Thread: How do tides work?

I understand why we have high tide etc ...

but how does the tide level work ... for example why does novascotia have higher tides than new jersey ...

or why does one coast of Panama have higher tides than the other coast when it is only seperated by a few miles at its closest point?

Originally Posted by tom

I understand why we have high tide etc ...

but how does the tide level work ... for example why does novascotia have higher tides than new jersey ...

or why does one coast of Panama have higher tides than the other coast when it is only seperated by a few miles at its closest point?

It's not Nova Scotia, per se, it's the eastern most part of the Bay of Fundy, where tidal waters are funneled into a much higher tide. Pugwash, Nova Scotia, is only a couple dozen miles from Truro, where the Salmon River experiences a massive tidal bore from the Bay of Fundy. As you can see from the tide tables for Pugwash, at that link, the tides are fairly mild.

The same sort of variables cause tide differences all over the world.

Originally Posted by tom

I understand why we have high tide etc ...

but how does the tide level work ... for example why does novascotia have higher tides than new jersey ...

or why does one coast of Panama have higher tides than the other coast when it is only seperated by a few miles at its closest point?

There is a very good article about tides in wikipedia: Tide - Wikipedia, the free encyclopedia

The height of tides in various places is really a function of resonance. In all places there are 12h25m and 24h50m components to the natural tidal forces (and some other modulations). So does the ocean, sea, bay etc naturally resonate at or near those periods? If it is finely tuned to that period then a small force may cause a much larger outcome. If not, it may be smaller than otherwise expected.

The difference on two sides of Panama is clearly very different oceans.

I live in New Zealand, and I was surprised to learn that the South Island of NZ always has the tide in somewhere and always out somewhere. Work that one out!

I have been told that 'US' astronomers have know idea about tides.. and this young person began to wave his arms about talking of the moon and the sun and how its all 'hours' late because of global weather changes... Ummm...No. I said. Land mass shapes and coastal shapes tend to funnel the movements of tides and disturb what forces the Moon and Sun exhort upon Earth's Oceans... Yes its a science field, all of its own. No mystery here.

There's a place called Pugwash???
Now I'm off to work with "The Black Pig" playing in my head.

I once watched the tide change, in the Orkneys. Between two islands, between the Atlantic and the North Sea, the sea-level was 3ft higher on one side than on the other (in a line from one island to the other) and the water was running like a river over a weir.

Originally Posted by TaoZero5

There's a place called Pugwash???
Now I'm off to work with "The Black Pig" playing in my head.

I once watched the tide change, in the Orkneys. Between two islands, between the Atlantic and the North Sea, the sea-level was 3ft higher on one side than on the other (in a line from one island to the other) and the water was running like a river over a weir.

I live in Auckland. We have two harbours and the tides are 3 hours different in them. You can stand in some places and see both. If a channel was cut it would flow substantially, one way or the other, most of the time.

Originally Posted by RayTomes

I live in Auckland. We have two harbours and the tides are 3 hours different in them. You can stand in some places and see both. If a channel was cut it would flow substantially, one way or the other, most of the time.

Sounds like a possible way to minimize the tidal effects in the harbors while generating a substantial amount of electricity.

The Southern harbor is Manukau, but the Northern harbor, over which the Hwy 1 bridge passes, doesn't appear to be named on Google maps. Does it have a name? I see Shoal Bay and Ngataringa Bay, but I don't see a name for the entire harbor.

Originally Posted by mugaliens

Sounds like a possible way to minimize the tidal effects in the harbors while generating a substantial amount of electricity.

The Southern harbor is Manukau, but the Northern harbor, over which the Hwy 1 bridge passes, doesn't appear to be named on Google maps. Does it have a name? I see Shoal Bay and Ngataringa Bay, but I don't see a name for the entire harbor.

It is called "Waitemata" harbour.

Any power generation would need to work from only modest height differences, but could certainly have a huge flow, as the tasman sea and Pacific Oceans are both huge. Interestingly a tidal power project has just been started in the kaipara harbour slightly further north. Will be interesting to see how it goes.

Oops... we are getting off topic, but as a fellow NZ'r I think a channel for shipping and power generation could be a great idea..

It could generate enough power to sell to the 'Grid' and pay for itself...

I have often thought that the Panama Canal could be a power station...

Originally Posted by astromark

Oops... we are getting off topic, but as a fellow NZ'r I think a channel for shipping and power generation could be a great idea..

It could generate enough power to sell to the 'Grid' and pay for itself...

I have often thought that the Panama Canal could be a power station...

As I was writing out the idea of harnessing the tidal differences between the two bays, I was thinking the same thing about the Panama Canal. The highest point in the Panama Canal, however, is 85 feet above MSL, and to take advantage of any tidal differences between the Gulf of Mexico and the Pacific Ocean, they'd have to dig down at least 115 feet for nearly 8 miles, not to mention lesser depths but for many more miles. Of course doing so would negate much of the reason behind the locks of the Panama Canal in the first place: It was cheaper to construct locks than it was to dig. They could have dug until they had sufficient draft below mean sea level (perhaps 100'). If they'd done that, they'd only need one lock.