Potter Heigham Bridge

[SPEEDTRIPLE]

One thing people are forgetting is the BEAM of all modern boats is usually 12ft, whereas 50ish years back, most were a mere 10ft 6ins, and that`s a 40 footer. Wroxham and Beccles have wide spans, Potter is a very narrow span, so the "archway" may be higher than the highest point on your coachroof, but the overal width of the coachroof may be too wide.  A lot of modern Broads design, and even many from the 70s have a cutaway at the edges of the coachroof, and a slight arch into the main part to allow for clearance.   I do agree the dredging issue, but for ALL the broads, and i also remember seeing somewhere (can`t remember where) that a university study many years ago proved the bridge foundations at Potter ARE gradually sinking, because of the sheer increase or the average weight of the vehicles that drives over it, unlike the horses and carts of 600 years ago.

[expilot]

6 hours ago, ChrisB said:

I remember 6ft 8ins being quoted by BA and that reduced to 6ft 6ins about 6 years ago never seen 7ft 6ins.

Ex-Pilot where are you?

I started my piloting career at PHB in 1988 and continued until 1999.  In all those years I didn't once see 7' 10" at LW (It would have been 7 feet 10 inches at LW if it were 7' 6" at High).  We considered ourselves very lucky to see 7' 3" - and then only very rarely - at LW.  In those days, about two thirds of the hire fleet would get through the bridge at average LW.  We would put anywhere between 10,000 and 15,000 boats through per Easter to October season.  I doubt if this year, the total will be more than 1,000 - and many of those will be day/picnic boats.

I don't know if it is my imagination, but I sense that, since the limited dredging on the Bure, the tidal flow has increased, but the tidal range remains at 4" daily rise and fall.

9 hours ago, grendel said:

I seem to recall Expilot saying that there would be more clearance if the river bed under the bridge were dredged.

The idea of dredging beneath the bridge to increase air draft was very much tongue in cheek.  Apart from anything else, the arch has a solid horizontal base not that far beneath he water surface.

 

[JanetAnne]

Hickling is now so shallow in some areas that, should the flow be reinstated properly in the lower bure,  large areas of Hicking Broad could become land again!

There has been no significant increase in yearly rainfall over the last 50 years for Broadland - google it... The only change is the way it rains with more extreme weather.

The BA are required, by law, to maintain navigation. In Dr Packman's own words 'a depth of between 1.5 and 3.0 metres' is maintaining navigation.

 

[ChrisB]

6 hours ago, JanetAnne said:

Hickling is now so shallow in some areas that, should the flow be reinstated properly in the lower bure,  large areas of Hicking Broad could become land again!

There has been no significant increase in yearly rainfall over the last 50 years for Broadland - google it... The only change is the way it rains with more extreme weather.

The BA are required, by law, to maintain navigation. In Dr Packman's own words 'a depth of between 1.5 and 3.0 metres' is maintaining navigation.

 

I have always thought that, when "Bypass Channel" has been mooted. The constriction caused by the bridge must hold a lot of water back in Hickling.

I am told that Natural Hydrodynamics is a very complex subject and that there are many cases of what appears a simple cure can make maters worse for no apparent reason. 

There has been controversy, for example in Poole, where the increased dredging of the shipping approach channel was said to improve depth in the rest of the harbour. Many of the sailing clubs are saying the reverse is true.

[MauriceMynah]

37 minutes ago, ChrisB said:

I have always thought that, when "Bypass Channel" has been mooted. The constriction caused by the bridge must hold a lot of water back in Hickling.

Yes ChrisB I too have wondered about that and have a possible solution. If you look at the lock on Oulton Broad, it caters for the water level to be higher at either side. One of those installed on the bypass would achieve two things. Firstly it would mean that that the ebb and flow would not be significantly changed, and secondly, if operated by the bridge pilot, a charge could be levied on boats going through keeping their income stable. 

[Ray]

A lock? There's an idea! 

[Hylander]

2 hours ago, ChrisB said:

I have always thought that, when "Bypass Channel" has been mooted. The constriction caused by the bridge must hold a lot of water back in Hickling.

