Saturday's Bridge Walk yesterday was delightful. Patrice Williams (sans son Miles who was visiting Grandma), Richard Koss, Bradford Hodach, Leland Lee, Rick Sheridan, his friend Monya and her friend Shelley, gathered on a sparkling morning next to San Francisco Bay where Marina Green meets GGNRA.
This time we were armed with Sibley's Field Guide to Western Birds, as recommended by Leonard Blumin, our bird guide, along with wife Patti, on a previous jaunt. Now when we see a bird, we have a chance of finding out something about it, provided we can link it to a photo before it flies off.
Things got off to a bad start when Rick spilled that I'd had yet another birthday the day before and the students, reeling from Wednesday's exam where I'd hit them with four essay questions instead of the usual three, evened the score by singing Happy Birthday, thank you.
"Our consolation," Richard said, "was to figure that you had to read all the extra Blue Books." Yes, but one question was take home and all the writing still had to be crammed into three hours, thus the net effect was the same (you can only write so much in three hours), and this forced you to hit the high points instead of descending into minutiae, was my reaction.
I'd have to read more good stuff, less B.S., I hoped.
We'll see when the Blue Books arrive next week.
Normally it takes an hour and a few minutes for the round trip, walking briskly for exercise, with no stops for birds or flowers. This time we spent two, and then went to the Grove on Chestnut Street, nearby, for a bite and some more chatting. With exams over, the time pressure was off. This trip we looked for Anna's Hummingbird at the spot we know he likes to perch, and saw him again. If Anna is looking for him, we know where she can find him.
We also saw the orange-footed Snowy Egret once again, peering and spearing.
And the black cormorant diving and popping up just his neck and head.
These are all hard-working birds.
Here are a few more photos (click to enlarge) of some of the things we see on a Bridge Walk:
What? You say that doesn't look like the Golden Gate Bridge? Those are the bridge tower footings on a (different) day when the fog has come in on more than little cat feet.
This is the tidal gauge house on the old Coast Guard pier. According to a recent article in the S.F. Chronicle, it is home to one of the oldest tidal gauges in the world, operating since 1851. In 1855, according to the account, the operator noticed that the paper readout showed pen-lines indicating an unusual wave pattern that he couldn't account for, so he sent it back to headquarters in Washington, D.C. for his supervisors to interpret. By the time it arrived (Pony Express?), word had been received of a tsunami in Japan weeks before. From that scientists were able to calculate the average depth of the Pacific to within plus or minus ten percent. Why anyone would want to know the average depth of the Pacific is a different question. Across the Bay, in the background, you can see the buildings of Fort Baker, in Marin, new home of the U.S. Coast Guard for San Francisco. See below for the article in the S.F. Chronicle describing the tsunami that revealed the depth of the ocean.
This is the old boat house adjacent to the Coast Guard pier. There was a rail track allowing life-boats to launch beyond the surf line for rescue missions when every minute counted. Now it houses a sea-life museum, as the Coast Guard has moved to Fort Baker on the other side of the bridge in Marin.
This hip-roofed home was the residence of the Coast Guard commandant, adjacent to the boat. When a ship went aground on the rocks of the Golden Gate, you wanted the boss on hand to direct the crew to the rescue without delay, so he lived right here next to the beach and boat house.
Fishermen and crabbers on the mine pier adjacent to the Warming Hut where souvenirs and snacks are sold to visitors. During the war, this pier served to supply vessels with floating mines to protect the harbor from invasion. The mines were assembled in shacks now converted to comfort stations.
This commercial fisherman is returning early in the morning after what may have been days at sea.
The fog has lifted, ...but not much.
As you approach Fort Point, under the Bridge, you see the rock-ribbed coast of San Francisco. Only seagulls, sea-lions, and surfers swim here, and not many of those.
As we approach the Bridge, we see both towers, the fog having lifted more as the morning draws on. The new police speedboat enhances harbor security after 9-11.
This crane soars, yet it is not a bird. The Bridge is undergoing a retrofit to protect against the Next Big One, as San Francisco is earthquake country.
This iron chain keeps the sea away from the people, or the people out of the sea. I'm not sure why it's there, but it's been there for a long time, as the rusted links in the next photo reveal.
Each link is the size of grapefruit, and probably a lot heavier.
Surfers steer clear of these.
The promenade we enjoy was made possible through the generosity of these folks, according to the plaque.
Folks love to stroll the beach. They'll often toss a ball into the bay for their dog to fetch.
Alcatraz in the background.
Carl Sandburg's poem about the fog with the little cat feet.
Let's not forget to take a moment to look at the flowers along the way.
Lavender colored daisies. I'm about as knowledgeable about plant names as bird's. I hope that doesn't mean I have to buy a book on flowers. We'll be carrying too many books on the Bridge Walks, which are supposed to be a respite from the books.
PWF. Pretty white flower.
How succulent, red.
Sic transit...
