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smitch6

Southern Broads Extremely Low :o

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MM - I think the following post to yours answers the question very well. I am not actually against dredging per se at all, merely that I am somewhat sceptical to say the least, that more dredging lower down the Bure would have any impact at Potter, and indeed could have the opposite effect and allow more saline incursion. 

Perhaps what I would say is that the BA has been dredging the Lower Bure for several winters and I have not been able to see any real difference. The evidence of last weekend however would appear to suggest that when it wants to go , it can, so what would be the point of further dredging, more especially if there would seem to be little evidence that it would change anything?

I admit I am not a hydrologist so I don't really know, but equally the same applies to those many proponents of more dredging in that area. What I do believe however is that you cannot do these things without being certain of the consequences, as usually doing one thing impacts another - better the devil you know than introducing a whole new element no one envisaged at all.

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1 hour ago, grendel said:

is that not just the local equivalent of the severn bore?, where the incoming tide and the outflowing river meet? or is it some other phenomenon?

Not in my opinion, since the Severn bore is a tidal wave which flows up the river with the rising tide and reacts against the constant flow downstream of the river, from its headwaters. It also has to do with the funnel shape of the estuary.

What I am describing in Yarmouth is a straight line (almost dead straight) which goes diagonally across the Yare and stays in the same place all the time. When the wind is blowing there are waves, so you cannot see it but on a calm day there is a step up of about a hand's width and it goes right across the river, over to Cobham Island. Lasts for about half an hour.

It is said that this is because there is more volume of water in the Yare and Waveney than there is in the Bure, but I have never been able to quite work that one out in my mind.

One thing is now certain:

In the last couple of days the water went down in the North Sea and sure enough, the water on the northern Broads went out with it. With no hesitation. So maybe all our favourite theories about mean water levels have just flowed out to sea as well?

Maybe it really is mainly driven by a gradual change in sea level?

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11 minutes ago, marshman said:

so what would be the point of further dredging

my point is that dredging should be continued to maintain enough depth for navigation purposes, for example on shallow bends where silt has been deposited.

 

4 minutes ago, Vaughan said:

In the last couple of days the water went down in the North Sea and sure enough, the water on the northern Broads went out with it. With no hesitation. So maybe all our favourite theories about mean water levels have just flowed out with it?

it has certainly made me revisit my thinking on the matter.

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BUT - IF the 'Hump' in the Bure and the LOWER Bure was dredged, especially on the corners right down to the yellow post, done properly to the banks, then surely even more water would have ebbed out from the Northern rivers. Then during normal tidal range the levels at PHB would be averagely lower just like they used to be when the lower Bure was maintained correctly.  The southern rivers seemed to lose far more water a lot quicker than the northern rivers did.  Of course the Southern rivers don't have a restriction called the lower Bure.  And I keep coming back to this one.  If dredging the lower Bure allowing more water to flow freely would not have any great impact, just why oh why did the GYA Port Commissionaire spend so much time and effort maintaining it for so many years? And why oh why was PHB accessed as per the norm? - Coincidence? Then just by coincidence when the Ba came into being the river silted up slowly but surely along with increased water levels at PHB.  The cynic in me thinks that the Ba are allowing this to happen to save them from dredging the areas that they should have been doing before now all over the northern side.  As for climate change and increased water levels to blame - That one holds no water with me (Pun intended) otherwise the whole of the Southern side would be higher too

Griff

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surely Griff if you dredge the river, the water will flow out quicker, but will also flow back in quicker, and will still be dependent on the water level at Breydon, I can see the case being made by the non dredgers, that if the flow was clearer, then salt water incursion would be worse. we have clearly seen over the weekend that the river level can drop rapidly, but only when the sea level in the north sea also drops, so I am afraid my mind has been changed - by mother nature. I would still advocate dredging to keep the navigation clear across the width of the rivers and on the bends, but I no longer think this would drop the river levels to the extent we had supposed. 

seeing the effects of the low water at Brundall and other places where most of the boats were aground, I am thankful in a small way that this tidal range isnt seen as badly on the northern rivers. 

