I've been wondering about water dynamics in narrow ocean channels. Are you more likely to encounter strong turbulence on extreme high tides or on lower tides? On Nov. 3rd I helped organize a practice rescue session in Baynes channel just off of Victoria BC. This day was recommended to me because it was suppose to have been day with a strong ebb current off a high tide. While the current was strong it was not particularity turbulent. Without years of ocean experience to back me up I am, nevertheless, beginning to think that you're likely to find more turbulence when there is less water flowing over or through restricted passage. I suppose my conclusion depends on whether the rough water is created by the topography of the bottom or by water trying to flow past a choke point such as opposed head lands. On this particular day we had the strong current but little turbulence. The only rough spot was right at the head land. After a week of steady southeast winds blowing against the current, on the 3rd, the wind disappeared along with the rough water. We had been looking forward to really gnarly conditions. I concluded that next time I'd do the exercise on a day of strong currents but not an extreme high tide. Any comments? Are my conclusions correct? *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Warner Family <hmgwarner_at_shaw.ca> wrote: >> I've been wondering about water dynamics in narrow ocean channels. Are you more likely to encounter strong turbulence on extreme high tides or on lower tides? [snip] Without years of ocean experience to back me up I am, nevertheless, beginning to think that you're likely to find more turbulence when there is less water flowing over or through restricted passage.>> I think you've got a good point: that an extreme current will produce more turbulence when the water level is low, assuming it is obstructions under the surface that help generate the turbulence, as well as flow past points. However, to get an extreme current, the water level __normally__ has to be somewhere near mid-tide, because the __normal__ high current time is about halfway between high tide and low tide. So, it's not likely you will find a place that has extreme current at low water. It might be useful to set up the lawn chair on a high point and watch one of your favorite turbulent spots throughout the middle of the ebb (or, flood), and see what happens. -- Dave Kruger Astoria, OR *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
----- Original Message ----- From: "Dave Kruger" <kdruger_at_pacifier.com> > It might be useful to set up the lawn chair on a high point and watch one of > your favorite turbulent spots throughout the middle of the ebb (or, flood), > and see what happens. I am not certain that would work, although it would be fun especially with a bottle of tequila and sangrita chasers to cozy up with. The reason I say that it likely would not work is that there are so many more variables involved in the water dynamics than just the straightforward movement of water through the areas in questions in relationship to the tides. Even that "straightforward" movement is tricky enough because of the bottom surface of the passages involved. To all of this you have to add the effects of wind, barometric pressure, any fresh water flow, phases of the moon, relative location of the moon in its orbit (perigee vs. apogee). I remember years ago, one local chap here who would go down to the waters off the Battery (southern tip of Manhattan and therefore at the apex of three pathways of water: the Hudson, the ocean and the East River, itself a tidal estuary) and try to study patterns of movement compared to what the tide and currents prediction tables said. It was basically a fool's errand. I have never seen the waters here do the same thing twice in relationship to the prediction tables. You sometimes think you have the patterns down to at least a sense of tendencies, then the next time you are completely fooled when the waters decide to do something else. ralph diaz *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Depth, features, etc all play into this and there is no answer that applies across the board. In most cases the current speed is one of the larger factors so the comment about that (I forget who made it) is probably right on target. More food for thought: I am not sure how constricted of an area you are talking about, so the following may or may not be relevent. In whitewater paddling we look at flow and gradient. Basically the more flow the less gradient you can handle and vice versa. In extremely low volume conditions (< 100cfs) a skilled creeker might be able to paddle a 600 ft per mile or greater gradient. In a high volume situation it would be possible for a 30 ft per mile run to be unrunnable. Of course all this is an over simplification, since there are many other factors. Another thing that happens is that a rapid may wash out at a given level and then reappear with a vengance at a still higher level. There are places where there is a waterfall flowing one way at one tide state, a waterfall flowing the other way at another, and flat water at yet another. I have never witnessed this first hand but have seen som impressive pictures of such a "reversing falls". Sorry if all of this just muddies the water, but the point is that there is no one correct answer except, "it depends". Pete __________________________________________________ Do you Yahoo!? Yahoo! Mail Plus - Powerful. Affordable. Sign up now. http://mailplus.yahoo.com *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Ralph's point is well-taken, hence the emphasis on __normal__ in my original post. (I especially like his addition of the sangria!) Complicating matters in his Hudson River/East River/ocean example is the interplay of those three influences. Even here, at the mouth of the Columbia (one river/ocean interaction), sometimes the estuary will do one thing , sometimes another. I'll stand by my original assertion that under normal circumstances, the max flood (or ebb) is at mid-tide. Estuaries complicate things, but that general principle stands. And, observing one's favorite spot over a tidal cycle will normally show local anomalies not noted on the tide/current charts. -- Dave Kruger (hardly ever normal) Astoria, OR -- "Dave Kruger" wrote: > > It might be useful to set up the lawn chair on a high point and watch one of > > your favorite turbulent spots throughout the middle of the ebb (or, flood), > > and see what happens. "ralph diaz" wrote: > > I am not certain that would work, although it would be fun especially with a > bottle of tequila and sangrita chasers to cozy up with. [snip] > I remember years ago, one local chap here who would go down to the waters > off the Battery (southern tip of Manhattan and therefore at the apex of > three pathways of water: the Hudson, the ocean and the East River, itself a > tidal estuary) and try to study patterns of movement compared to what the > tide and currents prediction tables said. It was basically a fool's errand. > I have never seen the waters here do the same thing twice in relationship to > the prediction tables. You sometimes think you have the patterns down to at > least a sense of tendencies, then the next time you are completely fooled > when the waters decide to do something else. *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
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