybodaeth am ein data perygl llifogydd a sut y dylid ei ddefnyddio.


Mae'r Lefel Perygl dan Adolygiad yn nodi lleoliadau lle mae ein hasesiad risg o dan adolygiad dros y chwe mis nesaf oherwydd argaeledd gwybodaeth newydd o fodelau ar raddfa leol.


Datganiad priodoli


Yn cynnwys gwybodaeth gan Cyfoeth Naturiol Cymru © Corff Adnoddau Naturiol Cymru a hawliau cronfa ddata. Cedwir pob hawl. Mae’r amcangyfrifon o lif llifogydd yn seiliedig ar fethodoleg a data FEH, © a hawliau cronfa ddata UKCEH 2015*, gan ddefnyddio FEH WinFap a/neu'r Revitalised Flood Hydrograph Modelling Tool © Wallingford HydroSolutions Limited [Y FLWYDDYN BRESENNOL] neu ei drwyddedwyr. Mae disgrifyddion y dalgylchoedd neu unrhyw ddarnau eraill a gymerwyd o Wasanaeth Gwe FEH, os ydynt wedi’u darparu, dan © a hawliau cronfa ddata UKCEH 2015*. Cedwir pob hawl. *UKCEH 2015. Gwasanaeth Ar-lein y Flood Estimation Handbook (FEH), UK Centre for Ecology & Hydrology, Wallingford, Swydd Rhydychen, y DU. Yn cynnwys Data’r Arolwg Ordnans. Rhif trwydded yr Arolwg Ordnans: AC0000849444. Hawlfraint a Hawliau Cronfa Ddata y Goron.

Identification

Dynodydd
Identifier
NRW_DS124841
Teitl Amgen
Alternative Title
  • Flood Risk from Surface Water and Small Watercourses
  • Flood Risk from the Sea
  • Flood Risk from Rivers
Laith Metadata
Metadata Language
English
Lineage

For Rivers and Surface Water and Small Watercourses:

- ‘High’ risk means that each year, this area has a chance of flooding of greater than 1 in 30 (3.3%)

- ‘Medium’ risk means that each year, an area has a chance of flooding of between 1 in 100 (1%) and 1 in 30 (3.3%).

- ‘Low’ risk means that each year, an area has a chance of flooding of between 1 in 1000 (0.1%) and 1 in 100 (1%).


For the Sea:

- ‘High’ risk means that each year, this area has a chance of flooding of greater than 1 in 30 (3.3%)

- ‘Medium’ risk means that each year, an area has a chance of flooding of between 1 in 200 (0.5%) and 1 in 30 (3.3%).

- ‘Low’ risk means that each year, an area has a chance of flooding of between 1 in 1000 (0.1%) and 1 in 200 (0.5%)


The risk assessment takes into account the effect of flood defences where we have information. Flood defences reduce, but do not completely stop the chance of flooding as they can be overtopped or fail.


Flood risk information for each source has been created as ‘onion-skins’, i.e. with no overlapping data between individual risk bands. These risk bands should be combined and displayed a single layer for each flood source.


If data is displayed in map form to others, appropriate map scales should be used given the indicative nature of the modelling. It should be shown with a maximum zoom scale of 1:5,000 and that base mapping of 1:10,000 is used to give context.


The flood mapping is based on areas at risk of flooding and is not specific to individual properties. NRW doesn’t hold information about an individual property’s construction that might affect whether flooding of a certain depth could enter a property and cause damage. As such, our information has been produced to identify general areas potentially at risk of flooding for further investigation.


Spatial resolution of the data:

National scale modelling undertaken at 2m grid resolution. Local scale modelling undertaken at different resolutions, typically between 2m – 10m.
Additional Information

More information is available in the FRAW (2019) project report and NRWs Understanding your flood risk results webpage ( https://naturalresources.wales/flooding/managing-flood-risk/understanding-your-flood-risk-results?lang=en ) for more information on our flood risk data and how it should be used.

Dyddiad cyfeirnod y set ddata (Cyhoeddiad)
Dataset Reference Date (Publication)
2026-05-21

Temporal Extent

Begin date
2018-09-01
 
Categori pwnc
Topic category
  • Inland waters
    Inland waters
  • Environment
    Environment
Perchennog
Owner
  Natural Resources Wales (NRW) -
Maes-y-Ffynnon, Penrhosgarnedd, Bangor, Gwynedd, LL57 2DW, Wales
http://naturalresources.wales/?lang=en
Cychwynnwr
Originator
  Natural Resources Wales (NRW) -
Maes-y-Ffynnon, Penrhosgarnedd, Bangor, Gwynedd, LL57 2DW, Wales
http://naturalresources.wales/?lang=en
 

Extent

Extent

Hyd
Geographic Extent
Wales (WLS)
N
W
E
S
Map representing the geographic extent of the dataset


 
 

Distribution

Dosbarthiad
Distribution

Fformat - Math a Disgrifiad
Format Type and Description
  • Geographic Information System ( Unknown )

    Specification

    ESRI Feature Class

Lleolwr Adnoddau
Resource Locator
Download Data and Web Service ( WWW:LINK-1.0-http--link )
Lleolwr Adnoddau
Resource Locator
Web Mapping Service ( OGC:WMS )
 

Quality

Ansawdd Data
Data quality

Cwmpas Ansawdd
Quality Scope
Dataset
Dataset
Cydymffurfiad
Conformity
Commission Regulation (EU) No 1089/2010 of 23 November 2010 implementing Directive 2007/2/EC of the European Parliament and of the Council as regards interoperability of spatial data sets and services
Explanation

This dataset has not been assessed for conformance to the referenced INSPIRE regulation.
Degree
false
Lineage

For Rivers and Surface Water and Small Watercourses:

- ‘High’ risk means that each year, this area has a chance of flooding of greater than 1 in 30 (3.3%)

- ‘Medium’ risk means that each year, an area has a chance of flooding of between 1 in 100 (1%) and 1 in 30 (3.3%).

