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Potter Heigham Bridge


Hrimfaxi

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But is AHW at Gt Yarmouth recorded as having increased over the past 50 years, and is this reflected at PH? The IPCC thinks sea level will rise by about 3m this century, although in fact it's no more than an inch or two.

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5 hours ago, MauriceMynah said:

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

Have we? Why have we? Almost certainly it is a major contributing factor. The European Environment Agency report sea level increase in the North Sea averaged between 3 and 4 mm per annum between 1970 and 2015. That is a sea level rise between 5.4 and 7 inches. This is down to permanent ice melt and thermal expansion. This is bound to impact inland tidal water.

 

 

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5 hours ago, MauriceMynah said:

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? 

My two-penn'orth in answering MM's questions:

When were those flood alleviation works done?  Thurne's riverbanks were commenced in 2011

Was the reduced height at Potter Heigham sudden or gradual?  I started piloting in 1989 with reliably low bridge clearances 6'8" to 7.0" at Low Water during the Summer season.  Easters were notoriously unreliable because the full moon around which the Easter date is set did not increase the tidal range but reduced significantly the bridge clearance heights at each successive Low Water.  When I left, ten years later, the water levels had increased noticeably and have increased gradually ever since. 

Is there a definite correlation of the bridge clearance reduction to both or either event?  'Definite correlation'?  No.

Who was responsible (Which Government Dept.) for having the flood alleviation work done?  The Environment Agency formed an engineering, construction and consultancy consortium - Broadland Environmental Services Limited - comprising Bam Nuttall and the Halcrow Group.

In the late 90s and early 2000s We would regularly have the pilot take Royall Ambassador under. What clearance did that boat need?  Royall Ambassador is/was an Alpha 42 and all Alpha 42s were put through the bridge at between 6'10" and 7'0" depending on the final resting position of the cockpit sliding canopy when fully open.  I believe, from memory, there was a height difference between even the Royall Ambassadors.

And finally (for now) How often have the chalets up river of the bridge been flooded in the last 18 years?  The incidence of bungalows flooding is identical above the bridge as below it.  I know of only one bungalow that has flooded in the past eighteen years. It has flooded regularly since 1989. 

I have personally lifted more than thirty of the two hundred riverside bungalows to prevent the possibility of them being flooded.  Others have also been lifted. 

In 1993 our bungalow plot, on the Hickling bank (above the bridge), flooded to a depth of about three inches.  It hasn't totally flooded since then.  In the thirty years we have owned the  bungalow, the majority of bungalow owners have since raised the capping to their piled quay-headings by about four to six inches. Our bungalow has never flooded.  The river water remains either in the river or, occasionally, over the garden's lawns.

When BESL, Broadland Environmental Services Limited, were planning the floodbank strengthening works, we bungalow owners (as consultees via the offices of the River Thurne Tenants Association) were promised that the floodbank behind our properties would not be raised any higher than existing at the time the works began.  Over-topping locations would be preserved. 

The banks have not been raised.  The previously existing over-topping points were preserved.  New ones have since formed behind certain bungalows as the reinforced (widened) banks have settled under their own increased weight.

Sometimes we simply have to admit that what happens is simply counter-intuitive.  If science were common sense we'd all have science degrees.

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Thank you Expilot, that gives me much to think about.

We always had Royall Ambassador 2.

The fact that the change has been gradual tends to favour dredging problems over Flood alleviation works.

I had a friend (well perhaps more like an acquaintance with whom I was friendly) who had the green chalet. I think he had a boat called Speckled'un   or something like that. He was an entertainer called Mark though some knew him as "Elvis". Perhaps you know the fellow I mean mean.  When he first had his chalet, I believe he suffered from flooding problems. That would have been the early 90s.

Anyway, thanks again for your answers.

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Mark, ('Britain's best Elvis')was our next door neighbour!  His property flooded frequently before he bought it.  Rather than lift the bungalow, false floor was placed over false floor, over false floor....

I lifted his bungalow, Octagon Lodge, as he renamed it, but had to replace all floors, bearers and joists because they were all as tender as a boiled owl.  

His boat was called Speckled Hen.

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We remember 1993 floods well, we were stuck on the quiet side (we moored in wroxham in those days). We waited at west somerton and travelled up to the bridge each day to see how things were. The pilots we great and helpful. They got us through I believe August bank holiday Monday by getting people out of the pub to provide ballast. 

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MM - perhaps you have missed the obvious with the gradual rise!

Perhaps it is nothing at all to do with the dredging but more to do with melting ice, to such an extent that it is now quite common for boats to pass through the NW Passage and all along the north coast of Russia. Melting ice means more water in the sea, more water in the sea means less headroom  under Potter Bridge?

If water levels generally have not been rising, perhaps you should have sent a letter to the EA and they could have saved in excess of £20m - and lots of wild mooring spots!!!!

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10 minutes ago, marshman said:

MM - perhaps you have missed the obvious with the gradual rise!

Perhaps it is nothing at all to do with the dredging but more to do with melting ice, to such an extent that it is now quite common for boats to pass through the NW Passage and all along the north coast of Russia. Melting ice means more water in the sea, more water in the sea means less headroom  under Potter Bridge?

