- Coastal Flood Boundaries - additional help and further information
- Where can I access the Coastal Flood Boundaries data and guidance documents?
- How is sea level rise accounted for in the Coastal Flood Boundaries?
- I am concerned about the large differences in values in some locations and the effects on my project
- Levels have fallen in my area of interest since the previous Coastal Flood Boundaries update. How can this be when sea levels are known to be rising?
- What has changed in Coastal Flood Boundaries 2018?
- I’ve been given mean high water springs (MHWS) and highest astronomical tide (HAT) predicted Tide Levels by another source. They don’t match up to those in the Coastal Flood Boundaries. Which should I use?
- How are levels within ‘Inland Extensions’ or ‘Estuaries’ derived?
- How should I use Coastal Flood Boundaries levels in estuaries and tidal rivers?
- What are the key outputs of Coastal Flood Boundaries 2018?
- What has been done to update the Coastal Flood Boundaries in 2018?
- Why are regular updates, and therefore likely change in the estimates, necessary?
- How often is the Coastal Flood Boundaries dataset updated?
- How can I generate my Base Tide Curves?
- Are waves included in the Coastal Flood Boundaries?
- What information is included in the extreme sea levels shapefiles?
- What is the accuracy of the Coastal Flood Boundaries extreme sea levels?
- What is the vertical datum of the Coastal Flood Boundaries Level?
- What is the base year for Coastal Flood Boundaries levels?
- What is meant by Annual Exceedance Probability (AEP) and which extreme sea level probabilities are included?
- How does the Coastal Flood Boundaries inform us about flood risk around the UK coast?
- Who should use the Coastal Flood Boundaries (CFB) data?
- What are the Coastal Flood Boundaries?
What is the vertical datum of the Coastal Flood Boundaries Level?
Created: 03 October 2019 Updated: 03 October 2019
The return levels presented in this report are generally relative to the main tide gauge benchmark, which has a fixed height relative to Ordnance Datum Newlyn (ODN) and Ordnance Datum Belfast (in Northern Ireland). Sites relative to local datums include Stornoway, Lerwick and St Mary’s.
ODN is referred to here as the height above mean sea level at Newlyn from 1950 to 1968. Comparisons of the return levels can only be made with other data relative to the same datum (that is, ODN). Heights measured using a GPS can be converted to ODN via the spatial surface of the transformation model OSGM15, or previously OSGM02.