I am told that Natural Hydrodynamics is a very complex subject and that there are many cases of what appears a simple cure can make maters worse for no apparent reason. 

There has been controversy, for example in Poole, where the increased dredging of the shipping approach channel was said to improve depth in the rest of the harbour. Many of the sailing clubs are saying the reverse is true.

Some parts of Poole Harbour of so shallow you can stand up there and the water comes to about your knees.     We were on a day boat years ago and suddenly realised that the Wind Surfers were standing beside their windsurfers and we were close to running aground.

[Hylander]

10 hours ago, expilot said:

I doubt if this year, the total will be more than 1,000 - and many of those will be day/picnic boats.

 

And this year has been a 'bumper' year.     Loads more happy holiday makers able to see the upper parts of the Broads.

[BroadAmbition]

Just had a glance at he current small bright blue booklet produced for the Broads Authority,   'Broads Tide Tables' 1 April 2018 - 31 March 2019.  Inside there is a page on Broads Bridges listed by the rivers they span, they list 29 bridges.  The clearances are stated as being at normal high tide during the summer.  For Potter Heigham Old (As it is listed) it states 6ft 6" at normal high tide.  So it goes without saying that low tide the clearance will be greater.

Just who are they kidding?  6ft 6" clearance at HIGH tide? - if only.  If that was the case I could get 'B.A' through at any state of tide all summer long

Griff

[webntweb]

Hamilton's charts for 1963 show clearance AHW at Potter as 7ft - at the centre of the arch.

Attached is scan of the intro page to 1963 edition (published August 62).

As you can see there has been an amendment sticker attached which states the clearance is now 6ft 8in . . . Due to recent subsidence and other causes (whatever they may be).

If a respected authority such as Hamilton's makes such a statement regarding subsidence shouldn't we presume they got their information from an official source (BA's predecessors?) and shouldn't we also expect the present navigation authority to restore the bridge clearance to its previous level; and as that would be very expensive perhaps they could add another foot while they are at it . . . 

[MauriceMynah]

Ahh, Griff, Thank you, it was 6' 6" not 7' 6". I did say my memory was pretty fickle.

Webntweb, the height guides are not taken from the top of the span. I don't know about the BA Tide table.

I wonder which would be cheaper. A canal from near Phoenix day boats round to the sheds between the two bridges including a lock to keep ebb and flow as is, and a swing/lift bridge, or even a standard bridge the same height as the main road bridge. or regular dredging of the whole river Thurne and the Bure from Thurne mouth to Breydon Water.

As it seems possible that the flood alleviation works has impacted the situation, perhaps other Government departments may be obliged to 'chip in'.

Yes yes yes, I know, I'm in Walter Mitty mode here, but it's worth a thought. Said canal would re-instate the navigation to those who used to be able to go through without massively altering the character of the area. It will be much cheaper to have it re-join the main river between the two existing bridges, rather than have two bridges on the canal.

It might even be possible to close the road that goes over Old Potter Bridge permanently so no bridge over the canal would be needed. That would help preserve the old bridge as well. Now, there's a thought!!!

[BroadAmbition]

I wonder which would be cheaper. A canal from near Phoenix day boats round to the sheds between the two bridges including a lock to keep ebb and flow as is, and a swing/lift bridge, or even a standard bridge the same height as the main road bridge. or regular dredging of the whole river Thurne and the Bure from Thurne mouth to Breydon Water.

IMHO - Most cost effective would be dredge the lower Bure, especially on the corners, + through from Marina Keys to the infamous yellow post.  Just like the Port Commissioners  used to.  This would get rid of those navigation posts on the Bure that seem to increase further up stream with less chance of grounding as has been happening.  The actual ebb / flow speed would reduce back to what it used to be and best of all? the tidal range at PHB would increase giving us back the headroom we used to enjoy from years past.  But the cynic in me says the Broads authority know this only too well and it would reveal just how shallow parts of the northern Broads have become through lack of maintenance / dredging

Griff

[ChrisB]

As I said, I have always thought 6ft 8ins until 5 or 6 years ago when the BA tables suddenly stated 6ft 6ins.

