Thread: Taller waves on low tide?

1. Junior Member
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Jun 2014
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Taller waves on low tide?

Hi there everybody.

I'm new to this forum and I've been searching for an answer to this question like mad, but nobody knows what to say about it. I analyse marine climate through numerical modelling, but I've found something that isn't very logical to me: I'm having taller waves on low tide than on high tide. I know you surfers understand the mechanics behind waves, so, what do you think? Is this possible to you?

Thank you very much in advance!

2. Click here... Doesn't help directly, but should send you in the right direction...

3. My spot loves an outgoing. High tide can swamp it out if there's not enough swell.

4. Senior Member
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MB 07750
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the waves' energy pushes the water upwards, when its shallow at low tide, the wave has less space between its bottom and the ocean floor so the energy pushes the water higher or taller as you put it. When its deeper such as during high tide, the wave energy has more room to push down

5. Junior Member
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Jun 2014
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I'm trying to define the worst situation for a breakwater. The wave height is the reference parameter to do the calculations. So, what I understand in my case study is that, at low tide I'm having a taller wave but also a lower water column, whereas at high tide, even though I'm registering smaller waves, I also count on the tide... In conclusion, at high tide the water height is always bigger (the difference in wave heights from low tides to high = 1.64 ft; tide = 9.2 ft).

Thanks again!

6. Since we're talking tides....

here's a couple observations I think I've noticed. Been meaning to start a thread on this but I'll post 'em here if that's ok with the OP. And I know waves, tides, and the ocean and everything involved are very dynamic and complex...these are just speculative things I've picked up on.

1/Set interval- this really only applies to short period windswell, but I feel like the final hour before peak high tide is often when that 'never ending set' happens. You know, when you're waiting for a lull to paddle out and you think the last wave of the set is breaking than boom, here comes the next. I feel like the tidal surge can push sets a little closer together.

2/Rips- this is like clockwork at my go to, but it's waaay rip-ier on the mid-incoming to high tide. More frequent ones and stronger. Like to the point that pre-set where you're sitting is good, then a big(relative terms) set pushes through the exact spot but now it's the middle of a rip. Not saying there won't be rips at lower tides, but I feel like when the full force of the ocean is pushing towards the shore, and all that water from the last set that broke has to get back out, this is what happens.

7. Member
Join Date
Sep 2013
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81
depends on the bathymetry, generally yes

8. Some info for the noodle (maybe TMI):
http://www.dfo-mpo.gc.ca/Library/487-12.pdf

Widgets/Calculators/Charts & Graphs:

http://www.meted.ucar.edu/marine/widgets/

From http://www.waterencyclopedia.com/Tw-Z/Waves.html:
Breaking Waves

As waves approach landmasses, the wave base begins to contact the sea floor and the wave's profile begins to change. This friction slows the circular orbital motion of the wave's base, but the top continues at its original speed. In effect, the wave begins leaning forward on its approach to shore. When the wave's steepness ratio reaches 1:7, the wave's structure collapses on top of itself, forming a breaker.

A spilling breaker is the classic rolling wave coming up a gradually sloping sandy beach. The long incline drains the energy of the wave over a large area.

A plunging breaker approaches a steeper beachfront and forms a curling crest that moves over a pocket of air. The curling water is traveling faster.

The classic curl of a breaking wave is associated worldwide with surfing. As a wave approaches shore, friction slows the bottom of the wave while allowing the top to continue moving, which causes the top to lean forward in this manner.

The classic curl of a breaking wave is associated worldwide with surfing. As a wave approaches shore, friction slows the bottom of the wave while allowing the top to continue moving, which causes the top to lean forward in this manner.

than the slowing wave base, and the water outruns itself with nothing beneath for support.

Of course there is this oceanography gem someone posted elsewhere:

http://oceanworld.tamu.edu/resources...apter16_01.htm
Last edited by capecodcdog; Jun 24, 2014 at 06:52 PM. Reason: added ocng_textbook .. SI greymatter and what not

9. Senior Member
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Originally Posted by seldom seen
here's a couple observations I think I've noticed. Been meaning to start a thread on this but I'll post 'em here if that's ok with the OP. And I know waves, tides, and the ocean and everything involved are very dynamic and complex...these are just speculative things I've picked up on.