The whole idea of the Crissy Marsh was to restore the shore to the way it was before the white man arrived and messed things up. The Golden Gate National Recreation Area occupies, in this area, the former Presidio of San Francisco, the garrison-fort established by the Spanish in 1776 to protect their silver mines near Santa Fe, New Mexico, which seems a long distance away, but if you have silver mines, I guess that's what you do. You secure potential invasion routes.
After the United States took over the Presidio, it became home to the Sixth Army. The Presidio based the forces which occupied the Philippines in 1898 under Gen. Arthur MacArthur, father to Douglas "I shall return" MacArthur of WWII fame, the American Caesar, according to biographer William Manchester, after Admiral "You may fire when ready, Gridley" Dewey (see the monument to him in Union Square, downtown San Francisco) sank the aging Spanish fleet in Manila Bay, marking U.S. entry onto the world stage as an imperial nation, projecting power abroad through military force.
Do you know why they call it Union Square, incidentally? Because it marks California siding with the Union during the Civil War. California Gold financed the North in that struggle over the nation's soul. You can find a lot of links to Constitutional Law on a Bridge Walk, if you let yourself.
The Army filled in the marsh along the Bay at the Presidio, building a grassy airstrip in the '20s, and concrete parking lots thereafter. When the GGNRA took over as the Presidio was phased out, the concrete was torn up, a pond was dug, and the sandy dirt moved along to what is now a new grassy field. The Promenade, referred to above, is what we walk along on our bridge walks, unless we decide to hike along the hard sand along the water's edge at low tide, as we did yesterday.
In the picture above, you can see a line of rocks. Human engineers installed those during the construction of the marsh, two straight lines of rock to provide a channel for tidal waters to charge and discharge the pond twice daily. The channel is about twenty feet deep. I watched it being dug by bulldozers, on my frequent walks. Today it is filled in almost completely.
Mother Nature had a different idea than human engineers, and now the marsh pond is blocked. Once previously, the bulldozers came back to open a new channel straight to the Bay, but once again, Mother Nature had a different idea. The channel filled with sand, the course made a 90-degree curving turn to the right exiting into the Bay, and as the result of recent high water, is now fully enclosed, awaiting the next storm season, I guess. The birds don't seem to mind. Nature seems to ignore human engineers who insist on straight lines when we all should know by now that soft curves are a lot more beautiful and effective at making the world go around.
See you next Bridge Walk.
The San Francisco Chronicle
SECTION: BAY AREA; Pg. B1
LENGTH: 1372 words
HEADLINE: SAN FRANCISCO;
TIDES OF HISTORY;
Presidio gauge has measured the bay's rise and fall for 150 years
SOURCE: Chronicle Staff Writer
BYLINE: Carl Nolte
BODY:
A
tiny, wooden white building with a red roof at the end of a pier near
Crissy Field in the Presidio of San Francisco is so obscure it doesn't
even have a sign -- but this is one of the country's major scientific
landmarks, the oldest continually operating tidal gauge in the Western
Hemisphere.
The 150th anniversary of tidal observations will be celebrated this week on the date the first bit of data was recorded, June 30, 1854. Only one other tide house -- in Brest, France -- has continuous records that are as old. All the others -- and there are 174 in the United States alone -- have had the reports interrupted by storms, disaster and human carelessness.
"It is a very unique hydrographic record," said Steve Gill, a scientist with the National Oceanic and Atmospheric Administration.
Though measuring the rise and fall of the tides appears to be among the simplest of natural observations, data gathered from the tides at the Golden Gate has helped scientists unlock such mysteries as the depth of the Pacific Ocean, climate change and understanding earthquakes. And establishment of mean sea level is the way all elevations are measured.
"This particular gauge has a record of adding to our knowledge of the oceans and its relationship with the Earth that is without peer," said Albert Theberge, the director of NOAA's central library.
"In its way, it was a pioneer of the global system," said Ben Sherman, an NOAA spokesman.
Tides and currents have always fascinated humans who lived along the seashore. From the ancients who puzzled over the rise and fall of the waters, to Shakespeare ("There is a tide in the affairs of men ...") to Longfellow ("The tide rises, the tide falls...") to Churchill, who called the swing of fortunes in World War II "the turn of the tide," the tides have been both a physical presence and a metaphor.
Tides, of course, are important in the affairs of ships, helping to move everything from foreign cars to container ships full of running shoes arriving by sea. Some vessels that draw a lot of water can only come in and out of San Francisco Bay at times of high tides. Many tanker ships can only move up the bay to ports in Solano County, Contra Costa and upriver on the flood tide.
The tides are caused by the Earth and moon revolving around a common center of gravity, and the Earth in turn revolving around the sun. NOAA's Theberge calls the tides "a grand symphony that has been played out for billions of years -- an orchestration of moon, sun, Earth and ocean."
"The motions are manifested by predictable but changing gravitational forces acting on the atmosphere, the oceans and the solid Earth itself," Theberge writes.
