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Subject: TWL: San Francisco versus Columbia River
From: Michael Maurice (mikem@XXX.XXX)
Date: Sun Dec 01 2002 - 11:00:24 EST
I have been doing a comparison of these 2 entrances and just for the
practice I thought I would write up some of it. Since these are the only 2
entrances which are what I would call Class One, on the Pacific US Coast,
they make for an interesting compare.
Here-in-after referred to as SF for San Francisco and CR for Columbia River.
CR is one of the 3 dog leg entrances on the coast; in that you approach
from the SW and before you get across the bar you have to make a 45 degree
turn to the right, going in; Grays Harbor and Humboldt Bay being the others.
SF is a straight shot from the sea buoy until completely inside the
entrance, east of the bridge. Although you can approach it in small ships
and under from the sides through the Bonita Channel or South Channel.
Both entrances are dredged to about the same depth 48-55 feet, SF being 55,
but CR has up to 80 feet scoured out right at the turn on the north center
of the channel. SF has about 200 feet deep from about Pt. Bonita Light
east, just past the bridge. The SF main channel is narrower than at
Columbia River, being 2000 feet wide versus CR which is 2550 feet wide.
However, CR is wider in practical terms since the entrance is not as
shallow outside the dredged channel as at SF.
CR has no protection from surrounding land mass, SF has a fair amount from
the NW.
The nearby land mass at CR is mostly sand beach whereas SF is mostly rock
and cliffs, which reflect waves back into the ocean, making for a very
confused sea on occasion.
Aids to navigation at SF in the main channel are fewer and end at #8, where
as CR has buoy numbers up to 14 before getting to the safe area inside the bar.
Ship traffic is different. More and bigger ships at SF, moving at higher
speeds.
More tugs with long tows at CR and more big fishing boats.
Tides average about 8-10 feet at CR and about 3-6 feet at SF.
Current speeds are lower at SF, but on average not a lot.
The tidal prism at SF is much larger owing to the trapped bay water inside,
but CR has large freshwater runoff sometimes. The distance across both
entrances is about the same but SF is 200 feet deep in the constricted part
where CR is about 65 feet on average. At SF when just past the 200 feet
deep area, the entire area, to the west/south/north is very shallow, mostly
about 25-30 feet and extends for about 5 miles.
At CR the shallow area past the jetty tips only for about 2 miles and then
drops off nicely past 100 feet.
CR has a sophisticated range light system, with a main range light visible
for 5 miles or more and Sand Island range which carries you across the bar.
SF has no range lights, but has several white marker lights along the coast
at the beginning of the constricted area.
Capt. Mike Maurice
Wilsonville, Near Portland Oregon
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