[ChrisB]

It would not be just down to the BA of course. Any "Cure" would have to go to consultation and apart from objections from the public, Natural England, NWT, RSPB, National Trust and Uncle Tom Cobbly would all have a say. It is a non starter.

Dredging is the only hope in my opinion as Griff says.

[BroadAmbition]

Agreed and if the BA were honest and up to date then they need to 'suddenly' change the headroom listed to what today's average headroom actually is at HW.     6ft 6" it is most definitely not

Griff

[MauriceMynah]

Yes, but what if... and it's a big "what if" the dredging is not the sole cause of the problem and that the flood alleviation played a far more significant part in causing this problem? 

[webntweb]

Hamilton's 1963 tide computer.

It shows rise and fall average summer springs at Potter Heigham as 1ft 3ins. Surely that can't be correct?

Roy

[annv]

Or they could just pull a plow behind a boat on a ebb tide the flow would take the mud away and dump t out to sea. John

[ChrisB]

37 minutes ago, webntweb said:

Hamilton's 1963 tide computer.

It shows rise and fall average summer springs at Potter Heigham as 1ft 3ins. Surely that can't be correct?

Roy

55 years ago. Finding someone who was old enough to take proper notice of the tidal range and confirm yey or ney could prove difficult.

[BroadAmbition]

How about this then? - Copied from another thread:-

 

 

For those of us that can cast our minds back to the sixties and seventies when the then Gt Yarmouth Port commissioners looked after the Broads, (Six staff in the office - Dozens out on the rivers) there were a pair of large tracked cranes on each side of the Bure below Acle Bridge.  They were there all year round on permanent duties of dredging the Lower Bure.  The method used was the time honoured grab bucket and chuckit onto the bank system.  The cranes did not operate 365 days a year but some of it and they were on station ready to commence action, they especially concentrated on the bends of the rivers. Hardly did one see a barge to transport the mud to another location.

Now the above paragraph is not my opinion, it is not a theory it is plain and simple fact, one countless visitors and locals have witnessed and accepted as the norm

 

Over the years I have talked to quite a few genuine 'Broadsmen' (And yes sometimes Women too) that work and live around the Thurne / Bure system.  They have been on and around the water for decades, not just a few years.  They tell me that in those days passage under Potter Heigham bridge was the norm and only exceptionally high tides stopped craft from making the passage. Indeed the two side arches used to be boarded up to deter attempts from dinghys and the like attempting using the side arches.

This also is not my opinion, it is not a theory it is plain and simple fact one countless visitors and locals have witnessed and accepted as the norm

 

Then the Blessed Authority came into being.  The two regular crane dredgers disappeared  from their normal work stations.  Slowly but surely over the years the Lower Bure has silted up, especially on the corners.  You can witness this with your own eyes

This also is not my opinion, it is not a theory it is plain and simple fact one countless visitors and locals have witnessed and sadly had to accept as the norm

 

It's a 'happy coincidence' for the Blessed Authority that the then fairly new topic of global warming and rising sea levels came to their rescue.  Now they could and did and still do blame less head room at PHB on rising sea levels, this in their eyes 'Gets them off the hook' with regards to dredging the Lower Bure.  But because we have lost the power of the system being flushed out strongly enough like it used to do we witness silting in places like Hickling Broad, and even more so in GYA, even opposite the yellow posts and that hardly ever used to happen. Coastal ships used to moor there regular.

Those 'Broadsmen / Ladies' I mentioned earlier state it is not rockets science, dredge the Lower Bure and the balance that the northern Broads enjoyed for decades will return.  I for one agree with them.  And here's a thought.  Why not just dredge the Lower Bure, silted bends, Marina Keys, under the two bridges and opposite the yellow posts just the once.  Do it properly.  Then if it doesn't have a positive effect on the Upper Bure / Thurne, those Broadsmen will go and eat their hats and I'll join them.

