Dredging - Lowe Bure - Lack Of Maintenance

[batrabill]

3 minutes ago, BroadAmbition said:

I have watched it many times on the fish finder. Our JT recorded it in our ships log ( onboard)

He used  ‘What three words’ App

Griff

Still confused. Where is it? What What3words are you saying it is?

[FairTmiddlin]

The reference is in the left picture Drop.Warns.Memo

https://what3words.com/drop.warns.memo

[batrabill]

But the survey of the river bed doesn’t show it? 
 

Can someone explain this?

[batrabill]

Are you sure it’s not the Loch Ness Monster on his holidays?

[Vaughan]

6 minutes ago, batrabill said:

But the survey of the river bed doesn’t show it? 

That is a very small scale map.  All the same it shows the average depth in the channel to be around 5 feet.  Deeper at the outside of bends but a lot shallower on the inside, as one would expect.

No wonder the pleasure wherry Solace went hard aground around there, on her way to Oulton regatta a little while ago.

Is 5 feet deep enough, for that part of the Bure to successfully let out all this rainwater flooding?  I would think not.

[batrabill]

11 minutes ago, Vaughan said:

That is a very small scale map.  All the same it shows the average depth in the channel to be around 5 feet.  Deeper at the outside of bends but a lot shallower on the inside, as one would expect.

No wonder the pleasure wherry Solace went hard aground around there, on her way to Oulton regatta a little while ago.

Is 5 feet deep enough, for that part of the Bure to successfully let out all this rainwater flooding?  I would think not.

Ah, I’ve run aground all over the Broads. It’s a perennial hazard of sailing. 
But this thread isn’t about that. It’s about The Bure Hump. 
 

Is it unreasonable to ask where the thing is? The claim is it is affecting the whole system. 
 

If it exists, and up till now I had assumed it did then it must show up in depth surveys. Or perhaps it was having a day off when the survey boat came by. 
 

 

[BroadAmbition]

It’s not just the hump. It’s the lower section of the Bure in genera 

Griff

[batrabill]

Ah. 
 

 

Right. 

[Vaughan]

A Norfolk Wherry, "loaded down to her binns" drew at least 6ft over the slipping keel.

If those soundings are taken at MLWS then I contend the river is a lot shallower now than it always was!

 

 

This is the wherry "Gleaner" which I believe was smaller than the Albion or the Maud. The load line is the height of the side deck amidships.  Hence the saying "down to her binn irons".

Drawing scanned from "Black Sailed Traders" by Roy Clark.

[Tobster]

7 hours ago, batrabill said:

Ah, I’ve run aground all over the Broads. It’s a perennial hazard of sailing. 
But this thread isn’t about that. It’s about The Bure Hump. 
 

Is it unreasonable to ask where the thing is? The claim is it is affecting the whole system. 
 

If it exists, and up till now I had assumed it did then it must show up in depth surveys. Or perhaps it was having a day off when the survey boat came by. 
 

 

It’s the section in green on your map, I’ve  always known it as the Bure loop, my understanding was the hole section of the Bure loop not being dredged, is one of the reasons the northern river levels are generally higher these days.

[JanetAnne]

Last time my Chloe Jane went through Potter was 2012 (6'8"). That sort of clearance is rare these days though our average rainfall over the last 50 years hasn't changed that much. Sea levels have risen but again, not by the amount the water at Potter has.

However, if we do dredge the bure and manage to bring those water levels down maybe 12inches, and I am in favour of proper dredging, I still won't get under Potter.,... I will be aground long before I make the bridge!!

BA maintain navigation at 1.5m minimum at the centre of the chanel (I have that in writing from them). Take 12" off that and we will all be struggling to get near some moorings.

I've watched the dredging of Oulton Broad over the last 18 months. It was an eye opener. Seeing the wherries running aground in Oulton Dyke as they took the spoil away seemed to sum it up.

 

[Vaughan]

8 hours ago, batrabill said:

Ah, I’ve run aground all over the Broads. It’s a perennial hazard of sailing. 
But this thread isn’t about that. It’s about The Bure Hump.

Here, you have pinpointed two separate problems.

The Bure hump is more concerned with the hydraulic problem of maintaining levels during rainwater or surge flooding.

But when you talk of "sailing" : if a Norfolk wherry can no longer make passage on the main rivers (which includes modern wherries in Oulton Dyke) then that is a failure by the BA to maintain "The Navigation".

If not, what do we suppose navigation means, in this context?

[Tobster]

Is it just the river levels have risen, or is it possible that the bridge at potter has sunk on its foundations as well?

