Riding the current - was Riding down the Hudson River
This brings up a topic that has puzzled me for years. I have a hard time getting my head around the relationship between tide and current. In my feeble brian, the current should be in sync with the tide...that is to say that at high tide, the current should stop and reverse. At low tide the current should stop flowing and then reverse. Why in the hell does slack high (or low) water not coincide with high or low tide. What is the relationship between the two? The more I study the tables, the more confused I become!
Regards,
Randy Pickelmann
hard aground in Clearwater, FL
Morning Star
lying Solomon's, MD
www.CruisingMorningStar.com
An example, maybe?. Let's say you are mid-point in the area of tidal flow. The area "up" stream will continue to accept water- tidal flow, but in the area where you are at, the flow isn't enough to make the level rise any more- stand. Essentially, the water that is coming in is being displaced at the same rate by that which is flowing out... and vice versa. (or is it vise versa?) You still have flow, but no rise or fall. (I'm thinking that makes sense.)
Rudy
Briney Bug, Panama City, Fl
On Tue, Sep 20, 2011 at 9:54 AM, Rudy and Jill rudysechez@yahoo.com wrote:
An example, maybe?. You still have flow, but no rise or fall. (I'm thinking that makes sense.)
Tide range and current flow is highly dependent on topography of
bottom, Two extreme examples would be Bay of Fundy facing the
atlantic North of Maine and the Mediterranean facing the opposite
side of the Atlantic just south of Spain with virtually no tide to
speak of.
One body of water is a wide funnel opening that compresses the
incoming bulge of water because it keeps narrowing down until there is
a 50 foot high bulge at high tide.
The PNW has some of the fastest tide races you can imagine. due to the
convoluted geography found there..
You guys have it far too easy in east coast florida waters.
Snip:"...The PNW has some of the fastest tide races you can imagine. due to
the convoluted geography found there..You guys have it far too easy in
east coast florida waters...."
Arild,
The Georgia bite experiences that same funnel effect, however certainly not
to the degree of the examples you gave. Tidal ranges of 6-11' catch novice
transients off guard and the 3-4 knot ebb current in some spots (Altamaha
River on ebb, Ashley River and Elliot's cut in Charleston) as well. As far
as flow and rise ...there are some pills that can help with that :).
Joe
About to sneak into Harrisvile Harbor MI, Lake Huron to hide for a day from
winds demons...
M/V "Carolyn Ann" GH N-37
MTOA# 3813
AGLCA# 5485 (Gold Looper)
CarolynAnn-N37.blogspot.com
Sorry if I inadvertently stepped on anyones toes. Rusy ws looking for
examples to illustrate the point why maximum current dod not
coincide with maximum or minimum tide I simply offered some
examples from my own background.
From having taught the Power Squadron classes for about 20 years I
was at one time familiar with the wat it worked. I always visualized
the process like water sloshing from one basis to another , velocity
was a function of relative elevation between two points . As the lower
basis filled it acted as a damper on inflow thus slowing down the rate
of flow.
I can't say the availability of electronic tide tables has improved
matters. We can find the exact time and speed for any given station
but ther still seem to be a gap when it comes to estimating values in
between reference stations.
Arild
On Tue, Sep 20, 2011 at 11:08 AM, Joseph Pica joseph.pica@gmail.com wrote:
Snip:"...The PNW has some of the fastest tide races you can imagine. due to
the convoluted geography found there..You guys have it far too easy in
east coast florida waters...."
Arild,
The Georgia bite experiences that same funnel effect, however certainly not
to the degree of the examples you gave. Tidal ranges of 6-11' catch novice
transients off guard and the 3-4 knot ebb current in some spots (Altamaha
River on ebb, Ashley River and Elliot's cut in Charleston) as well. As far
as flow and rise ...there are some pills that can help with that :).
Joe
About to sneak into Harrisvile Harbor MI, Lake Huron to hide for a day from
winds demons...
M/V “Carolyn Ann” GH N-37
MTOA# 3813
AGLCA# 5485 (Gold Looper)
CarolynAnn-N37.blogspot.com
The relationship between tide and current is complex. Two simple cases
-
"standing wave" - a round deep bay with a narrow mouth. The tide comes up and the flood at the entrance starts (slack before flood) when the water level outside is higher than inside. The water level outside reaches it's highest level and begins to go down (slack before ebb). Then the ebb current empties the bay.
-
"progressive wave" - a long narrow channel like the hudson river has a progressive wave. High tide and max flood are at the same time and same for low tide and max ebb. The tide and current have the same " phase". Think of the oscillating current in a common wave at the beach. The crest pushes you toward shore and the ebb is the undertow.
All current-tide height phases are somewhere between standing and progressive.
All of these phenomena are waves and must be analyzed as such. Bay of Fundy and Easter Long Island Sound tide amplification phenomena are harmonics generated because the length of the basins are 1/4 of the driving wavelength of the dominant M2 or lunar tide. Think of a jump rope held at two ends. You can flick the rope at just the right frequency to make the rope jump out of the other persons hand. Same phenomenon.
Lots of other strange interactions take place between the various tidal components and the land.
Ever wonder why it's always low tide in the early morning on Fl sw coast? And it's close to low tide simultaneously all around the Gulf of Mexico?
