Sea Mills to Severn Beach - Yate to Sea Mills - Cancelled - High Tide

[sleepy_hollow]

Yesterday the forecast for today was sunny, so I planned a day's cycling from Severn Beach, returning from Yate, intending to travel on the 0904 from Sea Mills, 2K14. I noticed that the Environment Agency had issued flood warnings for the Avon from Sea Mills to Conham, checked the tide forecast, which was for 12.9 m at 0904, just enough to get onto the quay at Sea Mills and checked Real Time Trains, noting that the full service was running, so nothing to worry about. This morning I checked again, and by 0800 cancellations were beginning to appear, with the services turning round at Clifton Down. Oddly the 0904 was not shown as cancelled on the summary view, but the detail showed it as cancelled from Clifton Down, although timings were shown all the way to SVB. At this point I cancelled the train trip and drove to the Mendips to walk over Dolebury and Black Down. There was water in the usual place on the Portway, under the suspension bridge, possibly about 50 mm on the river side at about 0930.

The GWR notice said that the line would remain closed until about 1200 so that Network Rail could inspect the 'viaduct' in daylight. In fact trains were cancelled until after 1700.

After we got through the autumn equinox without trouble, including occasions when the Closure Mark went about 500 mm under I assumed that equinoctial tides would not be a problem, and that the railway had forgotten about closure marks, but unfortunately this seems not to be the case, and we have England's only tidal railway service. Tomorrow's prediction is for 12.8 m, and we probably have about three more high tides before the spring equinox period is over.

 

[Dai Corner]

The water level will depend on wind speed and direction and previous rainfall as well as the tides.

Similar closures occur on other lines such as the Looe Branch

 

[sleepy_hollow]

Which raises an interesting question. Were these lines built as tidal, or did they become tidal? I suppose the route past Dawlish could be described as tidal, but was presumably not intended to be so, and I know of no evidence that the Clifton Extension was intended to be susceptible to tides. Looe was not affected on Monday, although obviously at the same point in the Atlantic tide cycle as SML.

If I am able to check the tide mark tomorrow I expect to find nothing unusual, probably just below where it would flow into the allotments. Using 'flooding' or 'severe flooding' to describe the events at SML is stretching the meaning of the word. 'Flooding' should be reserved for water getting inside the boundary fence, fish on the ballast and so on.

 

[Llanigraham]

Also closed a section of the Machynlleth to Aberystwyth due to the high tide.
They used to have a problem at Dovey Junct, but raised the line slightly, which seems to have alleviated it.

And I suspect that when built they didn't have the problem but the gradual increase in sea depths has caused it.

 

[Dai Corner]

Which raises an interesting question. Were these lines built as tidal, or did they become tidal? I suppose the route past Dawlish could be described as tidal, but was presumably not intended to be so, and I know of no evidence that the Clifton Extension was intended to be susceptible to tides. Looe was not affected on Monday, although obviously at the same point in the Atlantic tide cycle as SML.

If I am able to check the tide mark tomorrow I expect to find nothing unusual, probably just below where it would flow into the allotments. Using 'flooding' or 'severe flooding' to describe the events at SML is stretching the meaning of the word. 'Flooding' should be reserved for water getting inside the boundary fence, fish on the ballast and so on.

I think it's a case of the railway being more cautious these days, together with deterioration of earthworks and structures. There were cancellations on the Looe branch yesterday I believe.

Perhaps the reason should be given as 'risk of flooding' or 'unusually high water levels'?

 

[Mcr Warrior]

We had a similar discussion about high tides and possible flooding on this same stretch of track (Severn Beach line) almost a year ago...

Sea flooding on Severn Beach Line (22/02/23)

Severn Beach Line trains have been cancelled beyond Clifton Down since the 0954 at SML this morning, due to 'flooding by the sea'. (1) What has happened? High tide at Sea Mills was 0854 today, 13m, which is fairly high and will just bring it onto the quay, but the railway is about 2 m higher...

www.railforums.co.uk

 

[sleepy_hollow]

And still we are no wiser as to what is going on, whether administrative muddle or new procedures and limits. So far we seem to have the same situation as list year, where the first predicted highest tide produces a closure after which high tides are ignored. It is almost as if the first highest tide of the year is being used as an annual requalification exercise.

The highest prediction for this full moon is 11.3 m, so we must wait for the new moon in a fortnights time to see what happens.

 

[stuu]

The weather has a big influence, tides rise higher under low pressure weather systems, and wind pushes them even further - that's what a storm surge is. If the highest tide happens on a tranquil sunny day then the water won't rise as high

 

[sleepy_hollow]

This is the Sea Mills new moon high tide at its maximum on Tuesday 12th March 2024, two days ago. Predicted as 13.2 m at 0843. The following day, Wednesday 13th was predicted at 12.8 m but still produced a timetable only planned to start at midday.




Generally similar level to the 2014 example in my older picture, below, allowing for the 2014 picture being possibly half an hour ater the peak. The level on the bridge piers seems surprisingly similar. The Environment Agency flood warning referred to a surge above astronomical levels, about 300 mm I think.



Tidal predictions:



The travel arrangements included 8 seater taxis on Tuesday, presumably from the rail replacement stop 1 km away in Shirehampton Road, and a statement that the bridge would reopen after inspection. The Wednesday arrangement does not seem to mention taxis, but hopes that local buses will accept tickets. On both days the trains seem to have started later than planned, and on Tuesday unplanned cancellations resumed about the time of the evening high tide.




Unlike Looe there does not seem to be the excuse of water on the level crossing so we seem to be left with administrative muddle or serious structural change. It might speed up reopening if a resident structural engineer was appointed so that the bridge could be inspected as soon as the closure mark came into view.

 

[sleepy_hollow]

And today, Wednesday 10th March 2024, with an astronomical tide prediction of 13.0 m at 0919, with the closure mark then well under trains ran normally all day, including aa the tide turned.



High tide at 0920 BST.



The 0931 outbound:



Yet yesterday, with an equal predicted height the timetable collapsed completely, due to 'severe flooding'.




That is probably it for this year, as the autumn equinox tides are not currently as high as the spring.

 

[The exile]

Weren’t there pretty strong winds on Tuesday which could have made things a lot worse (or maybe did)

 

[sleepy_hollow]

The tide marks suggest nothing abnormal for a 13.0 m prediction on Tuesday, perhaps 50 mm higher than the similar prediction for the Wenesday tide that I photographed on the turn. That is the problem with 'severe flooding' as a reason for closure, no one knows where it is, everyone imagines ballast washed out, fish on the sleepers, an irresistible act of god rather than someone remembering about the closure mark.



Interestingly, there is now a notice advertising an application for permission to install rock bags round pier 1, to prevent scouring. Perhaps scouring is the reason for the new caution, although I doubt if scouring is much less with 12.7 m, or even 12.0 m, than with 13.0 m. Which still leaves the question of what the closure mark means if trains can run with it well under water?

And apart from scouring, what has happened to the alleged imminent programme for general repair of the truss struts?