Re: Discrepancy between COTW Coyote tides and Ken's SM tides

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Date: Thu Aug 24 1995 - 23:47:14 PDT 

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Date: Fri, 25 Aug 1995 02:47:14 -0400
From: Gr8Jibe@aol.com-DeleteThis
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Subject: Re: Discrepancy between COTW Coyote tides and Ken's SM tides

In a message dated 95-08-24 16:40:21 EDT,Jim Paugh writes:

> The
>differences in height are off by less than a foot, is that beyond
>acceptable tolerances? ;^)

Depends on what fin you're using I guess. I asked Jim Martin to put the tide
heights on the beeper specifically so we'd know the depth of sandbars at low
tide at 3rd Avenue.

>What I would like to hear is an explanation of why slack current occurs
after
say, a low tide. For instance, today, low tide at Crissy is at 5:03pm, but
low slack is at 7:29pm! How is it that slack current occurs 2.5 hours after
low tide?

I think of this question in two ways--the wave theory and the bathtub theory.
First the wave: Tides are waves of very long wavelength that pass through the
bay. Low tide is the trough, high tide is the crest. But the water movement
associated with the wave does not stop precisely as the wave crests or
troughs, as the wave is continuing on its way.

Now the bathtub: The Sacramento and San Joaquin Rivers are like a faucet
filling a bathtub at a steady rate. The Golden Gate drains the tub during
ebb tide. As soon as the rate of water draining out the GG falls below the
rate the rivers are filling the bay, the water level will begin to rise, even
though the ebb has just slowed.

We're just rubber duckies on the big bathtub.

Bill

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