I do wonder what the levels were like above Potter Heigham Bridge over the weekend, for instance was hickling broad still navigable, what variation was there due to the low tides at that location. 

I like some others am beginning to think this is far more complex than we supposed, and that there isnt a simple fix that wont make matters worse in some respect or other, somewhere.

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What we need is dam across the bure and Yare to stop the sea levels affecting things . Paid for bybthe EA. With a lock for boat access.

wont help the bridge heights at potter though, but might negate the need for dredging.

of course the lock would break after 6 months so the BA could then save money manning it and save on the dredging. 

More money for leccy posts or moorings? Or PR campaigns to promote our beloved National Park :default_beerchug:

this is a sarcastic comment  :default_icon_bowdown:

 

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So Griff - can you back up your claim that the GYPHC actually took away more silt than the BA are currently removing?

Methinks not so lets not, with respect, keep on banging on about it - that was over 30 yrs ago and in todays world is pretty meaningless.  The BA has been down there over the last few years taking away the inside of some of the bends - in my early days in cruisers in the late 60's there were plenty of bends where the inside was shallow, as it is now at certain stages of the tides.

But what we do now know thanks to Deidre and to the North Sea temporarily b*ggering of for a bit, is that the theory about the Lower Bure is rather dented - nothing certain but a little bit less believable! And yes Hickling is well down today - probably by at least a foot or so still from this time last week and if you look at the following link you will see that it is today actually well off the bottom it reached Sat night, yet is still well down. It would appear that not even Potter Bridge proved to be the impediment some believed it actually is -  another theory busted to some extent by dear old Deidre perhaps??

 

https://flood-warning-information.service.gov.uk/station/6210

 

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Now this is interesting

REPPS:

https://flood-warning-information.service.gov.uk/station/6217

The Repps area did not see the same profile of drop and rise as Hickling and Acle

ACLE:

https://flood-warning-information.service.gov.uk/station/6203

So, to very amateur eyes like mine, the level at Potter is more static and not as sensitive to outside effects as Acle below it (perhaps not surprising) but also, (more surprisingly) Hickling above it.

Or am I misreading the scales ???

 

 

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Is the river at PH staying up because hickling is emptying through it? And does that end drain through the land direct to sea by much?

Just questions, I know nowt!

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7 minutes ago, Smoggy said:

Is the river at PH staying up because hickling is emptying through it? And does that end drain through the land direct to sea by much?

Just questions, I know nowt!

Centuries ago, or maybe even millenia, the original outfall to the North Sea was the old hundred river, via Potter Heigham and Martham Broad. So it`s quite feasable that the water levels emptied through there?.

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To me it looks like Potter and Repps (perhaps not just the bridge but the whole section) are a bottleneck???

It would be lovely if someone who really understands this stuff would contribute. BESL??

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I`ve just looked on Google sattelite view, and you can clearly see the original coarse of what was the old hundred river, now the Thurne,  going past the northern side of Martham Broad, and its original coarse meandering North Easterly out to sea, though over many centuries, things have changed dramatically, probably by mans interference. In fact, i can remember the old maps of the Broads used to have it marked out on them.

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2 hours ago, batrabill said:

So, to very amateur eyes like mine, the level at Potter is more static and not as sensitive to outside effects as Acle below it (perhaps not surprising) but also, (more surprisingly) Hickling above it.

to me the repps gauge looks like the sensor bottomed out at just over 0.2m - mainly because where all the other graphs carry on dipping, that one just levels out and shows almost flat over a wide period.

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Nothing goes out that way now though - its actually physically cut off from the system! Or rather there is a locked gate/sluice and beyond it a dead end. That marsh just there is one of the better reed beds and closely maintained accordingly

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So Griff - can you back up your claim that the GYPHC actually took away more silt than the BA are currently removing?

