Meg

[Meg]

Hello

I feel in my bones this is a silly question but despite the howl you make it somehow seems logical. The tide table says for Wroxham add 4.5 hours to the time given for Gorleston high water, ok so it takes 4.5 hours for the water to travel to Wroxham, got that. Is it the same 4.5 hours for low water to occur or as it seems to me will Wroxham will be lower quicker than that!

It sounds even dafter written down, sorry.

 

 

[SwanR]

Not a daft question at all. I follow your logic but I have no idea about the answer or the science behind it.

[Bound2Please]

Hello Meg

Not so easy to put into words really. Well here goes. You get approx 2 tides a day so in theory so approx 2 high tides 2 low tides, some days 2 of one and one of the other. It takes approx 6 hours to rise and approx 6 hours for each tide to fall dependant on phase of the moon. Around the country are tables of tide constances, where you can add or subtract from a High tide at a certain place to get the hight tide some where else.

I hope that makes sense to you Meg. If not im sure one of our scientific memembers can put it better.

Charlie

[Chelsea14Ian]

Sometimes life gets interesting when the wind blows in and stops the tide from going out.We have seen this happen a few times over the years.

Ian 

[NorfolkNog]

This is a good site for information about tides and goes into more detail. 

The tide tables are excellent IMHO, we always print them off before each trip. 

 

http://www.norfolk-broads.org/index.htm

(click on the tides link, top left) 

[ranworthbreeze]

Hi Meg,

The tide table that Howard has given in the post above is the Shorebase table which is among the ones we have listed in our tide tables, personally I use the Broads Authority table because it gives us the height at low water which is relevant to us for passing through Yarmouth.

You can look at all of our listed tide tables which is in the Handy Information tab at the top of the screen.  Here a link to the tide tables:-

http://forum.norfolkbroadsnetwork.com/handy-information/tide-tables/

Regards

Alan

[MauriceMynah]

I'm not sure that the "tide tables" are giving Meg the information he is asking here, but more " what is actually happening to the water throughout the cycle?" and I suspect, a bit like Meg, I have wondered the same and how best to phrase the question?

The problem I'm having is that I'm still to work out how to phrase the question !!!!! ?

[ranworthbreeze]

Hi MM,

I think you will find that Meg is female.

Regards

Alan

[Guest ExMemberKingFisher]

You need to remember that there are two things at play here. First the incoming tide which will ebb and flow approx. twice per day. It's more like a 25hr cycle during which you get two high and two low tides. The second is the rivers are actually trying to drain the land up river and will always try to flow down river. On a canal you normally moor facing up river because the water only ever runs one way, unlike on the rivers where it is tide influenced.

So the river is draining and the tide starts to come in, at which point it forms a rising watery dam that initially slows the outgoing river and eventually rises enough to reverse the direction of the current. This gives rise to a strange phenomenon most likely to be witnessed at Yarmouth, Berney Arms or Reedham where you will notice the tide is still flowing out, yet the boat and water level is starting to rise. This is where the incoming tide is running in, with the outgoing river running out over the top and gradually running out of steam before being forced back. It is the point at which the incoming tide has matched and stopped the outgoing river that slack water occurs which is about 1.5hrs after low water at the yacht station. For anyone who is critical on clearance at the bridges they probably need to leave on low, as opposed to slack water, which gives the greater clearance.

Further up river the incoming tide will have the effect of causing the water to rise  due to the river not being able to drain due to the incoming tide. At places such as Norwich or Coltishall, especially after a heavy rain you will still see the water running down river due to the excess water draining from the land, whilst the water will still be rising due to it being held back further down river. In these places all that happens is that the current weakens towards high water and strengthens again towards low water.

Once the tide turns the dam is effectively removed and the river can start draining faster again. Because it takes time for this draining effect to be felt up river the low water time at Wroxham is approx 4.5 hrs after low water at Gorleston. Likewise the effect of the incoming tide is also felt about 4.5 hrs after high water.

The above is also affected by the height of the low or high tide, the direction of the wind, the amount of recent rainfall and restrictions such as bridges.

[SwanR]

Kingfishers Time that makes sense to me. Thank you for your explanation. 

[Meg]

Thank you everyone especially Kingfishers Time, I grasped that finally. Water is obviously tricky stuff and not to be taken lightly!

[MauriceMynah]

I'm sorry for my earlier confusion Meg. For absolutely no good reason I took "Meg" to be your boat name and for no explicable reason for you to be male. For that I apologise unreservedly.

My query about tides is the time spent coming in and going out. I sort of think that the tide at Potter Heigham  spends more time going out, than it does coming in, where at Gorleston it spends about 6 and a half hours going out or coming in.  Could that be correct?

[Guest ExMemberKingFisher]

24 minutes ago, MauriceMynah said:

I'm sorry for my earlier confusion Meg. For absolutely no good reason I took "Meg" to be your boat name and for no explicable reason for you to be male. For that I apologise unreservedly.

