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kingfisher666

Sea Level Change, Since 1970...

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I had a chat with an old friend of mine, earlier this evening. He works for the 'Environment Agency' and had previously worked for all their predecessors, going right back to the 'Essex River Board' days, in the late 1960's.

Somehow, the conversation got round to water levels and I mentioned the often discussed 'clearance beneath Potter Heigham Bridge' subject. Without wishing to restart the 'discussion' as to the reasons for the reduced air draft beneath the bridge, he did come up with a rather startling fact (his word, not mine). That, using their measuring data, the mean rise in coastal water level around Essex (his area) has been about 120mm. (nearly 5 inches) since 1970. He added, that he wasn't in the least bit surprised, that many boats were having problems navigating beneath the old bridge and that clearance would continue to reduce too.

It does make you think, how long it will be, before the bridges at Wroxham, Beccles and Thorpe too, will become impassable for even nore broads boats. I know people will have different ideas, as to the cause of sea level rises. But, one thing seems to be certain, it is actually happening and much faster than I personally had realised. I wonder, is there anything we can do, to ameliorate the problem, or do we just accept it and carry on as we are?...

 

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well to be fair , where i am there are pictures which show the quay heading about 7-10 inches below where it was in the 1950s/60s i don't thin the land is sinking,,,;

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8 hours ago, C.Ricko said:

well to be fair , where i am there are pictures which show the quay heading about 7-10 inches below where it was in the 1950s/60s i don't thin the land is sinking,,,;

Locally the land is not but the whole of South East England is sinking as the North and Scotland rises this causes the double whammy that East Anglia is experiencing. There is hardly a glacier in the World now that is growing, most are melting at an alarming rate.

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Well, lets say for the moment that his source of information is correct, which I would think probable, that is roughly 1" per decade. This, whilst interesting, doesn't explain the "Potter Bridge Syndrome" where the average clearance has reduced dramatically over the last ten years or so.

The information does at least tend to indicate that "Climate change" is not the culprit.

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So MM you clearly have the precise figures for the situation at Potter and are able to say that over the last ten years, Potter Bridge has sunk more than that?

Or in fact are you just guessing? Methinks the latter!!!!   If not why then it is suddenly disappearing after all these years? Or has it suddenly started to sink further since the mid 80's - perhaps it something to do with the demise of the GYPHC?

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19 minutes ago, marshman said:

perhaps it something to do with the demise of the GYPHC?

Come back Charles Collier. All is forgiven!

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MM, Oh come off it :) The bridge, as far as I know, is NOT sinking. nor have I ever suggested otherwise. What I DO know is that boats which used to get under more often than not, no longer can... more often than not. Do you accept that as "fact"?

What I DO know is that Whispering Reeds boat yard now has no Hire fleet other than day-boats and Picnic boats because of the above. Do you question that one?

I also know that visitor numbers to  the pleasure boat inn are reduced because of the above. Do you question that?

My point, which  I thought I'd made clear, was that climate change appeared  not to be the culprit. I made no further observations in that post.

The complicated mathematical formulae I used to calculate that 5" in 50 years would, very approximately equate to 1" per ten years I shall not go into but only say that. those figures were provided by the Environment Agency via Kingfisher666 (see opening post)

  

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Two things have happened definitely - sea levels , and indeed river levels have risen through out Broadland.  Boats have got bigger too, both upwards and generally wider.  Almost all boats are now built out to their maximum beam  - that clearly has an impact too!

An inch is only an inch but 2" in twenty years and relative to the sharply curved arch, makes a huge difference.

But I have also spotted the subtext - takes me a bit these days but I think you would have to work a bit harder to prove that one! 

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well for what its worth, boats have got bigger, therefore they displace more water, now archimedes proved when he got in his bath and displaced an equal  volume of water to his mass, then leapt out of the bath and ran through the streets yelling eurika, that a body displaces an equal amount of water, thus it is obvious that the blame lies on all of the larger boats - they now displace more water causing the rise in water levels.

At this point I will gracefully add that I have refrained from leaping out of my bath and running through the streets yelling anything (mainly as i am sitting at my desk at work, admittedly).

(now lets see someone disprove that!)

under this theory, if all of the large boats drilled a hole in their bottoms, they would displace less water, and would once again be able to pass under Potter heigham bridge.

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I am unable to post a link at the moment but I am 99.9% certain that there is a separate Government Department to cover this problem. I believe it is "The Department of Energy and Climate Change" I remember coming across it during yet another "Potter" debate and it had loads of graphs and data on Sea Level Change, right up to the present within 2 years or so.