If water levels generally have not been rising, perhaps you should have sent a letter to the EA and they could have saved in excess of £20m - and lots of wild mooring spots!!!!

Perhaps if we all drink more tea? 

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20 hours ago, ChrisB said:

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.

I can remember! I was 16 at that time. Oh, the "swinging sixties"!

I agree with all that Expilot says and I don't think the tidal range on the upper reaches of the northern rivers has changed much at all. 4inches at Potter, it always was.

I have been following this interesting discussion and I think we need to separate the subject of flood alleviation, from the tidal range and current in the rivers.

The flood alleviation that "protects" the marshes of the lower Bure and Waveney from abnormal surge tides after storms in the northern North Sea, was done for very political agricultural reasons, so that farmers could grow arable crops. It is nothing to do with the navigation and has no effect at all on the daily rise and fall of an average tide, nor the speed of the tidal current.

What it did do, however, was to prevent those marshes from being used as washlands, to absorb all the water from a surge tide flood. So the water had to go somewhere else and it started flooding towns instead! So now we need all these new flood banks in places like Reedham, Stokesby and St Olaves, where they were never needed before. This was the first big environmental cock-up, for which we can only partly blame the Broads Authority.

But this should not affect the average tidal range between springs and neaps and nor should it explain why the "mean" water level up north has seen an overall rise. There will always be floods in bad weather, but they should not cause an overall and permanent rise in level.

It is fact, that the River Commissioners used to dredge the lower Bure much more than is done now. So the theory is that water is being held up in northern areas because it cannot get away fast enough during the time of an ebb tide. Because there is less depth in the river and therefore less volume of water can be passed.

But does this hold up in practice? I grew up in Thorpe where the average tide range is several feet and so a boatyard had to lead its life around the tides. From what I can see, the tides probably came up higher in the 50s than they do do now and yet the river Yare is now very much shallower than it was in the days of the sea-going coasters. So this seems to go against the theory.

What else might it be? Do we have more average rainfall in Norfolk now, than we used to? According to another poster, the figures say no. Also according to another poster, the sea level has risen around 7 ins in the 35 years up to 2012. Project that forward and it might now be 8 ins. Perhaps that has been enough to make the difference?

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31 minutes ago, Vaughan said:

sea level has risen around 7 ins in the 35 years up to 2012.

between 5.4 and 7 inches, in the 45 years from 1970 - 2015, but the specifics are not important.

The fact remains that the level of the North Sea is rising, and the EEA predict that the increase will continue and accelerate. They don't publish precise levels, but place each area of sea or ocean into categories, 0-1mm pa, 1-2mm pa and so on up to the highest category of 4mm+. For the first half of the 21st century they move the western part of the North Sea, that off the Norfolk coast into the highest 4mm+ category. Projecting that forward for the 35 years from 2015 - 2050 that's another 140mm of rise, another 5.5 inches plus. If that proves correct then by the time my lad is my age it is unlikely anything bigger than a rowing dinghy will be passing under the bridge. 

I do agree with Griff's comments re dredging in the Lower Bure, which I believe are making the situation worse but I also believe that no amount of dredging will restore the clearance we saw in the 1970s.

I strongly believe that the only way that access will be maintained in the years to come would be through bypassing the old road bridge, which could be done, relatively easily and I produced a design to do so many years ago, at that time as a work of folly. You would not need a lock, the design of the bypass channel is important in how hydrodynamic flow is managed especially the shape of the openings into the main river. You would require some kind of stop gate as used on the canals which could be used in time of major flood tides to prevent the bypass allowing additional flood water upriver but that could be done easily enough. 

The Causeway would be severed closing the old bridge as a through route for traffic but it would continue to provide vehicular access to Phoenix Fleet, The Chip Shop and Amusements and properties on the sheds on the Martham Bank above the bridge.

Would it ever be done? No, not in the current climate BUT! Wait a few years, wait until the holier than thou "right sort of boat" brigade, and the "I'm alright Jack, my boat goes through" clan start struggling and we might just see attitudes change. When the only boats competing on the 3RR are laser dinghies then maybe public opinion will change and pressure bought to bear. The big danger is of course that by the time that happens the ever decreasing passage under the bridge will be used as an excuse for the powers that be to close navigation on the Upper Thurne completely, succumbing to the pressure of the conservation groups.

To squeeze in a few more metaphors, the horse will have bolted whilst the ostrich still has it's head in the sand and ar*e in the air. 

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Whilst I am not doubting that the 'experts' statements regarding climate change are more often than not, made in good faith, I cannot help but believe that many such statements are used by political parties to support their own agenders, and as a result Scientists statements are cherry picked without mercy. Schoolboy physics tells me that if I float a cube of ice in a glass, as it melts, there is no change in the level of  liquid in that glass. (ref. Archimedes). Further, Schoolboy Geography tells me two things. The North polar Ice cap is floating, and that  over 70% of the Earth's surface is covered in water.

From those two (simplistic I admit) facts is it unreasonable to suggest that the increase in water levels as put forward by Government departments might be somewhat exaggerated, and therefore that the Measurement of 7" increase in water level may also be slanted.