[BroadAmbition]

If that’s the case Tobster, then so have the rest of the northern Broads too

Griff

[Tobster]

11 minutes ago, BroadAmbition said:

If that’s the case Tobster, then so have the rest of the northern Broads too

Griff

My point was more to do with the bridge clearance at potter, I’m not suggesting the whole of the northern rivers are sinking.

have the general bridge clearance's changed as much at Acle, Ludham & Wroxham as they have at potter? 
with Wroxham being the furthest up river from GY it would be interesting to know how much it’s been affected over the same period of time as potter.

[dom]

My dad bought his Broom 30 from Len Hulme at LL Cruisers in Wroxham in the early 80s. At the time, Len assured us that, at extreme low tides, it was just possible to get under Wroxham bridge. That would have required clearance of at least 8ft.

Current clearance is said to be 7ft 3in on average. I doubt extreme low tides would add 9 inches, so that would suggest at least some reduction in height. Someone else may be able to suggest how much extra Spring tides affect low tide levels?

[marshman]

It takes some stretch of the imagination to see at least 8' under Wroxham even in the early '80's - others clearly think otherwise but i never remember it being anything like that in my memory back to the mid 60's.

What you hove failed to take into current thinking, is that water levels continue to rise -thats unarguable and earlier posts some time back confirm that - slowly but inexorably rather than the bridges sinking!! That was also confirmed sometime back - regular surveys are carried out and they are not moving - apparently!

Spring tides vary for many many reasons - see earlier mutitude of posts.

 I note nobody has blamed the EA - they control the dredging but I suppose that its easier to abuse JP, rightly or wrongly, as he is an easier target than Mr Philp Duffy, head of the EA

[dom]

I can remember occasions when spring tides left it looking like someone had pulled a plug out somewhere but, unfortunately, I can't put them into context to work out how big the drop would have been. I remember Caen meadow getting very low, to the point you could walk way out into the channel, but obviously very hard to tell by how much levels had dropped due to the sloping sandy beach.

If it had just been some random person saying it was possible to get under at 8ft, I'd have ignored it, but Len was a yard owner in Wroxham for some years and knew what he was about. We never quite got around to trying it and then my dad got a big nightsun type spotlight off a helicopter from somewhere (I suspect out the back door of Bond helicopters at Yarmouth!) which got fitted to the roof along with a VHF aerial, sticking an extra 6 inches or so on the air draft making it completely unrealistic.

I'm sure Connoisseurs and Sancerres used to get through the bridge with far greater ease than they do now though.

Quote

regular surveys are carried out and they are not moving - apparently!

One thing I'd love to know if how both depths on the BA surveys and bridge heights are measured, ie. how a MLW or similar datum is tracked when measuring from a vessel on a body of water which is invariably raising or lowering constantly with the tide. Presumably for depth, they must be dragging sonar, but the tide must change signifcantly over the survey length if so.

[grendel]

I tried to get the depth surveys for previous years to compare to the current ones but could not find them, I would be interested in looking at the various surveys and comparing them over the last 30 or 40 years to see if the depths have changed.

[MargeandParge]

Has the sand bar at Yarmouth still got the same depth over it or has that built up?

Kindest Regards Marge and Parge 

 

[Cheesey69]

What we need is data rather than memory. 
someone, somewhere must have recorded highs and depth and if not why not?

I suspect that the Broads is storing more water than before for longer because I’ve simply seen tides that never happened the water level largely staying the same  

I feel if it is found that the levels are rising faster than thought then the spotlight is going to zero on the fact that there isn’t much you can do about it unless you find out why.

The easiest answer is dredging and I hope that is the answer because no way will the country pay for barriers at Yarmouth or extensive canalisation away from large centres of civilisation  

 

[annv]

IIf they had a floating barrier at the new bridge to restrict the in coming tidal flow to let more water drain down to Braden then when the tide level goes down the gate/barrier would swing open letting normal flow  out. A hollow box with water in lower half to maintain it up right connected on one side with rope!!! then as incoming tide comes in the gate/barrier would swing shut restricting the in coming tidal flow. This would be cheaper than dredging and quicker there is a ship repairer close by who I'm shore could fabricate it.  John 

[Smoggy]

But a floating barrier would sort of...... float??

It would just rise with the tide and the water would still pass under, would need to be full vee gates to act as a one way valve and open again once tide dropped, for surge tide deployment only it would probably be a relatively cheap option with the new bridge as a mount point as they'd just be chained back when not required and would probably slow the flow enough even without a proper cill on the bottom to close against.

[annv]

You dont have to stop the flow just restrict it the tide pressure would hold it down against the bridge abutments until the tide changed then it would pop up and swing open. John

[dom]

1 hour ago, Cheesey69 said:

What we need is data rather than memory. 
someone, somewhere must have recorded highs and depth and if not why not?

Depths I'd imagine to be very difficult to prove without access to GIS systems that EA and similar use.

Bridge heights probably get mentioned in old guides if you could locate them. Specific to Wroxham, I don't know whether Broad Tours might have old records from when they stored trip boats upstream?