Current chart for rivers?
The OP was asking about paddling up tidal rivers.
Are there current charts for tidal rivers? Upstream?
The current in a tidal river is going to be a composite function of the natural fresh water flow, which will always be downstream, plus the salt water inflows and outflows caused by the varying tides. I don’t see how there can be any chart that could predict this composite accurately unless the river was completely empty of natural flow, in which case the Rule of Twelfths will accurately apply.
I suppose there could be a chart or table that calculated current in a tidal river based on different assumed CFS volumes of fresh water flow. Are there such things? I’d be interested in knowing.
Of course, in the open ocean, where the only thing affecting water level is the tides, the current directions and speed can be accurately calculated from the tidal elevations alone (not counting wind effects, which can also change current speeds and water depths).
Yes there are
Here is a link to the NOAA Tidal Currents Predictions for Connecticut. There are half a dozen stations on the Connecticut River. If there is an unusually high flow coming down the river that will effect the timing and speed of the predicted current somewhat, but just as with Tides, predictions are just predictions. Factors in the real world will make the actual Tides or Currents differ slightly from the tables, but the tables are your best starting point for having any idea of what to expect.
Nate
Thanks again
Thanks so much everyone. I love the paddling.net message boards. We did get out a paddle around a bit on the Farm River yesterday – a few hours after low tide on a very calm day with almost no wind. It was great. Very placid with almost no significant current in either direction. The rocky coastline was beautiful and the river itself seemed quite clean (though muddy).
I loved the discussion of tides vs currents and have learned a lot. Thanks for sharing your wisdom!
Jill
Great!
There was a lot of information posted that might not apply now but as you travel farther into bigger waters is handy.
When I find a bunch of info I make a Word document and copy and paste…
Its way easier to find on my hard drive than coming back here and searching.
more on tides and currents
BTW, I looked up the 50/90 rule and thought others might find this link interesting, which explains the differences between the Rule of Thirds, Rule of Twelfths and the 50/90 Rule:
http://paddlenhull.blogspot.com/2009/10/rules-for-tides-thirds-5090-twelfths.html
Might work for New England
with semidiurnal tides but it is not always applicable.
Our tides here are regular.
Do NOT count on regular tides when you go to the Gulf of Mexico…putting any faith in the rules presented will leave you in hot water…
The time lapse between highs and lows is not regular…It can be three or seven hours…and sometimes a high is a low high…or the low a low high…
Down there winds have a tremendous influence.
Know if you are dealing with a diurnal semidirunal or mixed tide.
http://oceanservice.noaa.gov/education/kits/tides/tides07_cycles.html
Nate, thanks but no link
You make an important point in explaining that tide level is not the same as current speed and that the Rule of Twelfths technically concerns level.
However, I was concerned with giving generic advice about paddling a generic tidal river. In a real inland river, we are talking about a single channel formation. All the fresh water will only flow downstream. Every molecule of saltwater on the incoming tide will try to go upstream, and every molecule will come back downstream on the outgoing tide. Hence, tidal levels will always translate into upstream currents or downstream currents. There is no other direction for the water to go. Hence the tidal component of the current speed should be related closely to the Rule of Twelfths and the other two rules.
Of course, absent a table as for the Connecticut River, there is no way to calculate actual current speed unless you know the size and shape of the river channel and the gradient. Even then, the entire current speed exercise goes beyond the simple thing I was trying to communicate to novices in Northern California in 2005.
I'm assuming paddlers who have no shuttle and want to begin and end their trip at the same place on the tidal river.
My advice for this kind of trip on a tidal river, wherever you put on it, is to go upstream first. If you have a simple understanding of the 6 hour tide rate cycle, put on the river about halfway through the incoming tide for a six hour day trip. You don't need to know the actual current speed. What you do know is that this is your best tide cycle chance of paddling upstream. If it's too hard to go upstream at this point in the tide cycle, it will only get worse later. So, don't paddle downstream in this river because you won't be able to get back up later in the tide cycle.
Go to a lake instead. Or the movies. Or pnet.
Thanks for the Info
Thank you Glenn and others. I recently paddled in the Bass River in Cape Cod and wondered about how to better prepare for the water conditions related to tidal and other effects.