Breadcrumbs

Tidal surge: A reasonable response?

The tidal surges on 13-14th January have left a lot of questions in peoples’ minds.  This is the third occasion when the Environment Agency (EA) warned that there might be a disaster.  Some have lamented the waste of money, executing a plan for a disaster that did not happen.  Some may even decide to stay put next time, rather than leave their homes.  I raised this with the Environment Agency following their post operational review with the emergency services. 

Their decisions are based on “best estimates” of what heights tides will reach, and when.  This depends entirely on the relationship between the normal high tide the height and timing of the tidal surge.  They look at “reasonable worst case scenarios” and Met Office advice about tidal surges, but the final decision on an evacuation rests with the “Gold Command”.  This is our Chief Constable or one of his Deputy Chief Constables.  He or she has to make judgements well in advance, based on “reasonable worst case scenarios”.  Most people would agree: better safe than sorry. 

In this case, it was particularly difficult to make judgements as weather predictions were changing very quickly.  Even though the Friday lunchtime tide was lower than expected, it could not be taken as an indication that the next high tide would be lower too.  A force 8 gale warning was issued, but as often happens, the wind force was lower than forecast.  Most crucially, at no point did the tidal surge coincide with the normal High Water.  Jaywick was evacuated because parts of the sea wall there are slightly lower than elsewhere, and so there was considered to be a real danger of over-topping.  

I also asked why the EA put out tide warnings giving tidal heights we don’t recognise.  Marine tide tables for navigation give predicted heights “above Chart Datum” (above the lowest astronomical tide at that geographical location).  The EA shows tidal heights above “Average Ordnance Datum Newlyn” which is how we show altitudes on maps.  I have asked the EA to put up a conversion table on their website showing the difference between the two so more people can relate the EA data to what they are used to.

Finally, thank you to all the staff of the EA, the police, the fire service, local councils and all the others who worked through the night to keep people safe.