Background to the Past Flood Event records
Between the years 2004 to 2006 the OPW developed the Flood Hazard Mapping website, www.floodmaps.ie, which provided information about the location of known flood events in Ireland and showed supporting information in the form of reports, photos and press articles about those floods. During this time a huge data collection program was undertaken, visiting over 50 organisations (mainly local authorities and national organisations, eg Waterways Ireland, DoEHLG, and Teagasc) to collect and collate a vast array of information about flooding. The type of information varied from photographs of flood events, to consultants' reports, recordings from gauging stations, eyewitness accounts from staff plus letters from members of the public and minutes of meetings with key officials.
All this information was reviewed, verified, assessed and catalogued to create a National Flood Data Archive. From this the floods were mapped and uploaded to the website. Since 2006, as flood events occurred or as information was submitted to OPW from different sources, including information from the public, new floods and reports were added to the website on an ongoing basis.
In late 2017, when this website www.floodinfo.ie was developed, this data was migrated across to this new website and is now viewable by turning on the “Past Flood Events” layer which enables this past flood event data to be viewed simultaneously with predictive flood mapping layers.
Contents and Information Available
Past Flood Events
A Past Flood Event is defined as the occurrence of recorded flooding at a given location on a given date or on a recurring basis. The event is derived from available Flood information documentation including Flood Event Reports, news articles, archive information and photos.
Past Flood Event Locations
Past Flood Event Locations are represented on the map with a point symbol placed at the approximate location of the flood. A flood point symbol is placed at any location mentioned in a report giving details of a flood event. Where more than one flood has occurred in the same location, and to denote a location with recurring flooding, a multiple flood point symbol is used.
To get more information, such as Flood Event Reports or photos where available, regarding these events click on the flood point symbol which will bring up a “Flood Summary” pop-up in which the information available regarding that flood event is summarised and further information can be accessed.
Mapped Information is not available on the extent of the area flooded.
Flood Summary
The Flood Summary provides the user with specific details about the Flood Event. Such summary details include:
- Flood event name
- Peak Date (of the Flood Event)
- County (there can be more than one county listed if the area flooded crossed county borders)
- Flood Quality Code. Each flood is ranked from 1 to 4 depending on the quality of the information available about the flood.
- Additional Information
Flood Event Reports
Flood Event Reports are reports of past events that have been complied using the information submitted by Local Authorities and CFRAM Consultants, via the Flood Event Report Form. These can been viewed and downloaded in .pdf format.
News articles, archive information and photos
New articles, archive information and photos of past events are also available to view and download. This information is comprised of information received from various sources such as anecdotalevidence and eye witness reports, old newspaper articles, most recent news reports, Local Authorities records and CFRAM Consultants.
Legends and Quality Codes
Flood Point Symbol
The Flood Point symbol marks the approximate location of a past flood.
Multiple / Recurring Flood Symbol
A Multiple / Recurring Flood Point symbol marks the approximate location of an area that
has been affected by more than one Flood Event.
Quality Codes
The Quality Codes are used to classify the flood event and report information according to the reliability and content of the information. Data presented in the Flood Summary ranges from photographs known to have been taken at the height of clearly identified Flood Events to documented recollections of events by Local Authority field staff.
As a result of a verification process each information item collected from source bodies is classified and graded as follows:
- Code 1: Contains, for a given flood event at a given location, reliably sourced definitive information on peak flood levels and/or maximum flood extents.
- Code 2: Contains, for a given flood event at a given location, reliably sourced definitive information on flood levels and/or flood extents. It does not however fully describe the extent of the event at the location.
- Code 3: Contains, for a given location, information that, beyond reasonable doubt, a flood has occurred in the vicinity.
- Code 4: Contains flood information that, insofar as it has been possible to establish, is probably true.
Press articles are not verified or classified as described above. These are presented as published in the newspapers in which they appear.
Completeness and Accuracy
Completeness
The National Flood Data Archive is not a comprehensive catalogue of all past (fluvial/tidal) flood events in Ireland; material was presented for inclusion by source bodies from their available records at their discretion. However, the Archive is still the most comprehensive and complete collection of data on past flood events available in the country. New information is verified and checked for duplication before addition to the archive.
Accuracy
All the information presented in the “Past Flood Events” layer has been verified and classified according to the quality of the content. Flood points have been mapped to the best available information describing their location and have also been classified according to the quality of the supporting report information. The quality codes used to classify the flood information are described in Quality Codes above.
The presence of a flood point symbol is only indicative of the approximate location of a flood and is not expected to be accurate to the level of individual properties.
The absence of a flood indicator (point or area symbol) for a past flood event in any particular location does not mean that flooding has never occurred in that area nor does it mean that that area may not be liable to flooding in future. A location may be at risk from flooding but information on past floods at that location may not be available.
Reliability
The reliability of all the flood information (with the exception of the press articles) is assessed as part of the verification process and is reflected in the quality codes (see following question) assigned to both the flood events and flood reports. The highest quality code (1) is assigned to the most detailed information about a flood (including the peak time and levels, dates, known locations, engineer’s reports, and so on). Where information is of lower quality (such as approximate dates, peak times not known, levels not recorded, location estimated) a lower quality code is assigned. In this way, the reliability of the information can be assessed.
Updates and Revisions
The National Flood Data Archive, which provides all the information for presentation on the website, is continually being updated and added to by the OPW. Information on new and past flood events can be, and is, submitted from a variety of sources (government, private and individuals) for inclusion as it becomes available. All information is checked and classified first, then approved before it appears on the website.