Methinks not so lets not, with respect, keep on banging on about it - that was over 30 yrs ago and in todays world is pretty meaningless.  The BA has been down there over the last few years taking away the inside of some of the bends - in my early days in cruisers in the late 60's there were plenty of bends where the inside was shallow, as it is now at certain stages of the tides.

That's a belter is that.  You sure you don't work for the Ba spin department? If not you should do.

An inconvenient truth - so lets ignore it and pretend it didn't happen.  The figures you ask for - Of course I don't know, neither do you.  What I do know from numerous eye witnessed including my own is that there were grab cranes on either bank ready to operate all year round.  It doesn't matter in today world - No of course it doesn't we can all now ignore another inconvenient truth that PHB has higher water levels than in the days of the port commissionaire so lets ignore that inconvenient truth too shall we?  Even in todays world the Ba's own tide tables booklet states an incorrect truth that clearance at PHB at summer HIGH water tide is approx 6ft 6" and we all know we are proper lucky if we see that kind of clearance at LOW water - Another inconvenient truth that the Ba bang on about.  They even state at HIGH water normal summer tide that Wroxham road bridge has approx 7ft 3" clearance.  7Ft 3"  I ask you! so what is average low water clearance 7ft 10" ??   It's beyond a joke and far from funny.  So you Marshman can stop banging on about it if you choose to do so.  I will respectfully  not turn a blind eye and ignore it.  To ignore it is pretty meaningless other than giving up on what we have left as of today.  There is nothing worse than when good men do nothing

Griff

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1 hour ago, grendel said:

to me the repps gauge looks like the sensor bottomed out at just over 0.2m - mainly because where all the other graphs carry on dipping, that one just levels out and shows almost flat over a wide period.

Yes, you may be right 

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Griff - I agree the Tide Tables and clearances and indeed the website are imprecise . No argument there.

Unlike others then, I guess you are pretty unimpressed the water did run out quite adequately this weekend? To me it suggests that there are many factors at play at any one time and that there is no guarantee that dredging would have the impact some suggest. As I said earlier, I would fear the unforeseen circumstances that may occur and I would suggest that even if the BA DID ask for permission, that approval from Natural England would not be forthcoming for that very reason. I might well be wrong!

I also think that climate change IS having an impact on sea levels generally, but like the silt issue, the impact is just impossible to assess accurately, either North or South, simply because of too many other factors involved. However the next time this dredging topic is raised, you will not be surprised that I will certainly recall what did happen Saturday night and probably either myself, and perhaps others , will remind the dredging advocates of just this fact!!!

 

 

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Unimpressed?  No I was disappointed more did not flow out but was not surprised in the least.  I would have been impressed and very surprised if the Northerns had drained out as much as the Southerns, then my dredging point of view would have been pointless and I along with plenty of Broadsmen would have had no argument but due to the bottleneck that is the lower Bure it can't flow freely enough.  Rocket science it ain't.

As for tide table and clearances being imprecise, change the imprecise word to - Bullsh1t.  Do the Ba really think regular Broads users are that stupid as to believe the Ba's spin?  I've contacted them before now on this very issue and asked them to just be honest, print the actual realtime todays world average clearance heights as they are only kidding themselves - not even an acknowledgement or reply.  My guess is they would be held responsible for it by their own booklet and don't want the embarrassment.

