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The Norfolk Broads Forum / General Chat / Ludham Bridge Heights
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Posted By Discussion Topic: Ludham Bridge Heights

Similar Threads That Might Help :
Ludham Bridge Height Gauges| Ludham Bridge Height| height gauge ludham bridge| Bridge heights| Bridge Heights On Camera ?|

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Strowager
Mar-11-2012 @ 9:03 PM                           Permalink
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Mardles sometimes
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I know it's not arched, like Wroxham and Potter, but the actual clearance under Ludham bridge has always intrigued me as well, so I've done another forum "photo" survey.

Same group evolved technique as before, square on, from some distance away, with a telephoto lens and high resolution full frame DSLR.

It's actually quite tricky to summate the results, because the bridge tilts from side to side and also along it's length. Couple that with the 25mm difference in the BA gauge readings, and it needs some studying.

The bottom line is that the gauges are actually pretty close, if one takes the centre line, lowest side.

I couldn't give a cross reference to the EA river level datum this time, as the Barton Broad ones seems to be offline, and the Ranworth Broad one is stuck at 4 am this morning...

Usually caveats apply, no liability implied or accepted.  Tinhat




This message was edited by Strowager on Mar-11-12 @ 8:05 PM


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ADI
Mar-11-2012 @ 10:23 PM                           Permalink
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Excellent work strow, saved to my pics as werte the other two, hope the authority dont adjust the marker boards, bet you dont fancy doing beccles old bridge, that would be very useful to lots as the CinC is going up that way August bank.

Regards

Adi, Michelle, Beck and Braydon,
the crew of FERZAN.

Torty
Mar-11-2012 @ 11:16 PM                           Permalink
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My rough calculation from Strow's data is that the air drafts given by the gauges is within 2 or 3%, which isn't bad. Depending on the flow through the bridge, which can be quite fast at Ludham (I have paddled keelboats through there on a number of occasions and going with the current is definitely preferable to going against the current), it is quite likely for one gauge to read one or two inches different to the other one.

Having hit Potter on one occasion, resulting in significant expense and greater loss of face, I am grateful for a margin of safety.

Phil

Strowager
Mar-12-2012 @ 10:46 AM                           Permalink
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Adi - Yes, the possibility of the marker boards moving (either by the BA or damage) is a problem, as it could throw the comparative height factors out considerably. Beccles old Bridge, more of a challenge, as you say, though not impossible, with the much gentler arch profile. Maybe when I'm next down there...

Torty - Yes, I'd heard about the damming effect of the bridge constriction varying the levels, so I purposely took the downstream photos at slack water on the morning low tide, and the upstream photos at slack water on the afternoon high tide. There was no perceivable current on the surface, and both gauges showed the same 25mm difference.


I checked the Environment Agency's river level website again this morning, and yesterdays detailed data is now there, so it appears that they upload the graph every 24 hours.  This has given the opportunity of an accurate comparison to bridge gauges, so now anyone can remotely know the height of the downstream bridge gauge by going to the EA website at http://www.environment-agency.gov.uk/homeandleisure/floods/riverlevels/120738.aspx?stationId=6215 which gives the nearest monitoring station to Ludham Bridge (Ranworth Broad).

Subtract that EA level "above datum" from 2.90 metres, and you should have the downstream bridge gauge height....


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robster
May-07-2013 @ 1:30 PM                           Permalink
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I found this thread, and was wondering if the height markers and this info is still current?

The reason I ask is that I am out on Superior Light in a few weeks and wondered if I can pass under Ludham Bridge - the air draft i 8'5" and HW publishing a minimum bridge height of 8'6" (2590mm). I know heights will change daily, but according to the EA website, a height of 220mm is showing, subtracted from 2900, this gives a height of 2,680mm, meaning a clearance of 100mm...correct?

Plus, Mrs Robster is becoming a little porky of late, so that might help....  Wink

ranworthbreeze
May-07-2013 @ 1:43 PM                           Permalink
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Hello Robster,

I hope Mrs Robster was not looking over your shoulder or you will be in trouble.

8 ft 5inches could be a problem if we get rain. I have known people whose mooring are above the bridge and have been unable to get back to them for several days if there is bad weather. As far as I am aware there is a difference in the hight boards by up to 2 to 3 inches from one side of the bridge to the other.

Being stuck above bridge can be very costly so I would check all the options before commiting passing through the bridge.

Regards
Alan

Alan Hood
Ranworth Breeze Boat Syndicate
www.ranworthbreeze.co.uk

steve
May-07-2013 @ 5:16 PM                           Permalink
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hi there ,
i'd ring the boatyard to get more info on this , and having just looked at your hirecraft the only bridges they state it won't fit it is
"Please Note!

Superior Light will not pass under Beccles Old, Potter Heigham or Wroxham bridges."
so it will fit under ludham bridge , so again i'd ring the boatyard for more info and also if your still not sure ,im sure our jason and staff (sos24/7)at ludham bridge boatyard would be also happy help you on your day you wish to go through the bridge ,



steve and vicky

Pete
Oct-03-2015 @ 11:07 AM                           Permalink
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The difference in the gauges is probably down to bridge hydraulics.

When water flows through a narrow bridge like at Ludham it is constricted. The water level is increased upstream of the constriction for a short distance and drawn down on the downstream side.

Of course the gauges themselves may also be incorrectly sited.

Pete  



This message was edited by Pete on Oct-3-15 @ 11:08 AM

rustic
Oct-03-2015 @ 12:51 PM                           Permalink
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There will be approz 4 slack waters during the day, under the bridge, two at their highest, and two at their lowest, so approx. every  6 1/4 hours, a comparison can be made to see if there is a difference between the gauges.
I'm sure there will be a difference.

The wind and air pressure changes also plays a big part in predicted high and low tides, both in their range and their timing.

best regards, Richard.

Can't wait to be back on our boat on
the Broads.

annville
Oct-03-2015 @ 4:44 PM                           Permalink
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And don't forget that if you go through against the tide with a large hull to slowly, the water pressure will raise  the boat higher out of the water and if you go with full throttle the opposite will happen you will dig the water from under the boat one of the reasons pilots go through bridges on full throttle. John

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