Before people start suggesting that I'm acting like an ostrich, burying   my head in the sand, I have to ask why I should take on face value statistics, produced by organisations known for massaging figures and cherry picking the results.

We know the problem in this instance. Clearance under Potter Heigham bridge is reducing.. It seem sensible to me that the cause of the problem needs to be established before looking to remedy it.

Flood relief work had been suggested to me, so I am trying to look into it. Thus far, it looks like a diminishing likelihood. Lack of dredging has also been put forward. That is looking increasingly likely. I have brought "Climate change" i9nto the equation but fairly quickly discounted it. The diminishing clearance has been happening over the last ten years. climate change somewhat longer.

So. What else could be causing the problem. Any suggestions welcomed.

After that we should start looking into possible solutions. As far as I can see the possible options are as follows,

1,  Remove the bridge. Unlikely.

2.  Bypass the bridge, unlikely but doable

3.  Lower the water level.   Also doable and the most likely solution.

4.  Do nothing and eventually let the Hickling area become un-navigable. This would be the preferred option by the "Natural England", the RSPB and of course the BA.

But should we toll payers just sit back and let that happen?

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So if ice and accumulated snow over the land masses melts, does that not increase the level of the sea? As 12% is now covered by snow and ice and has been reducing steadily will that not have an impact?

 Equally if a large piece of a glacier which was on land falls into the sea does not that too increase the sea level? Surely there are plenty of glaciers moving towards the sea and these are introducing new water? And if the thickness of the ice on the land, such as Antarctica, is reducing will have an effect surely?

And I thought it was only Donald Trump who was in denial of climate change? Still never mind there are still well known and active members of the Flat Earth Society - each to his own!!

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There is  also the "rebound" effect on the land  as the Glacier melts. For eg Scotland  is  ever so slightly "rising" as its Highland glacier/snow cover melts relieving the weight of its  downward pressure on the crust ,  and in turn the UK tilts with the East  driven "downwards" into the sea and so getting a double whammy   !

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Very simplistic MM, and mostly wrong.

The figures for sea level rise are actual, measured levels issued by the EEA. Not estimates doctored to suit the needs of whichever political organisation has funded the research. Of course, future predictions can never be guaranteed. Sea level rise might just stop, as if by magic tomorrow. Then again I might win tonight's Euro Millions Jackpot. The European Environment Agency is a very well respected and trusted organisation. 

Your schoolboy physics teacher perhaps needed a change of career, as the glass should have contained salt water which is slightly more dense than fresh water, and even more dense than ice, as water is by some peculiar quirk the only substance on earth which gets less dense as it solidifies (I paid attention at school!) Repeat your experiment, on sufficient scale and you will see the water level rise. My 8 year old son has done this experiment in school, you'll need something bigger than a glass though. A lab tank is ideal. 

The one other point you make which seems at odds to what we have heard in this thread is your presumption that the clearance has only diminished over the last ten years. I think we have seen that it has been happening much longer than that.

Before anyone accuses me of being deliberately contrary however, there is one thing we agree on. Your final statement. 

But should we toll payers just sit back and let that happen?

In my opinion no, but then I am no longer a toll payer, so what is it to do with me?

 

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29 minutes ago, Mark said:

There is  also the "rebound" effect on the land  as the Glacier melts. For eg Scotland  is  ever so slightly "rising" as its Highland glacier/snow cover melts relieving the weight of its  downward pressure on the crust ,  and in turn the UK tilts with the East  driven "downwards" into the sea and so getting a double whammy   !

Not so, that is just the weight of the scots coming down south because it's nicer down here! (and we don't do bagpipes)

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Here's a left field idea for you. The work I suggested at Potter Heigham could be done as part of a landmark project to regenerate the area and promote tourism to the Norfolk Broads. If Navigation were to benefit then part funding from that budget would be appropriate. It could also attract private investment or sponsorship as well as funding from tourism authorities, even lottery funding. A kind of "cross organisation" project so no single budget takes the hit.

I wouldn't want to suggest what this landmark project might entail, perhaps a visitor and education centre maybe? After all, there is much more to attract visitors at Potter Heigham than at some other locations, take perhaps Acle Bridge as a random example.

It could be a CEO's golden achievement, and monument to his time in office which offers great benefit to many different broads users.

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7 minutes ago, grendel said:

The only problem with this is that according to statistics we are overdue for a further ice age.

Ah but perhaps  Anthropocene Climate change has  helped delay this ? Maybe if we ever hit Global  CO2 reductions the new ice age  will hit extra hard (by ice age standards)

 

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ah but its not called global warming any more - its just climate change - this means that it can get hotter - or colder. for example if the gulf stream ceased to flow, we would be at temperatures more experienced in Canada and Moscow- ie much colder winters.

the gulf stream is driven by the atlantic conveyor, of which reports have said it is slowing - this is a conveyor of cold water from the north atlantic running a deep cold current down to australia, which then via umpteen other ocean currents back to feed the gulf stream. climate change could change these patterns of weather inducing currents, there is evidence the atlantic conveyor has stopped before due to an influx of fresh water from the great lakes, so who knows really.

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