Quote Originally Posted by civilengsp View Post
Thank you all for your answers.

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.