My query about tides is the time spent coming in and going out. I sort of think that the tide at Potter Heigham  spends more time going out, than it does coming in, where at Gorleston it spends about 6 and a half hours going out or coming in.  Could that be correct?

MM, With regard to your observations about Potter and the amount of time spent for it going out, vs it coming in, are you basing that on the visible flow of current you can see, or the rise and fall? I suspect that due to the land mass above the bridge being drained by the Thurne and the restriction of the bridge you will often see current flowing downriver, whilst the water level is actually rising and clearance diminishing under the bridge.

If I was to slowly raise a physical barrier at the mouth of the Thurne, say 2inches per hour, you would see water flowing downriver through Potter bridge to fill the void behind the barrier, but at the same time as it fills and rises you would see clearance under the bridge diminish, yet to all intents and purposes the tide is going out, but all the barrier is actually doing is mimicking a rising or high tide.

I suspect that with the land mass to be drained above Potter bridge, even if it didn't rain for several months, there would still be enough water draining out of the water table to give a visible flow out under Potter bridge in all but the highest of tides.

[MauriceMynah]

Ahh ha, here we have my first problem. It was not an observation but a thought, perhaps even a query. I do not know and I have not observed. I'm not nit-picking there, and my interest is in the rise and fall alone. the direction of the current only becomes relevant to me on the other thousand or so questions I have. (which also I'm unable to work out how to phrase)

[Polly]

At the flood the tide fairly hosses upstream, I have paddled a boat up there on the 3RR , it was going past the boat like a flipping train about four inches from where I was kneeling!

[Bound2Please]

If there was no wind, rain, land drainage, no air pressure changes, the moon would control the rise and fall of the tides rise and fall. Add earths natural weather elements in and it all becomes rather unpredictable, as so much to do with the weather can affect the tides timings rise and fall etc. All the theories are just that, all tide tables have printed on them tidal predictions for xyz, at southend say today they could be correct, but at yarmouth they could be abc minutes out either way.

Charlie

PS ....River flows are not the same as predicted tide times, they can affect them either way.

[MauriceMynah]

What I need to have done is a time lapse camera on the PHB pilots bridge height gauge taking a pic every 15 mins,  for 13 hours, on a day when it's an average tide no wind and average air pressure, then do the same for neaps and again for springs. That would answer one of my questions.

[marshman]

So - you have all forgotten the twelves rule and the fact that in Broadland rivers the ebb seems to run for 7 hours whilst the flood is nearer 5 hours.

Add that to the equation and no one has any answers - add the further  impact of high and low pressure, and its a surprise that they bother to even publish tide tables!!!!

[Malanka]

I agree with Marshman

The thing to remember is that water is an incompressible liquid, which means that it can't be compressed in any way, all it can do is get thinner (shallow) and thicker (deeper) when in a channel, air pressure over the top resists this increase and helps the  decrease in depth and therefore the ends move futher away as pressure in the middle can't compress it (decrease volume) so it gets longer effectively (think of a hydraulic mechanism like the canal lifts).

 

There is also the phenomenon of river running out and tide coming in at the same time so the water is flowng down river but at GY for instance the bridge heights get lower at the same time. A greek chappy worked all this out in a eureka moment thousands of years ago, I still struggle with it. My answer is to use my mark 1 eyeball and take into consideration what the tables tell me, but upstream rainfall, changes in land use (crops vs no crops) and air pressure potentially  make huge differences to water levels on the Broads. We see these differences as "Oh that's not what the table says...."

 

As in all things from official bodies its bucket of salt and engage common sense time.

 

M

[TheQ]

1 salt water is heavier that fresh water, therefore when the tide starts flowing in the water beneath is flowing in while the water on top will flow out (at first)

2, The water doesn't take 4.5 hour to reach Potter from Yarmouth , it pushes the water In front of it while raising the level. Except when you go from  a high air pressure period lowering the north Sea, to a low air pressure  raising the North sea. Then enough Salt water flows up  the system to produce the fish kills we get around Potter.

3 I've been at Horning (Technically Hoveton) above Black Horse broad, in a rescue boat being pushed by the tide upriver at 1 MPH against the wind.

4,  At Potter Bridge, the tide is sufficiently strong coming in to Make it very difficult to paddle against it.

5, The tidal cycles on  the broads are very approximate, I always allow for an extra Hour tide going out than coming in, which allows the rain  water to escape.

6, Then you have the air pressure to contend with, and that is compounded with the wind blowing down the north sea. if the get Low Air pressure, with the wind blowing down the north sea and heavy rain. then Norfolk is in trouble as it's the recipe for floods..

 

A bit of an officious way of putting it but it's the only way my brain keeps a clue as what going on...

 

[marshman]

All a bit Norfolk to me - stick your finger in the air and hope you get a signal!!