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Old 03-28-2015, 06:12 PM   #21
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No...well beyond my capability. I've just had conversations with Rick Thomson about it several years ago now. His big emphasis at the time was the proud effect of the Fraser on local current dynamics. It flows at >10,000 cubic meters/second on some years at full freshet.

Rick also explained why my prawn pots moved in the opposite direction to wind during a particularly strong wind in Howe Sound one winter past.


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Old 03-28-2015, 07:56 PM   #22
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Amazingly enough, the Fraser freshet runs all the ways up to Powell River. I've flown over the Strait of Georgia every week for years and I still look down out the window and watch the water.

The rapids in this area should be respected.

In river talk they turn class 4 to 5 depending on the exchange.
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Old 03-28-2015, 08:42 PM   #23
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We've never had trouble with finding slack. What we have had trouble with is the yahoos who roar through at 15 knots leaving giant wakes and standing waves. Given that there is always a bunch going thru at slack, rig for serious rolling before you enter because "they" will be there.
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Old 03-29-2015, 08:53 PM   #24
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Hmmm! Rick Thomson's book is available to download as a PDF. It's a big download so ensure you are on Wifi....

http://www.dfo-mpo.gc.ca/Library/487.pdf



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Old 03-29-2015, 09:27 PM   #25
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"RESIDUAL PLUS TIDAL STREAMS The tidal stream contribution will now be discussed in relation to the estuarine current. In the absence of any surface wind drift, the sum of these two accounts for nearly all the observed current speed and variability. Tidal streams are that part of the total current directly associated with the rise and fall of the tide; except where deflected by the bottom topography or coastline they produce no significant net drift over a period of a few tidal cycles, just as the tide produces no net change in the water depth. In reality, of course, those who make tidal predictions lump the pure tidal streams together with the residual currents to get a sort of hybrid tidal flow, a procedure that can be erroneous unless the residual current remains almost constant over many weeks and months. As the residual flow is not generally constant because of variability in the various mechanisms that produce it, current predictions are often incorrect, particularly for times of slack water." Page 209 from Thomson, R.E. 1981. Oceanography of the British Columbia Coast. Can. Spec. Pub. Fish. Aquat. Sci. 309 p.

The above pertains to the effect of estuarine flows from rivers, which are not constant throughout the year. This probably means that estimates of currents "particularly for times of slack water" from tide tables will be in error during freshets (May, June) and during periods of low flows (December, January).


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Old 03-30-2015, 07:37 PM   #26
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Jim,

The questions I would have:

Aren't typical seasonal variations in river flows already taken into account in the published tables, since they are based on measurements?

How large are the effects of year-to-year variation in river flows on tides and currents at a place like Yuculta?
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Old 03-30-2015, 08:30 PM   #27
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My take is that river flows are at best an average based on flow meter measurements.....not any more accurate than an Verage
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Old 03-30-2015, 08:30 PM   #28
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Estimating Tidal Currents for Dent Rapids, Gillard Passage and the Yucultas.

Quote:
Originally Posted by QB View Post
Jim,

The questions I would have:

Aren't typical seasonal variations in river flows already taken into account in the published tables, since they are based on measurements?

How large are the effects of year-to-year variation in river flows on tides and currents at a place like Yuculta?

I get the sense that they probably are not taken into account. If they incorporate seasonal variation, the interannual effects would not be included of course and would result in prediction error. I will try and ask one of the IOS types if I get the chance.

Your second question is a very good one and I cannot answer it. I would suspect that the freshet coming out of Bute Inlet may have a pretty pronounced effect on the currents in this area.

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