Taller waves on low tide?

Discussion in 'Weather and Surf Forecasting' started by civilengsp, Jun 24, 2014.

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  1. civilengsp

    civilengsp Member

    7
    Jun 24, 2014
    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. live4truth

    live4truth Well-Known Member

    866
    Feb 9, 2007
    Click here... Doesn't help directly, but should send you in the right direction...
     

  3. seldom seen

    seldom seen Well-Known Member

    Aug 21, 2012
    My spot loves an outgoing. High tide can swamp it out if there's not enough swell.
     
  4. dave

    dave Well-Known Member

    427
    Dec 11, 2008
    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. civilengsp

    civilengsp Member

    7
    Jun 24, 2014
    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!
     
  6. seldom seen

    seldom seen Well-Known Member

    Aug 21, 2012
    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. peakhunter

    peakhunter Well-Known Member

    81
    Sep 5, 2013
    depends on the bathymetry, generally yes
     
  8. capecodcdog

    capecodcdog Well-Known Member

    Jun 22, 2012
    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.

    Read more: http://www.waterencyclopedia.com/Tw-Z/Waves.html#ixzz35aGEysDM

    Of course there is this oceanography gem someone posted elsewhere:

    http://oceanworld.tamu.edu/resources/ocng_textbook/chapter16/chapter16_01.htm
     
    Last edited: Jun 24, 2014
  9. sisurfdogg

    sisurfdogg Well-Known Member

    Jun 17, 2013
    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. zach619

    zach619 Well-Known Member

    Jan 21, 2009
    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.
     
  11. zach619

    zach619 Well-Known Member

    Jan 21, 2009
    To your first point, The mid-atlantic states and the states to the North do not suffer from such enormous tide swings as we do down here, and the areas to our north are FAR less tide dependent. So what you witness is obviously true, but imagine what you notice, being magnified. Welcome to South Carolina. I was actually talking to a life guard the first week I moved here. He had his uniform on but had a surf board, so I asked him about a certain spot and it's restrictions, and he chatted with me for about 5 minutes. He gave me the most true statement that anyone has every given me down here: He said, EVERY TIME THERE IS SWELL, you MUST hit it 2.5-2 hours BEFORE high tide. The tidal push and surge is the ONLY time that you will get the maximum output of force and wave form. He said, about 30 minutes prio to a true high tide, the waters start moving around and you will experience an immediate lull and it will get worse and worse as the tide falls out. He said in order for anything to break here, anywhere near low tide, you need the monster of all swells...

    Long story short. You CANNOT surf in this state at low tide because of this, unless its a cat 4. And this has held true for 2 years now. about 2 hours before the high tide, the sets start getting big and clean, and then for about 45 minutes to an hour, the sets get more and more constant. What I take from this, is that especially for wind swell, which is mostly what we get, you will always see hundreds of waves go by that were "ALMOST" breaking. They want to. You see them coming, you get ready, but at the last minute, you see that they are just a little too close together and it just didn't happen. When the tide gets dialed in, and it is maximizing everything, I think most of those little ripples that would have almost broken, well they start to break. Its a short 1-1.5 hour window, where all the variables are in the positive and more waves start to break, then boom. its gone. So, its the same energy in the water, but for that tidal surge, right at the end, all of the waves that never would have broken a couple hours before heave everything they need to provide a good wave.

    Anyway, I notice that too for sure, and unfortunately, I have to schedule all of my sessions around this as a result. I miss the days of never even looking at what the tide was doing, and those days where it only goes 3-4 feet in either direction... I mean, we have the largest tide swings until you get up into NS I think. Its incredible, and it is the reason that we have the seafood we have, why the oysters are the best in the world and everything else, but it KILLS the surf. Its like a damn surf assassin. Mix that with the Gaskin Banks and damn b, you gotta be a wave hunter.
     
  12. seldom seen

    seldom seen Well-Known Member

    Aug 21, 2012
    Damn man, makes me feel fortunate to be where I am. That adds a whole extra level of planning to take into consideration. Farking amazing though when ya think about it, how the same energy can manifest itself in so many ways. Definitely observed that 'almost breaking' effect you refer to, (not a total sesh killer tho) and oddly enough, it happens at high tide at the spot I'm thinking.

    Sisurfdog- thanks man at least I know I'm not losing it:cool:

    Dudes, another crazy thing about tides. In my lobstering days we pulled 10 pot trawls, figure each pot weighs 50 lbs on average, with enough buoy line that at slack tide the it would feel weightless. When You grab the buoy line to put in the hauler, you can literally feel what the tide was doing...you'd go from grabbing what felt like just a piece of rope at slack tide, next trawl after the tide change you'd literally have to fight the line to walk it up to the hauler, it'd feel like hundreds of lbs. The power of water man...
     