Richad Bassey - Keeper of MTB102 who has a Broads history as long as your arm has an ambition on his bucket list - To 'Park' MTB102 right outside Hotel Wroxham.  He is confident he can get under the bridges at low tide but the shallow Bure will stop him.  He stated that it would not have been a problem when the river was dredged properly before the Ba came along.  Hang on a minute, my grey cells seem to remember that Herbert Woods built MTB'S / Gunboats during WW2 at Potter then sailed them down to Gya for the mast / bridges to be added on t'other side of the bridges.  Can't seem to remember them running aground on the lower Bure due to lack of water depth.  Mustn't bang on about that one either, another inconvenient truth to be ignored

Griff

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Even our very own NBN bridge height gauge guide is incorrect as that states at average high water PHB is 6ft5" and Wroxham 7ft3"  It is proper misleading / wholly incorrect to newbie hirers and privateers alike

Griff

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the problem is that when working out the average, events like last weekends low water level, affect the average by increasing the clearance and skewing the result, so also the warm dry period earlier this year, when we squeezed Royal Tudor through at 6 ft 7".

has anyone been able to recalculate the clearances and averages to disprove the BA figures, I suspect if you could provide scientific proof via water level tables you might get a response.

then again what is their measurement point, are they quoting the actual clearance at the crown of the bridge, - or the clearance for a boat passing through, without clarifying where their 6 ft 5" clearance is measured to, we cannot say its wrong.

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As far as I can recall from when Strowager and Paladin did the graphs  on the arched bridges the height measurement is at a point where there is sufficient width not the apex, I doubt anyone apart from the EA would have a record of the averages but I think most of us have a good idea from how often we have been able to get through say Wroxham in the last few years.

A couple of other points that don't seem to have been recognised are that because of restriction the water level above a bridge is slightly higher than below Ludham being an example and you have both bridge and width restrictions at GY, also while the tide goes in and out the flow from the upper reaches is constant therefore backing up and  raising the water levels if it cant flow when it reaches the floodtide  regardless of sea levels and I still say the water was sucked out last week it didn`t run out as per normal.

Fred

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10 hours ago, BroadAmbition said:

Even in todays world the Ba's own tide tables booklet states an incorrect truth that clearance at PHB at summer HIGH water tide is approx 6ft 6" and we all know we are proper lucky if we see that kind of clearance at LOW water

Thank you, Griff, at least I'm not the only one who thinks these high and low water readings are ass about-face, At low water the channel down through Yarmouth seems a lot narrower than it did back in the 70s, so I would definitely agree with more dredging and I do see the logic in what Griff is saying, now where's that tin hat thingy :default_gbxhmm:

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2 hours ago, rightsaidfred said:

I still say the water was sucked out last week it didn`t run out as per normal.

A marine engineer would tell us that there is no such thing as suction. . . discuss! . . . 

There was high atmospheric pressure before the front went over though, and that may have caused a suction effect.

11 hours ago, BroadAmbition said:

my grey cells seem to remember that Herbert Woods built MTB'S / Gunboats during WW2 at Potter

Woods built mainly Fairmile Bs and at least one Fairmile D and one of their buildings is still known as the Fairmile shed. The D class were MTBs which were larger than the old gunboat Morning Flight and she drew 4 ft 6 at the bow. The Fairmile B was a displacement hull and would have drawn about 5ft. Percivals also built these at Horning but I don't think they were fully fitted out there. Think "Golden Galleon" -  She was a Fairmile B.

There was also a D Fairmile moored as a houseboat in Horning in the 60s.

So is the Bure as deep as that nowadays? The Albion seems to manage although I was told that Solace grounded in the lower Bure on her way to Oulton this year.

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Question.

Did boats ever moor at Marina Quays?

If yes, Was it available to do so at all states of the tide?

If yes, but now it is not, which of the following is true...

The tidal range is greater than it used to be.... or The water level is lower than it used to be... or The river bed is higher than it used to be.

As Vaughan has said, Discuss!

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1 minute ago, MauriceMynah said:

Question.

Did boats ever moor at Marina Quays?

If yes, Was it available to do so at all states of the tide?

If yes, but now it is not, which of the following is true...

The tidal range is greater than it used to be.... or The water level is lower than it used to be... or The river bed is higher than it used to be.

As Vaughan has said, Discuss!

I have, whilst waiting for the low  tide. Poppy draws about 3'6". 

That would have been about 12 or so years ago. Not a chance now !

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