A little about tides - Part2

In my last post on tides, I explained what I had recently learned about how they work. It is not necessary it read first, but in case you want to, here is a link to it. In this post, we will look at the Bay of Fundy, which if you don’t know has the highest tides in the world, up to 50’. Going to visit there is on my bucket list. It was on my mother’s bucket list too, but she never made it, giving me a little extra motivation to do it for her, too.

A couple of years ago, I saw an explanation for why the tides are so high there that finally was clear to me. What puzzled me was that the video I referenced in the previous post gave a different reason for why the Fundy tides are so high. Both explanations depend on the geography of the area but in different ways. Let’s look at both explanations.

The first explanation is because the bay is roughly funnel shaped. Image a wave of water entering the bay. As it moves up, the volume of the water is not changing, and because it is so immense, it is not dissipating. So as the cross section of the bay decreases, the “cross section” of the wave needs to increase. The only way for the cross section to increase is in height. Tidal maps indicate that the farther up the bay you go, the greater the tidal effect. That makes sense.

The second explanation is that the resonant frequency of the Bay of Fundy is very close to the tidal frequency. Huh? In other words, the tides are creating a standing wave in the Bay of Fundy. Come again? Take 3. Did you ever take a bath and move your body back and forth at just the right speed so that you created a huge wave that splashed outside the tub and made a huge mess? Congratulations, you made a standing wave. Supposedly, that is what is happening in the Bay of Fundy. It is just the right size and shape such that its natural frequency is about 2 cycles/per day. So now we know what Paul Bunyan used to do when taking baths in the Bay of Fundy.

So which one is right? As I read the Wikipedia article about it, it seems to be both. “Because of tidal resonance in the funnel-shaped bay, the tides that flow through the channel are very powerful” Emphasis added. Tidal resonance is the second explanation and funnel-shaped is the first. My short take is that tidal resonance causes the wave entering, and exiting, the bay to larger than typical and the funnel shape amplifies the effect. Which contributes more? I will let someone else crunch those numbers to decide. If you are working on your graduate degree in oceanography, maybe that can be your thesis or dissertation. Please give me a hat tip if you do.