Now you all can find errors in my descriptions based on your own observations because as I said, it's complicated.
Gregory Han
PS I used to do this stuff for a living a long time ago
On Sep 20, 2011, at 8:52 AM, Randy Pickelmann rwp_48@yahoo.com wrote:
This brings up a topic that has puzzled me for years. I have a hard time getting my head around the relationship between tide and current. In my feeble brian, the current should be in sync with the tide...that is to say that at high tide, the current should stop and reverse. At low tide the current should stop flowing and then reverse. Why in the hell does slack high (or low) water not coincide with high or low tide. What is the relationship between the two? The more I study the tables, the more confused I become!
Regards,
Randy Pickelmann
hard aground in Clearwater, FL
Morning Star
lying Solomon's, MD
www.CruisingMorningStar.com
On Tue, Sep 20, 2011 at 12:40 PM, Lists hangreg@gmail.com wrote:
The relationship between tide and current is complex. Ever wonder why it's
always low tide in the early morning on Fl sw coast? And it's close to low
tide simultaneously all around the Gulf of Mexico?
REPLY
That's because everybody knows you can only make great coffe at low time.
High tide would dilute the water in pot and affect the flavor.
The Med does not have a significant tide because the lengths of the basins do not resonate with the frequencies that force lunar and solar tides. The adriatic sea in fact does have the proper shape and does have some tidal height variation. It is not entirely because of the narrow entrance at Gibraltar as you might think.
I find that seamen are experts in observing what they can see from their deck but very lacking in the information necessary to discover WHY things happen as they do. That takes observations over various scales of time and space and the application of fundamental physical principles. For example Matthew Fontaine Maury quantified the Western Boundary Current known as the Gulf Stream by painstakingly plotting hundreds of current calculations from ships logs.
Gregory Han
Via iPad
On Sep 20, 2011, at 1:54 PM, Arild Jensen arild.jensen195@gmail.com wrote:
On Tue, Sep 20, 2011 at 9:54 AM, Rudy and Jill rudysechez@yahoo.com wrote:
An example, maybe?. You still have flow, but no rise or fall. (I'm thinking that makes sense.)
Tide range and current flow is highly dependent on topography of
bottom, Two extreme examples would be Bay of Fundy facing the
atlantic North of Maine and the Mediterranean facing the opposite
side of the Atlantic just south of Spain with virtually no tide to
speak of.
To All,
I was up in the Saguenay River to do a current study with the tides. Low and
behold when the tide rises the current at the surface was is in the opposite
direction and when the tide was on its way out the surface current was in
the opposite direction. My findings were that the river is 350' deep and
when the tide would rise (flood) the water came from the bottom pushing
upwards and when it reached the surface water was abundant and had to flow
somewhere and that was downstream or opposite of the flood and the same when
the tide was going out the surface current was in the opposite direction.
Then I started talking to the locals and they were amazed to learn this.
Then I made an exercise with the locals. I simulated a boat sinking... gave
them lat and long of the incident and let them look for debris. Life
jackets, oars, ring buoy, cooler, poly line, 3 cushions were items they had
to look for. I had a boat follow the items for the fun of it. The locals
were looking upstream for the items and one hour later they gave up and we
called the follower of the items and he was six miles downstream. In that
area there was 20 feet of tide. I forever study water in tidal areas...
Regards,
Roger Lalonde
Summerstown On Canada
-----Original Message-----
From: Randy Pickelmann
Sent: Tuesday, September 20, 2011 8:52 AM
To: trawlers@lists.trawlering.com
Subject: T&T: Riding the current - was Riding down the Hudson River
This brings up a topic that has puzzled me for years. I have a hard time
getting my head around the relationship between tide and current. In my
feeble brian, the current should be in sync with the tide...that is to say
that at high tide, the current should stop and reverse. At low tide the
current should stop flowing and then reverse. Why in the hell does slack
high (or low) water not coincide with high or low tide. What is the
relationship between the two? The more I study the tables, the more confu
sed I become!
Regards,
Randy Pickelmann
hard aground in Clearwater, FL
Morning Star
lying Solomon's, MD
www.CruisingMorningStar.com
http://lists.trawlering.com/mailman/listinfo/trawlers_lists.trawlering.com
To unsubscribe or modify your subscription options (get password, change
email address, etc) go to:
http://lists.trawlering.com/mailman/listinfo/trawlers_lists.trawlering.com
Trawlers & Trawlering and T&T are trademarks of Water World
Productions. Unauthorized use is prohibited.
NOAA has provided a succinct description of tides and currents relationships with diagrams and examples. http://tidesandcurrents.noaa.gov/faq4.html
Gregory Han
Via iPad
On Sep 20, 2011, at 8:52 AM, Randy Pickelmann rwp_48@yahoo.com wrote:
This brings up a topic that has puzzled me for years. I have a hard time getting my head around the relationship between tide and current. In my feeble brian, the current should be in sync with the tide...that is to say that at high tide, the current should stop and reverse. At low tide the current should stop flowing and then reverse. Why in the hell does slack high (or low) water not coincide with high or low tide. What is the relationship between the two? The more I study the tables, the more confused I become!
Regards,
Randy Pickelmann
hard aground in Clearwater, FL
Morning Star