- ‘Low’ risk means that each year, an area has a chance of flooding of between 1 in 1000 (0.1%) and 1 in 100 (1%).


For the Sea:

- ‘High’ risk means that each year, this area has a chance of flooding of greater than 1 in 30 (3.3%)

- ‘Medium’ risk means that each year, an area has a chance of flooding of between 1 in 200 (0.5%) and 1 in 30 (3.3%).

- ‘Low’ risk means that each year, an area has a chance of flooding of between 1 in 1000 (0.1%) and 1 in 200 (0.5%)


The risk assessment takes into account the effect of flood defences where we have information. Flood defences reduce, but do not completely stop the chance of flooding as they can be overtopped or fail.


Flood risk information for each source has been created as ‘onion-skins’, i.e. with no overlapping data between individual risk bands. These risk bands should be combined and displayed a single layer for each flood source.


If data is displayed in map form to others, appropriate map scales should be used given the indicative nature of the modelling. It should be shown with a maximum zoom scale of 1:5,000 and that base mapping of 1:10,000 is used to give context.


The flood mapping is based on areas at risk of flooding and is not specific to individual properties. NRW doesn’t hold information about an individual property’s construction that might affect whether flooding of a certain depth could enter a property and cause damage. As such, our information has been produced to identify general areas potentially at risk of flooding for further investigation.


Spatial resolution of the data:

National scale modelling undertaken at 2m grid resolution. Local scale modelling undertaken at different resolutions, typically between 2m – 10m.
 

Keywords

Allweddair
Keywords

GEMET - INSPIRE themes, version 1.0
Math
Type
Theme
Theme

Dyfyniad
Citation

Dyddiad (Cyhoeddiad)
Date (Publication)
2008-06-01
Code
geonetwork.thesaurus.external.theme.httpinspireeceuropaeutheme-theme

Allweddair
Keywords

NRW Thesaurus
  • flood modelling
  • flood risk
Math
Type
Theme
Theme

Dyfyniad
Citation

Dyddiad (Cyhoeddiad)
Date (Publication)
2026-08-27
Code
geonetwork.thesaurus.local.theme.converted_nrw-keywords
 

Spatial Reference System

Code
British National Grid (EPSG::27700)
 

Content

Gwybodaeth Cynnwys
Content Information

Proffil CNC
NRW Profile

Elfennau CNC
Custom Elements

 

Constraints

Constraints

Limitations on Public Access and Use

Math o Gyfyngiad
Restriction type
Other restrictions
Other restrictions
 

Access Constraints Directive

Limitations
no limitations
 

Access Constraints Text

Other constraints

There are no access restrictions on this data. NRW may release, publish or disseminate it freely.
 

Use Constraints

Cyfyngiadau Defnyddio
Use constraints type
Other restrictions
Other restrictions
Other constraints

© CNC/NRW and UKCEH. Data may be re-used under the terms of the Open Government Licence providing it is done so, acknowledging both the source and NRW's copyright. It is the recipient's responsibility to ensure the data is fit for the intended purpose.
 

Attribution Statement

Other constraints

Contains Natural Resources Wales information © Natural Resources Body for Wales and database right. All rights reserved. Flood flow estimates are based upon FEH methodology and data, © and database right UKCEH 2015*, using WinFap FEH and/or the Revitalised Flood Hydrograph Modelling Tool © Wallingford HydroSolutions Limited [CURRENT YEAR] or its licensors. Catchment descriptors or other extracts from the FEH Web-Service, if supplied, are © and database right UKCEH 2015*. All rights reserved. *UKCEH 2015. The Flood Estimation Handbook (FEH) Online Service, UK Centre for Ecology & Hydrology, Wallingford, Oxon, UK. Contains Ordnance Survey Data. Ordnance Survey Licence number AC0000849444. Crown Copyright and Database Right.
 

Licence

Other constraints
Open Government Licence
 
 
 

Metadata

Metadata

Dynodydd Ffeil
File Identifier
4f4c4942-4343-5764-6473-313234383431 XML
Laith Metadata
Metadata Language
English
Math o adnodd
Resource type
Dataset
Dataset
Dyddiad Metadata
Metadata Date
2026-09-30T13:55:21.792Z
Enw Safonol Metadata
Metadata Standard Name
NRW
Fersiwn Metadata
Metadata Standard Version

1.0

Pwynt Cyswllt
pointOfContact
  Natural Resources Wales (NRW) -
Maes-y-Ffynnon, Penrhosgarnedd, Bangor, Gwynedd, LL57 2DW, Wales
http://naturalresources.wales/?lang=en
 
 

Publishing Body

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