Biology Reference
In-Depth Information
boat. The pump included a long tube that could be lowered to various
depths in the water column to gather plankton samples. On that trip, he
remembers a freshwater pulse coming down the river, resulting in dra-
matic two-layer flows. On the surface, the water was flowing at the fast clip
of more than two feet per second; on the bottom, it was also speeding by at
two feet per second—but in the opposite direction.
The sampling started out smoothly enough. As the scientists dropped
the pump in the upper part of the water column, it moved along with the
vessel and surface currents. But the minute the pump dropped into the
lower part of the water column, disaster struck. “The pump went one way
and the boat went another, and the tube suddenly took off, straight into
our props,” says Burau. “The props usually chew things up, but this was a
big tube, 4-5 inches in diameter. Things did not look good.”
The captain threw the anchor in response. Just about then, Burau
looked up and noticed a huge ship coming around the bend. “It seemed
like a 15-story building was headed straight for us,” he recalls. he two
captains had a rapid radio exchange, with one warning of restricted ma-
neuverability, and the other responding, “looks like you're right in the cen-
ter of the shipping channel.” The ship started turning, but continued bear-
ing down on them sideways with the tide. Burau's crew retrieved their life
vests and got ready to jump, but at the last minute the ship just missed
them. “That's the kind of trouble you can get in because the estuary can
flow in different directions at the same time,” he says.
Anyone who has ever stood on the Golden Gate Bridge in a T-shirt and
wished for a down jacket knows that the wind blows hardest through the
narrowest parts of the estuary. Strong winds also brew in spring and sum-
mer due to temperature differences between the warm valley inland and
the cool ocean offshore. Northerly winds drive surface waters out of the
estuary, and southerly winds drive water into it.
Wherever the wind blows, it pushes the water into waves. A moderate
summer wind can generate a wave half a meter high and two seconds long;
a wave whipped up by a winter storm can last as many as five seconds.
These waves reverberate down to water depths of about 10 feet but often
don't affect deeper parts of the bay.
The readings from the 1850s Coast Geodetic Survey for San Pablo Bay
suggest that it was not always so uniformly shallow and wide. The survey
found two big, deep channels: one leading up into the Petaluma River and
one into the Carquinez Strait. Myriad smaller channels extended the paths
