Tidal range not understood.

[toyboy]

I sail on the Orwell and next year I may venture further away but I am stumped by tidal calculations probably because I haven't understood the cause correctly.
On the Orwell we have a tidal range between tides of between 3-4 metres. I understood tidal ranges should be equal all around the British Isles. I always thought water levels should be the same everywhere as water flows into the lowest point thereby making all water levels the same at the same states of tide.

Can anybody explain why different parts of the country have different tidal ranges?

 

[Koeketiene]

Google & Wikipedia are your friend.
They explain it better than I ever could.

The typical tidal range in the open ocean is about 0.6 metres. Closer to the coast, this range is much greater. Coastal tidal ranges vary globally and can differ anywhere from near zero to over 11 metres.
The exact range depends on the volume of water adjacent to the coast, and the geography of the basin the water sits in. Larger bodies of water have higher ranges, and the geography can act as a funnel amplifying or dispersing the tide.
The world's largest tidal range of 11.7 metres occurs at Burntcoat Head in the Bay of Fundy, Eastern Canada.
The Bristol Channel, between England and Wales in the United Kingdom, regularly experiences tidal ranges of up to 9 metres.
Some of the smallest tidal ranges occur in the Mediterranean, Baltic, and Caribbean Seas. A point within a tidal system where the tidal range is almost zero is called an amphidromic point.

 

[ex-Gladys]

Some of the simple things to consider is that tides are driven by a number of factors such as the position of the mon, the distance between earth and moon, the position of the sun relative to the moon, and the distance from the sun to name but 4. These are all when you graph them out against time sine wave type shapes, and when you combine sine waves you can make pretty much any type of wave shape you like (including a square wave). This leads to some places in the world having (very counter intuitively) only one tide per day - Mexico and Vietnam... There are also "resonances" that occur, so along the south coast there are places where the tidal range is very small (Poole) compared to a few miles away

 

[toyboy]

Google & Wikipedia are your friend.
They explain it better than I ever could.

I know some rivers in different countries to ours get bigger tides. What I cannot understand is why UK rivers do not rise and fall the same amount as water stays pretty level I always thought. I can understand the River Seven having large tides as the tide become funneled into a smaller space but even then I am not sure how water behaves that way?

 

[toyboy]

Some of the simple things to consider is that tides are driven by a number of factors such as the position of the mon, the distance between earth and moon, the position of the sun relative to the moon, and the distance from the sun to name but 4. These are all when you graph them out against time sine wave type shapes, and when you combine sine waves you can make pretty much any type of wave shape you like (including a square wave). This leads to some places in the world having (very counter intuitively) only one tide per day - Mexico and Vietnam... There are also "resonances" that occur, so along the south coast there are places where the tidal range is very small (Poole) compared to a few miles away

Yes I understand tides but I do not understand why places on the same coast have differing heights of tide?

 

[Pye_End]

It is a dynamic situation and always changing, so water cannot find it's own level in these circumstances. Think of a rock in a river - the water height before it is considerably higher than after it. Now scale that up to a coastline and you can imagine some very significant differences even a short distance away.

 

[AliM]

The tidal heights around a coast are dominated by the flow of water around that coast. After all, if it was just the influence of the moon and sun, then all one side of the earth would have the same time of high tide - so where would all that extra water come from? Around the British isles, the tides come around the North of Scotland and around Cornwall and into the channel. It all gets horribly complicated as these flows interfere with each other. Actually, it can be modelled from fluid dynamics, given a decent computer, but the details of the whole picture are beyond an intuitive understanding!

 

[guernseyman]

Here in the Bay of St Malo, sailing is all uphill or downhill with spring tide heights varying from 6 m. in Alderney, 10m. in Guernsey, to 13 m. in St Malo.

 

[Bob Stays]

There is a reasonable explanation of tides in general on the BBC Coast TV program
http://www.bbc.co.uk/programmes/b01jxxll
But to answer your question, I think you have to look at tides on a macro scale so water moves up the West coast of the UK and up the English Channel. And just like water flowing up a river in that it will not make high water at all the points along the river at the same time. So water flowing up the English Channel will create a high tide at Plymouth 19:33 today before high tide at Swanage 22:32. (hmmm harder to explain that I thought) Reeds Almanac also has a good chapter about how the Flood works around the UK in Chapter 4 section 4.7.3 (2012 version)
Interestingly enough the actual mid-day high tide today at Harwich is significantly less than predicted - So what happened to the storm surge?

 

[Pye_End]

- So what happened to the storm surge?

it is forecast for tonight not for now. The lowering of the tide was also predicted, eg. http://www.ntslf.org/numerical-modelling/latest-surge-forecast?port=Sheerness

 

[Bob Stays]

Ahh thanks for that - absolutely correct - will watch tonights hightide with interest. Also I have reread the thread and realised I was not answering the original question which was about the difference in Range of tides not the difference in time of the high tides. my apologies.

 

[toyboy]

It is a dynamic situation and always changing, so water cannot find it's own level in these circumstances. Think of a rock in a river - the water height before it is considerably higher than after it. Now scale that up to a coastline and you can imagine some very significant differences even a short distance away.

I believe I am starting to realise what maybe the bleeding obvious

 

[toyboy]

The tidal heights around a coast are dominated by the flow of water around that coast. After all, if it was just the influence of the moon and sun, then all one side of the earth would have the same time of high tide - so where would all that extra water come from? Around the British isles, the tides come around the North of Scotland and around Cornwall and into the channel. It all gets horribly complicated as these flows interfere with each other. Actually, it can be modelled from fluid dynamics, given a decent computer, but the details of the whole picture are beyond an intuitive understanding!

Yes it was the normal tidal stuff I was mixing up with funneling and stuff causing different levels on the same tide.

 

[toyboy]

There is a reasonable explanation of tides in general on the BBC Coast TV program
http://www.bbc.co.uk/programmes/b01jxxll
But to answer your question, I think you have to look at tides on a macro scale so water moves up the West coast of the UK and up the English Channel. And just like water flowing up a river in that it will not make high water at all the points along the river at the same time. So water flowing up the English Channel will create a high tide at Plymouth 19:33 today before high tide at Swanage 22:32. (hmmm harder to explain that I thought) Reeds Almanac also has a good chapter about how the Flood works around the UK in Chapter 4 section 4.7.3 (2012 version)

Interestingly enough the actual mid-day high tide today at Harwich is significantly less than predicted - So what happened to the storm surge?

I watched that prog. The trouble is the scenery is always so brilliant I never remember the info bits. I even have a Reeds Almanac but since the farce of the day skipper course I haven't looked at it nor any of the other piles of RYA books I bought. There was a prog on the other night called Orbit I believe which I have had to save to my video recorder for when I have the time to study it.

 

[toyboy]

Ahh thanks for that - absolutely correct - will watch tonights hightide with interest. Also I have reread the thread and realised I was not answering the original question which was about the difference in Range of tides not the difference in time of the high tides. my apologies.

Everything on here is interesting thanks.