Oh but hang on a moment, the cynic in me shouts that the Blessed Authority know full well what will happen if the Lower Bure is cleaned out, it will show up shallow water all over the Northerns that they should have been maintaining way before now and expose them to howls of complaints and derision from owners / hirers, anglers, Local dwellers, businesses etc etc -  the whole shooting match and the Blessed Authority does not want that, they could not stand the heat.  The last thing they want is to act on maintaining what we have.  Nope, they want expensive follies like that proposed at Acle that the good Dr P. can have his name on a brass nameplate for time immemorially (Big Word)

There are still some that say, even possibly believe that ceasing of regular dredging of the Lower Bure is no proof of higher river levels at PHB.

Incredulously they even state there is no proof that ceasing of regular dredging of the lower Bure reducing the scavenging effect has caused the silting at Marina Keys, and down to the yellow post turning area.

However to add balance - There are still some that believe that a pair of Penguins walked from Antarctica to the middle east to board an Ark too, not to mention the flat earth society that meets every year travelling from around the globe

 

Here's the killer question for those who think / believe dredging the Lower Bure will have no positive impact on the Upper Bure / Thurne systems:-

Why did the Gya Port Commissioners spend year after year after year with dredgers on site ready to go when silting started to occur on the Lower Bure especially on the bends.  Just why did they do that if it would have had no positive impact?  If there was no positive impact over the years and years of experience / knowledge gained they would have stopped doing it would they not?

Your Honour - My case is rested !

 

Griff

 

 

[MauriceMynah]

And a case well put sir, but I still have to ask a few questions. (to anybody or everybody who knows the answers)

1.  You still seem to be ignoring the flood alleviation works. Is there a reason for that?

2.  When were those flood alleviation works done?

3.   Was the reduced height at Potter Heigham sudden or gradual ?

4.   When did that reduction seem to start ?

5.   Is there a definite correlation of the bridge clearance reduction to both or either event?

6. Who was responsible (Which Government Dept.) for having the flood alleviation work done?

7.  When did the BA take over the relevant dredging responsibilities?

8.   We have concluded that climate change is not responsible. Are there any other possibilities?

9.   In the late 90s and early 2000s We would regularly have the pilot take Royall Ambassador under. What clearance did that boat need?

10  And finally (for now) How often have the chalets up river of the bridge been flooded in the last 18 years? 

[Guest]

1 hour ago, BroadAmbition said:

Your Honour - My case is rested !

Griff

So your case for the efficasy of 'lower Bure dredging', is the copied hearsay of some unnamed "Broadsmen & Women'...

His (or Her) Honour might well ask, but where is the hydrological evidence?. Hearsay, is all very well, but before spending a huge amount of money on what could be a pointless project, you must have scientific evidence, that the proposed dredging will have the required results.

If it didn't work, 'eating your hat' wouldn't unfortunately return the tens or even hundreds of thousands of pounds, wasted on the project...

[ChrisB]

I do tend to agree with MM re Flood Alleviaton. Perhaps it is a combination of higher river banks funnelling water up the system and lack of dredging not letting it out again. Remember the old moorings at Fleet Dyke? They were always under water. How Hill was raised considerably. Certainly over the last 15 years I have noticed a difference in the tidal flow at Ludham Bridge which used to be notorius for flooding over the fields. Whether as has been suggested  "Plough Dredging" would work I don't know. The river can certainly get a move on during the ebb so it should. However then there is the question of where it ends up? A Bar at the entrance to the Harbour? So back to the Backhoe dredger and spoil to get rid of.

[grendel]

Perhaps we should all take to dragging a length of chain behind the boat as we navigate the lower Bure, would the additional fuel used  and diesel emissions generated lead to an overall improvement of matters and or alleviate the shallows on the corners? who knows unless it is tried. 

All we really know was that in years gone by the dredging was utilised to keep the navigation clear,  would it return the navigation to as it was, or have the other changes over the years changed the parameters enough so that it would no longer work. and as mentioned above would it just move the issue to another spot on the waterway.

[High6]

Be interesting to find out if the changes in tidal range at PH reflect to any extent what has happened to HWL at Gt Yarmouth over the years.