Re: [Paddlewise] Tides and Current Speed

Craig Jungers wrote:

> Well I'll go along with that. But I can think of a couple of ways to
> actually measure current speed to see how fast the current actually ramps
> up. I'm pretty sure that in constricted channels it gets to very nearly full
> speed quickly... nothing like the nice smooth curves you see in tidal tables
> or on the Internet web pages.
> 
> I would have thought some geophysical science post-grad would be all gung ho
> about doing this sort of thing.

I believe NOAA set up current meters in selected channels and actually did 
the measurements for a few, generated the algorithm which seemed to fit 
best, and then extrapolated that to other areas where no actual 
measurements were taken and called it good. Given other variables which 
changed from day to day would throw the models off anyway, it probably was 
not going to improve things much if they set up current meters in every 
tidal channel.

To be sure, the smooth curves are idealized results.  But, the shape of the 
curves is not the same for all channels; some are asymmetric; others are 
symmetric.  My experience on the Columbia using a modeling program (Tides 
and Currents from Nobeltec) suggests they are within a half a knot most of 
the time, except when in the input of fresh water from tributaries or 
through Bonneville Dam is very high or very low.  In the big flood of 1996, 
they were off by 3 knots, everywhere!  [More on that flood: 
http://www.cpc.noaa.gov/products/assessments/assess_96/pacnw.html ]

Researchers, one a guy I have known for 30 years, are still gathering 
detailed current information on the lower Columbia River system and 
attempting to model the flow in more detail, under US Navy funding, I 
believe.  I see their ships and their continuous long term CTD buoy arrays 
in the River regularly.  For complex systems there is more effort required 
than a grad student in a cubbyhole somewhere can provide.  More field data 
is needed.

I can understand about half of what my buddy tells me about this stuff when 
he comes to visit, and will send you his email so you can put your 
challenge to him personally if you want.

-- 
Dave Kruger
Astoria, OR
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