1/Set interval- this really only applies to short period windswell, but I feel like the final hour before peak high tide is often when that 'never ending set' happens. You know, when you're waiting for a lull to paddle out and you think the last wave of the set is breaking than boom, here comes the next. I feel like the tidal surge can push sets a little closer together.

2/Rips- this is like clockwork at my go to, but it's waaay rip-ier on the mid-incoming to high tide. More frequent ones and stronger. Like to the point that pre-set where you're sitting is good, then a big(relative terms) set pushes through the exact spot but now it's the middle of a rip. Not saying there won't be rips at lower tides, but I feel like when the full force of the ocean is pushing towards the shore, and all that water from the last set that broke has to get back out, this is what happens.
Your rip current observations are right on bro! The higher tide and the extra energy will punch a gap in the sandbar, creating a channel for the rip to form. All the extra water bearing in on shore has to go back out (unless the dune is breached in big time storms), so it goes out the gap in the sandbar. The volume of water out the gap far exceeds the amount going in the gap, since most incoming water is still going over the bar all along the beach. I always tell inexperienced swimmers to watch out on the incoming tide. It is counter intuitive to them - they think incoming tide will push them in, outgoing tide will suck them out, but it doesn't work that way.

10. Originally Posted by civilengsp

I'm trying to define the worst situation for a breakwater. The wave height is the reference parameter to do the calculations. So, what I understand in my case study is that, at low tide I'm having a taller wave but also a lower water column, whereas at high tide, even though I'm registering smaller waves, I also count on the tide... In conclusion, at high tide the water height is always bigger (the difference in wave heights from low tides to high = 1.64 ft; tide = 9.2 ft).

Thanks again!
I guess it depends on what you consider "wave height" and it also depends on your location. NOAA and all the buoy data that I filter and run algorythms on, measure \$WVHT or "waveheight" as the mean size of the wave from the sea level, above. And by sea level, that is the ocean surface, regardless of tide. So, none of the swell models that I know of, take tide into consideration, especially since most data is pulled from offshore buoys.

So, bathometry is your main factor hear, where in some locations, with reefs and underwater obsitcles, as the tide gets lower, it forces water upward. This is why on a swell of 10ft @ 18 seconds will make a reef break, generally, almost 30% taller than a beach break right next to it, and that is just the force of an underwater object making the water move somewhere, which is up, which increases the side.

Generally speaking, on a sandy beach, "Most" anywhere, if you are talking literally low tide, I.E. the lower the ocean level gets in a cycle, then the wave size will always be smaller. And by that, I mean, if the tide rises from low to high, and the exact same swell is in the water, and doesn't change the whole time, the waves will always be bigger, the more tide you have. The dynamics will be different, mushy etc... but mathematically speaking, the rise of the tide will increase "waveheight" in almost every application, as long as the force behind the swell stays constant.

Wave rich places, like CA will break on high and low tides, but the waves will get super racey and much smaller as the tide gets to it's literal low point.

In a nut shell, in my opinion, with your original statement, I would say the opposite it true.

If you are looking at this from a non-surfing standpoint, and strickly a scientific one, you need to understand how the data that you are probably seeing gets gathered, and more importantly, how it is applied. Because again, in my opinion, the amount of water below a waves face and the ocean's surface is irrelevant in relation to "wave size"... Meaning, a 6 foot wave is a six foot wave when it has 2 feet of tide under it, and a six foot wave is a six foot wave with 6 feet of tide. It does not mean that a 6 foot wave is 8 feet because it has an extra two feet of water under it, and it does not make a 6 foot wave a 12 foot wave because it has 6 feet of tide....

Just my thoughts. It really depends what you are using this for. Because if you are applying it to the structural integrity of a breakwall etc, sure the tides are to be considered, and maybe you are looking for the overall "SEA HEIGHT" and not truly looking at "wave height"... The total sea height, and tide lines are different than what a wave height is....

So dealing with breakwall, you are probably trying to figure out the maximum height that water levels will get to, given certain swell sizes and tide... I.E. will a 10 foot wall at beach XX be tall enough to hold the maximum swell at the highest tide.