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there is a government review that can be found here - https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/663885/Future_of_the_sea_-_sea_level_rise.pdf

this says that the rate of rise is increasing from 1.7mm per year since 1910  to its current rate of 3.2mm per year, it does attribute 40% of the rise to climate warming - but not as you would imagine, by the melting of icecaps or any other reason but that as you warm water, it expands slightly, so 40% of the rise in levels can be accounted for by the fact the water has warmed up, so is taking up more space. (similar to a block of metal expanding as you warm it and contracting when you cool it) with only 25% of the level rise being caused by melting glaciers and ice sheets. sea ice melting contributes zero to the rise in water level, as it displaces the same amount whether in ice or water form (see my earlier post on archimedes).

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The climate is changing fact, the climate has always changed fact and it will continue to change, we may slow it down or speed it up a bit but we wont stop it and yes it will affect water levels and all aspects of life as we know it we have to accept and get used to it as a fact of life.

I have often bemoaned the fact that my boat which was built to and often did go under Potter but no longer does, not because I expect any miracle changes that would allow me to do so again but purely as a response to those that always suggest it is about choice of boat and try to tell us its all our own fault rather than a change in the environment.

Fred

 

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There is an assumption in these posts that the rise of 5 inches in fifty years has been gradual. I think if you look deeper you will find that is not the case, and that the rate of annual sea level rise in the North Sea is increasing. 

I'm interested in what people see as the cause for this rise in sea level, if climate change / global warming is not the cause.

Perhaps the rate of kelpie mituration is to blame?

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well as you heat water (above 4 degrees) it increases in volume (very slightly) but when you think there are 1.3 billion cubic km of water, that tiny percentage is converted to a small increase in sea level. so maybe with a 4 degree rise, you will get an increase in volume of the seas around the world equivalent to 32.5 million cubic km, spread over the whole world that may just be a few mm per year.

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Plus all the rubbish that's dumped in them.John

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Paul, I used to claim that lack of dredging the lower Bure was to blame for this problem, but it was pointed out that flood defences were a significant contributor. Now, it is probable that the cause is a combination of these things. Climate change may also be a factor, but in my opinion   not a major one.

That the lower Bure needs considerable dredging doesn't seem to be in doubt, it is mentioned in many threads. Further to that,  the problem seems to coincide with these defences being built, a point that does carry a great deal of weight.

However, if the whole shooting match can be put down to "Climate change" then there can be no action to be reasonably taken. What a marvellous excuse for not doing much about it.

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2 hours ago, grendel said:

well for what its worth, boats have got bigger, therefore they displace more water, now archimedes proved when he got in his bath and displaced an equal  volume of water to his mass, then leapt out of the bath and ran through the streets yelling eurika, that a body displaces an equal amount of water, thus it is obvious that the blame lies on all of the larger boats - they now displace more water causing the rise in water levels.

At the risk of being pedantic I draw the honourable member's attention to the fact that Archimedes was sitting in his bath at the time, not floating in it. Nor, hopefully, doing anything else in it as that may have altered his displacement and therefore his calculations. A floating vessel does not displace an equal amount of water : it displaces its own weight in water.

Quoting Greeks can sometimes be expensive. It's a bit like the Athens prostitute, when being disrobed by her client, who said "Euripadese, you pay for them!".

The theory of larger boats having more displacement does not "hold water" in view of the Great Estuary Theory about which our honourable and learned member Timbo will advise us. This dictates that the area known as the Broads is open to the sea and therefore subject to the rise and fall of tides.

I doubt if the increase in mean displacement tonnage of the Brundall Navy will have had any effect on the level of the North Sea but I still believe that the dredging of the lower Bure to facilitate that connection to the sea cannot be a bad idea. That way, we might at least still be able to get under Potter at low tide.

Perhaps I have been listening to too much BBC Pariament today?

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An interesting debate which I will not attempt to pretend to have any expertise on just observations, most rivers widen into an estuary or delta where they meet the sea giving a wide area for silt deposits depending on local currents, the Bure narrows as it approaches Great Yarmouth which while increasing the speed of flow also creates an upstream bottleneck that logically requires constant dredging how that does or would affect the upper reaches I have no idea.