  13. zach619

    zach619 Well-Known Member

    Jan 21, 2009
    Yeah man, it's weird down here. Unlike anywhere I have ever lived, or even gone. Ocean City was way less tide depended and would start working for me just a couple hours after low tide usually. The thing that we DON'T have here, that ales the mid atlantic is the shore break... It was crazy the first time I came home from the west coast to Ocean City. It had been about 4 years or so since I had been, and I was surfing around mid town, and I was hitting floaters and jumping off onto sand so I didn't break my fins. I actually damaged 2 boards in one day. It was chest to head high, off a little stub jetty, but it was amazing to see how far out the wave start to break, then it mutates and gives you only one option if you want to complete the wave, and that is do get one more move in and then land in sand. It was just funneling into the beach...

    Its just crazy how everywhere is so different. You can surf around here when the tides arent perfect and stuff, but there is just such a world of difference when things are all dialed in.

    Its just crazy to me that we don't get all the shore break that jersey and delmarva do. I guess our shelf is even more gradually sloped. Maybe when the do the next beach replenishment in a couple years, it will be gnarly shore break everywhere. Been about 7 years now, and I have never been here on or around a beach replen, so we will see.. Maybe that is why....
     
  14. seldom seen

    seldom seen Well-Known Member

    Aug 21, 2012
    Well at least you got the skim if that happens:cool:
     
  15. capecodcdog

    capecodcdog Well-Known Member

    Jun 22, 2012
    With regard to wave height, I concur that the bathymetry the critical factor. At some spots, what I have observed, if you examine a particular spot at high tide, that wave may barely show a "bump". However, as the tide lowers, the swell will "jack up" and create a breaking wave.

    Of course, with larger swell/more wave energy, the same spot may break at higher tides. At the beach I frequent, there are spots that higher tides kill, and others that still work somewhat at higher tides. Contrarily, when larger swell events occurs, there are spots that jack up and dump into shallow water at low tide (that work well w/ smaller swells), and I generally avoid, as this is a bone/board breaking scenario.

    So it helps to know your beach/break, and how swell levels/periods, tides, and of course winds work. Observing and making mental notes, and even keeping a notebook, of these things helps "figure it out." I know Zack is "in deep" with this stuff, taking it further and writing software for his area that uses these factors. All helps with planning, etc., but bottom line is you have to go check it out.
     
  16. civilengsp

    civilengsp Member

    7
    Jun 24, 2014
    First of all, thanks for your reply. I'm actually studying the case from an engineering point of view. I've done the statistics from data obtained from offshore virtual buoys and calculated a series of wave heights and periods for a certain return period. I'm simulating those results on a model, so I'm reproducing those events in the exact same conditions for both highest high tide and lowest low tide. In terms of bathymetry, the slope is really mild... I'm not seeing any irregularities along the vicinity of the breakwater. Even though, after running multiple simulations, I'm obtaining these weird results of taller waves at low tide. I've done other studies in other locations and yes, I've always had taller waves at high tide...

    Any ideas about this? :confused:

    Once again, I really appreciate all of your contributions!
     
  17. Sandblasters

    Sandblasters Well-Known Member

    May 4, 2013
    thewave.jpg

    not always zach, this was like 2 or 3 years ago 1 hour after low on a 8 foot swell rolling in,which switched to 35mph offshores at mid tide which was night by then but was semi closed out and very shallow busted a fin box pulling into one, i wish i had pics of that day but the gorpo died and i had to take it off because it was to (heavy) but one day we will charge gaskin on the next hurricane swell, there are tiger sharks the size of cars out there but as i said before if your willing to paddle out im going with you just let me know, because alone that is just to damn risky. i love risk but you dont want to paddle out into a one of the biggest shark breading grounds on the coast alone.
     
  18. Sandblasters

    Sandblasters Well-Known Member

    May 4, 2013
    but for the most part your spot on, this day was a rare instance hadnt seen one like it in a long while.
     
  19. Mitchell

    Mitchell Well-Known Member

    Jan 5, 2009
    Which model are you using? SWAN? Maybe at a low enough tide the water depths further offshore are shallow enough to cause some wave refraction focusing energy at a particular location, while at higher tides the deeper water doesn't allow this.
     
  20. zach619

    zach619 Well-Known Member

    Jan 21, 2009
    Nice man. Thats what thew guy told me though, if its a macking swell, there will be barrels all over the place. But in my almost two years of living here, the MAX swell that has hit was Sandy. I am sure you surfed it. It was no where near 8 feet. It was fun as hell, 5-6 maybe, but just didnt have enough juice to hollow out at the low tide. It just died. Maybe as the swell built, before the sun came up, at its max, sandy was delivering, but high tide was mid morning that day. It was fun. But I am frothing for a swell like the one in that pic. As the new guy, you gotta hit a brother up when that happens and show me the ropes. ya heard?