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

[sleepy_hollow]

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, adequate margin against any conceivable tide. The line probably remains above maximum high tide until about the level crossing under the M5 at Avonmouth.

(1) https://www.journeycheck.com/greatwesternrailway/

Due to the sea flooding the railway between Clifton Down and Severn Beach the line is blocked.
Train services running to and from these stations may be cancelled or delayed. Disruption is expected until 21:00 22/02.
Local bus ticket acceptance is in place.

 

[HSTEd]

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, adequate margin against any conceivable tide. The line probably remains above maximum high tide until about the level crossing under the M5 at Avonmouth.

(1) https://www.journeycheck.com/greatwesternrailway/

Meteorological effects can compound tidal effects to result in a sea level significantly higher than would be expected if there was no atmosphere above the ocean.

 

[Baxenden Bank]

if there was no atmosphere above the ocean.

 

[RupturedDuck]

Maybe precautionary as there were 4 Severn Bore expected today. That would suggest some rather extraordinary conditions as 4 bore seems unusual?

 

[sleepy_hollow]

Maybe precautionary as there were 4 Severn Bore expected today. That would suggest some rather extraordinary conditions as 4 bore seems unusual?

There was a flood warning, now withdrawn, for Avonmouth this morning. WIthdrawn as not expected to be repeated in this tide cycle. The 4* bore warning appears to be this evening, for a slightly lower tide. (2) Presumably the water has dribbled over the railway somewhere between the Lamplighters and Holesmouth. The cancellations started after the high tide time. It is difficult to interpret 'due to sea flooding the railway' as anything different from 'the sea flooded the railway'.

(2) https://www.severn-bore.co.uk/2023_times.html

 

[Dai Corner]

I suspect that this was due to forecast water levels rather than actual flooding.

I'd have said the railway is most vulnerable where it's close to the river Avon in the Sea Mills / Shirehampton area? Hence turning back at Clifton Down.

 

[sleepy_hollow]

I suspect that this was due to forecast water levels rather than actual flooding.

I'd have said the railway is most vulnerable where it's close to the river Avon in the Sea Mills / Shirehampton area? Hence turning back at Clifton Down.

Two metres may be an overestimate for the track freeboard at Sea Mills, but under the M5, at the far end of Lamplighters Marsh it is probably down on the foreshore.

Here, Sea Mills station in 2014, with the coastguard departing, and then the train.

 

[Dai Corner]

This morning Journeycheck says

Cancellations to services between Bristol Temple Meads and Severn Beach via Clifton Down
Due to a river flooding the railway at Sea Mills all lines are blocked. Disruption is expected until 13:00 23/02.
Train services between Bristol Temple Meads and Severn Beach via Clifton Down and Avonmouth may be cancelled or revised. All stations between Clifton Down and Severn Beach will not be served.
Customer Advice
Due to the high tides on the River Avon at Sea Mills, the Severn Beach line is closed between Clifton Down and Severn Beach.

A GWR shuttle is operating between Bristol Temple Meads and Clifton Down.

 

[Mcr Warrior]

How far upstream is the River Avon tidal? (And is Sea Mills station / the nearby A4 overbridge, about as far along as the Severn Beach branch line runs to/from Bristol Temple Meads, which is more-or-less still immediately adjacent to the riverside, and thus liable to possible flooding at high tide?)

 

[Dai Corner]

How far upstream is the River Avon tidal? (And is Sea Mills station / the nearby A4 overbridge, about as far along as the Severn Beach branch line runs to/from Bristol Temple Meads, which is more-or-less still immediately adjacent to the riverside, and thus liable to possible flooding at high tide?)

It's tidal as far as Hanham, in the east of Bristol.

Sea Mills to Shirehampton is probably the section most vulnerable to flooring.

