- Are waves included in the Coastal Flood Boundaries?
- Coastal Flood Boundaries - additional help and further information
- How are levels within ‘Inland Extensions’ or ‘Estuaries’ derived?
- How can I generate my Base Tide Curves?
- How does the Coastal Flood Boundaries inform us about flood risk around the UK coast?
- How is sea level rise accounted for in the Coastal Flood Boundaries?
- How often is the Coastal Flood Boundaries dataset updated?
- How should I use Coastal Flood Boundaries levels in estuaries and tidal rivers?
- I am concerned about the large differences in values in some locations and the effects on my project
- 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?
- 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 are the Coastal Flood Boundaries?
- What are the key outputs of Coastal Flood Boundaries 2018?
- What has been done to update the Coastal Flood Boundaries in 2018?
- What has changed in Coastal Flood Boundaries 2018?
- What information is included in the extreme sea levels shapefiles?
- What is meant by Annual Exceedance Probability (AEP) and which extreme sea level probabilities are included?
- What is the accuracy of the Coastal Flood Boundaries extreme sea levels?
- What is the base year for Coastal Flood Boundaries levels?
- What is the vertical datum of the Coastal Flood Boundaries Level?
- Where can I access the Coastal Flood Boundaries data and guidance documents?
- Who should use the Coastal Flood Boundaries (CFB) data?
- Why are regular updates, and therefore likely change in the estimates, necessary?
How are levels within ‘Inland Extensions’ or ‘Estuaries’ derived?
Created: 03 October 2019 Updated: 03 October 2019
The inland extensions (from here-on ‘estuaries’) are calculated using the following methods. A shapefile is available from coastal modelling teams to find out which method has been used to derive levels for each point within estuaries:
No data. Where no observed data were available an estuary relationship was established by borrowing a relationship from a similar estuary or assuming that the gradient is flat (Scotland only).
Observed data. Upstream of the downstream boundary levels were derived using an estuary relationship based on observed data expressed as a gradient.
Modelled data. In some cases levels were taken directly from existing coastal modelling studies where these studies were deemed appropriate. Results were taken from the modelling of extreme coastal events only. A background fluvial flow may have been included such as the index flood QMED, but the results do not include any joint probability of extreme fluvial and coastal event modelling. All levels derived using this method are labelled ‘ESTUARY_’ in the Location field of the shapefile CFB_Extreme_Sea_Levels_Estuary_2018.shp available on http://data.gov.uk .
The CFB 2018 estuary and tidal river levels are based on the interpolation of modelled levels including defences and so do not necessarily represent the scenario in which there are no flood defences. Flood defences can constrain coastal flood waters, resulting in elevated water levels upstream. Similarly, levels based on gauge analysis at upstream locations represent the scenario in which defences exist.
As improved modelling becomes available following this 2018 update, the CFB ‘ESTUARY’ levels may be subject to review and further updates. The models in this 2018 update also do not include all models available at the time of this report was written. Detailed models have been included as a priority in regions of particular interest. Further locations will be added in the future.