It would be interesting if someone with the knowledge and ability could do a comparison in the changes in water levels between the Broads rivers and say the Orwell, Blackwater, Crouch, Chelmer and even possibly the Thames and Medway to establish the affect of rising sea levels on differing waterways on the East coast, hopefully this would at least give a pointer as to whether it is a general problem or if there are other issues specific to the Broads.

Fred

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However, if the whole shooting match can be put down to "Climate change" then there can be no action to be reasonably taken. What a marvellous excuse for not doing much about it.

And we all know just what 'Responsible' body has been using that very marvellous excuse ever since they came into being now don't we? (Do try to keep up and pay attention at the back)

'B.A' was designed to go under all Broads Bridges, launched in 66, she has an absolute minimum airdraft of 6ft 4"

Ok, I can get her down to 6ft 3" but that involves removing the windscreen entirely (About half a dozen screws) which is in my skippers handbook onboard - Cheating and for emergency bridge shooting - I have never needed this extra 1" and hope I never do (Careful there Griffin)

'B.A' in the 60's / 70's / Most of the 80's regularly went through PHB as did many Brooms Admirals / Supreme Commanders we hired, they need around 7ft from memory,  it was not unusual, it was the norm during normal low tides. Then of course we lost the Gt Yarmouth Commissioners looking after the Broads and the Broads Authority came into being (88?).  The lower Bure ceased to have year round dredging, PHB became less of the norm and more of a treat / special occasion.  Nowadays its a couple of times a year if we are lucky enough to be afloat near to Potter when we get an exceptionally low tide on the Northern rivers.  'Weather' (Pun intended) that is solely down to climate change or purely a coincidence when the Blessed Authority stopped dredging - Erm you decide, How long do you want - More than a couple of seconds? - Really?

Griff

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Griff, That had been my view for quite a while but various folk told me not to forget the flood protection work. This too played a significant role. I have conceded that point and in fairness said work was much needed.

It remains to be seen if or how the BA might deal with this problem, the question of whether or not thorough dredging of the Bure from Breydon's yellow post to the Pleasure Boat dyke would cure it. still needs answering. All in all it's not as straight forwards as I first thought, but I still believe it would help.

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As regards bridge heights Potter, Wroxham and Beecles etc may be iffy in the future if levels continue to rise What about fitting ballast tanks to future cruisers like a  submarine (Not so drastic of course) but enough to lower the craft just enough to get under the bridge then a rapid pump out and back on your way, no idea how practical this would be but unless something is found the Broads range could shrink to most boats eventually.

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I have one little question, about the proposed solution of dredging the lower Bure. If dredging allows more water to exit the northern rivers (Bure, Ant and Thurne) as the tide falls, then surely, when the tide rises more water will be able to flow up those same rivers, thus negating any advantage gained?...

I admit, I know absolutely nothing about tide and hydrology, but if more water comes into the system (as well as leaves). Wouldn't those homes and business properties around Horning Ferry, which occasionally suffer flooding now, be more often affected and might not the lower Thurne riverside properties be more at risk too?.

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48 minutes ago, kingfisher666 said:

I have one little question, about the proposed solution of dredging the lower Bure. If dredging allows more water to exit the northern rivers (Bure, Ant and Thurne) as the tide falls, then surely, when the tide rises more water will be able to flow up those same rivers, thus negating any advantage gained?...

I think the main answer to that is that the ebb is always stronger than the flood as the Broads rivers have headwaters. So there is a constant flow of water coming down into the system regardless of what the tide is doing. There is more volume in the Yare and Waveney, which (they say) is why the tide turns on Breydon an hour before it turns up the Bure although I have never been quite sure about that one.

Going by my own memory of the days when the Commissioners were dredging regularly, I don't think there was any more flooding of places like Horning or Wroxham than there is now. I would think it was probably less although I think the spring tides in Thorpe were higher then than now. Remember that towns like Reedham, Acle, Stokesby and St Olaves all have high flood banks now, which they never needed before and I think this is because the grazing marshes are no longer being used as washlands to absorb the flood tides.

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Good point Andrew (Kingfisher666) but as I understand it, and I stand to be corrected, the thorough dredging would bring back the full range of the tide giving the lower water at low tide. Again as I understand it there would be little change in the high tide level, though I don't fully understand why.

Now, I have a question for those with thorough knowledge of the southern waters. Weknow that over 7' clearance was common at Potter. now it is the exception rather than the rule. Has the same phenomenon been witnessed at Beccles old bridge? Second question, what does the BA's tide table give as the clearance at both bridges and is that figure often achieved? 

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