 

[sleepy_hollow]

The river is tidal, up the New Cut, through the city centre. Sea Mills is the lowest point between Clifton Down tunnel and the rise to Horseshoe Bend, where it is well up the cliff, but SML is still on a low embankment. I think it probably gets lower at the Avonmouth end of Lamplighters Marsh and through Avonmouth

I saw the Bristol Post report identifying Sea Mills as the location of flooding and went down to see this phenomenon, getting there about thirty minutes after high tide, predicted to be about 200 mm down on the peak at about 0930. The tide was not unusual, just onto the quay, no sign that the owner of the Old Signal Station had needed to sweep mud away and the highest recent local tide mark was near the quay, no sign that water had been anywhere near the railway.

A 12.8 m tide has never stopped the trains before.

Seen from upstream - todays tide line visible on the grass.


Seen through the road bridge. The mud under the arch was probably wet yesterday, but not this morning. It is quite normal for trains to run with the tide up under this arch.


From the station crossing the highest recent tide mark can be seen beyond the trailer. (Edit: Historic highest tides have reached the entrance to the allotments, just above the garage and trickled down towards the allotments, without affecting the trains.)


General view from the quay, todays incursion shown by the wet mud.


We seem to have a new phenomenon, like snow, that puts the railway in a catatonic trance, without anyone else noticing.

 

[Meerkat]

Any worries about that bridge/viaduct when the water gets high??

 

[Dai Corner]

The river is tidal, up the New Cut, through the city centre. Sea Mills is the lowest point between Clifton Down tunnel and the rise to Horseshoe Bend, where it is well up the cliff, but SML is still on a low embankment. I think it probably gets lower at the Avonmouth end of Lamplighters Marsh and through Avonmouth

I saw the Bristol Post report identifying Sea Mills as the location of flooding and went down to see this phenomenon, getting there about thirty minutes after high tide, predicted to be about 200 mm down on the peak at about 0930. The tide was not unusual, just onto the quay, no sign that the owner of the Old Signal Station had needed to sweep mud away and the highest recent local tide mark was near the quay, no sign that water had been anywhere near the railway.

A 12.8 m tide has never stopped the trains before.

Seen from upstream - todays tide line visible on the grass.
View attachment 129644

Seen through the road bridge. The mud under the arch was probably wet yesterday, but not this morning. It is quite normal for trains to run with the tide up under this arch.
View attachment 129641

From the station crossing the highest recent tide mark can be seen beyond the trailer.
View attachment 129642
General view from the quay, todays incursion shown by the wet mud.
View attachment 129643

We seem to have a new phenomenon, like snow, that puts the railway in a catatonic trance, without anyone else noticing.

Interesting pictures. Thanks for taking and posting them.

I'd agree that there appears to be no risk of the track being flooded. Perhaps all the recent landslips have made Network Rail cautious about damage to the embankment??

 

[sleepy_hollow]

I did wonder it the bridge was getting worse or had been reassessed, in which case there will be a need for major repairs or closure of the branch.

 

[tiptoptaff]

Waiting for divers to inspect the bridge, or so I'm informed (as the driver of the stranded unit at Avonmouth waiting to come back to BTM)

 

[sleepy_hollow]

Have you been told why divers are inspecting the bridge?

Presumably you are hoping to become 5Z74 from Avonmouth?

 

[tiptoptaff]

Have you been told why divers are inspecting the bridge?

Presumably you are hoping to become 5Z74 from Avonmouth?

Presumably as there's water under it.

I am indeed now 5Z74

 

[Dai Corner]

2K42 (1510 ex Weston-super-Mare) at Shirehampton on its way to Severn Beach according to Traksy.

 

[tiptoptaff]

2K42 (1510 ex Weston-super-Mare) at Shirehampton on its way to Severn Beach according to Traksy.

Yep, first Up beyond clifton all day. Waiting for it to get to AVN then I can head back with 5Z74

 

[louis97]

Have you been told why divers are inspecting the bridge?

That is standard procedure, typically after a closure mark has been breached and the water recedes it is required to check the structure before the line can be reopened.

 

[sleepy_hollow]

Presumably as there's water under it.
....

At this state of the tide, probably not. (The typical low tide below is from 2021/12/05)

But diving gear must be the minimum precaution to go down there.




== Doublepost prevention - post automatically merged: 23 Feb 2023 ==

That is standard procedure, typically after a closure mark has been breached and the water recedes it is required to check the structure before the line can be reopened.