The causes of tidal action were not understood until 1687, after famous discoveries by Sir Isaac Newton. The next step was learning how to predict the tides, and in particular how to factor in various different conditions, including the shape of various shore and sea basins. This depended on the advance of technology.
In the United States, President Thomas Jefferson established the Coast Survey in 1807 -- the country's oldest physical science agency.
Only a few years before, the western coast of North America was nearly unknown territory. The first European ship to enter San Francisco Bay made its voyage in August 1775, when Lt. Juan Manuel de Ayala brought the Spanish navy ship San Carlos though the Golden Gate. Ayala, who tried to come in on the ebb tide, had a terrible time -- at one point the current was so strong his ship seemed to be going backward.
When the U.S. coast surveyors came to California in 1849, they found that some of the charts of major headlands -- Point Conception and Cape Mendocino, for example -- were off by as much as 15 miles, and the tidal actions at the entrance to San Francisco Bay, the biggest and most important harbor, were poorly understood. There were 26 major shipwrecks on the approaches to the Golden Gate in a four-year period ending in 1854. Many of them were due to errors of navigation or misunderstanding of the currents.
The first tidal observations were made at Rincon Point -- near the site of today's SBC Park -- and Sausalito. For various reasons, these were unsatisfactory, and on June 30, 1854, the station was opened at the Golden Gate.
Only six months later, on Christmas Eve, the station observed a series of "sinusoidal squiggles" on the tidal register. These were different from the regular tidal movements and intrigued Army Lt. William Trowbridge, an Army officer detached for duty with the Coast Survey. In early 1855, Trowbridge wrote headquarters in Washington to say he thought the squiggles were from a tsunami caused by an earthquake that had occurred somewhere, possibly under the ocean floor.
There were no seismographs at the time, but it turned out that the quake had occurred in Shimoda, Japan, on Dec. 23, 1854. Japan at that time was still in the age of the samurai, and word of the quake took months to reach the outside world.
But it had a major impact on understanding the natural world. By comparing the distances from Japan and the observations of the tsunami's arrival in San Francisco, the Coast Survey's chief, Alexander Bache, was able to estimate the average depth of the Pacific Ocean.
Modern technology showed his estimate was off only by 10 percent.
Over the years, the gauges also showed a gradual rise in the sea level -- eight inches in 150 years. However, there was also a period of 38 years, ending in 1913, when the sea level declined.
The San Francisco gauge also measured other phenomena -- such as the effect of the El Nio condition on water levels. The highest tide ever recorded was on Jan. 27, 1983, when the surface of the water at the Golden Gate reached 8.78 feet above mean sea level, or zero. The lowest tide was on Dec. 17, 1933, with minus 2.9 feet. The 1983 high tide accompanied a downpour associated with the El Nio condition; the lowest accompanied a period of the exact opposite condition.
The normal tidal range is about 5.8 feet, more when the moon is full. The tide also affects the currents in the bay, which are strongest in the Golden Gate, and in the San Pablo and Carquinez straits.
Sometimes, the currents in the Gate can reach well over six knots, particularly on an ebb tide. Millions of gallons of water flow in and every day: there are two high and two low tides a day. Various machines, from simple clockwork recorders to digital computers, have been used to record the rise and fall.
Most modern ships are powerful enough to sail on any tide, given sufficient water depth. But for the small boats, the currents and tides are as crucial as they were in the days of the old Spanish sailing ships.
The rise and fall of the tides four times a day in San Francisco Bay is "like a living thing'" to Peter Evans, who is 74 and has been rowing on San Francisco Bay and its tributaries for 45 years. The salt water, he says "moves in a slow pace, like breathing."
Evans, who sometimes rows from Bolinas, on the Marin coast, to Alameda, must use the tides to help him make his way on the water.
"Just outside the Golden Gate on a big ebb tide there is a big upsurge," said Evans. "When you hit it, it is just like a car, sliding on ice."
Evans liked to calculate the tides himself. He still does it the old-fashioned way, using the tide tables, and his sense of what the water is doing.
"If you are successful, it is sort of a game," he said. "The water doesn't always do what you think it will do. It has a timetable all its own."
-------------------------------
The anniversary
The National Oceanic and Atmospheric Administration will commemorate the 150th anniversary of tidal observations at the Golden Gate on Wednesday with an exhibit on the tides and presentation of the NOAA environmental hero award to Pietro Parravano, former president of the Pacific Coast Federation of Fishermen.
The ceremony begins at 5:30 p.m. at the San Francisco National Maritime Historical Park Visitors Center, at Hyde and Jefferson streets. The featured speaker will be vice admiral Conrad Lautenbacher, NOAA administrator.E-mail Carl Nolte at [email protected].
GRAPHIC: PHOTO (2), (1) The tide house at the Presidio, smaller of the two buildings, sits at the end of a pier near Crissy Field. / Mark Costantini / The Chronicle, (2) The Golden Gate Bridge towers above the humble tide house, which has been in continuous operation since June of 1854. / Mark Costantini / The Chronicle
LOAD-DATE: June 28, 2004
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