Does 'Closure mark has been breached' mean 'set height exceeded'?

If the mark is about 12.9 m we shall be having repeated closures for about a month either side of every equinox.

 

[louis97]

Does 'Closure mark has been breached' mean 'set height exceeded'?

If the mark is about 12.9 m we shall be having repeated closures for about a month either side of every equinox.

Yes, unless some work is done to allow raising of the closure mark.

 

[Annetts key]

The only place on the Clifton Down to Severn Beach line that I have ever seen being at risk of being flooded by river water (sea water), is at Sea Mills.

Rainwater, that’s another matter…

In terms of the railway bridge at Sea Mills, and keep in mind that I am not a structural engineer, but this does look like the railways being far more cautious than previously. High tides in the river (it’s a river, not the sea, but I agree that it’s salt water) happen lots of times every year. That’s what happens in an area with the second highest rise and fall of the tides in the world…

Unfortunately, the railway bridge is another one that is “maintenance free” because the railway never wants to spend any money on it.

 

[sleepy_hollow]

Here, for reference is a photo showing the tidemark for that day, taken a couple of days later. Standing on the quay I can just see the side of the rails above the rubber pads on the level crossing, which suggests that the rail freeboard above the quay is about 1.7 m. Historically the highest tides of the last thirty yearshave just reached the entrance to the allotments, between the trailer and the fence.



The tide that caused the closure was about 13 m. The Hydrographic office Easy Tide service is predicting 13.1 m for the morning tide this Thursday, the 23rd. I await developments.

 

[al78]

Meteorological effects can compound tidal effects to result in a sea level significantly higher than would be expected if there was no atmosphere above the ocean.

Storm surge in the UK usually adds centimeters to the tide, so if the railway is two meters above the mean high tide height, it should stay dry. We have not had severe gales that would send a big surge up the Severn estuary. If there are strong westerly winds it is possible a large fetch up the estuary could result in wave overtopping onto the railway at peak high tide (high tides are at their highest at this time of year).

 

[sleepy_hollow]

This morning was much more like a tide:


The allotments had their flood protection in place.

The trains were not interrupted, here, the 0854 for Weston.


The closure mark emerged about half an hour after high tide. It seems that this was raised about 1 metre about a fortnight ago. It also seems that we have resumed the traditional practice of ignoring it.


The bridge will be repaired this year, replacing rusted rivets, ties, plates on both used and unused sides. Planned relife twenty five years.

 

[Taunton]

I'm sure it will be blamed on Global Warming, but there is a history of sea-river interface flooding along the Bristol Channel. The most devastating was in the year 1607, when a thousand or more were drowned in Somerset and much farmland ruined. Bit difficult to blame that one on jet planes. I remember hearing in the 1960s sheep grazing by the river near the line at Dunball (Weston to Bridgwater) were drowned.

 

[Dai Corner]

Thanks for the report. There are a number of flood warnings here on the Newport side of the Severn so I wondered if the Severn Beach line would be closed again.

I assume Network Rail have re-asessed the risk and taken a more pragmatic view.

Apparently there was a TV programme about the 1607 flood a day or two ago.

 

[Taunton]

The Environment Agency warnings appear to be a blanket one because of 'industrial action', presumably by the officers who normally monitor this. And then the railway says 'oh, it's a warning, shut it all down'.

Environment Agency Flood Warning Officers set the river or tidal levels that have triggered this message. During industrial action this message has been automatically issued based on rising river or tidal levels.

Tidal River Avon at Bristol, Pill and Shirehampton flood alert area - GOV.UK

Flooding information and advice for the area: Tidal River Avon from Sea Mills to Conham in Bristol and between the Avonmouth Bridge and Shirehampton Park including Pill and Shirehampton.

check-for-flooding.service.gov.uk

 

[The exile]

The bridge will be repaired this year, replacing rusted rivets, ties, plates on both used and unused sides. Planned relife twenty five years.

No doubt in a multi-week blockade starting two days after Portway Parkway opens