Watching the Tides Educator Guide

Ocean tides rise and fall twice a day, influenced by the gravitational forces of the sun and moon. Studying tides' rhythmic movements helps us understand both the ocean and the cosmos. Astronomer Ben Burress explains how tides work, and QUEST visits Crissy Field in San Francisco to see the oldest continually operating tidal gauge in the Western Hemisphere.

Sittin' on the dock of the bay, watchin' the tides roll away.

This is important because the bay and ocean currents flooding in and out of the Golden Gate are notoriously treacherous.  The US Government realized early on the importance of San Francisco Bay and the need to better understand the movements of the water for navigation.  Soon after California became a State, American surveyors were sent to San Francisco to study the water conditions of the great port.  And the work has continued non-stop ever since.  For over 150 years the San Francisco Tide Station, now operated by NOAA, has produced a continuous recording of water levels and other vital maritime information.

Today the tide station uses state of the art equipment to measure the water movement of San Francisco Bay. The water gauges are connected to the NOAA Physical Oceanographic Real-Time System (PORTS), and measure nearly real-time water levels, surface and sub-surface currents and other information such as winds, weather and climate data.  This information is available to the public so sailors know the best times to cast off, make transits, load or unload cargo, or when to ride the tides in or out of the bay.  According to a report written by Captain Albert E. Theberge, NOAA (Ret.), “This information is critically important considering that there is an average of 261 deep-draft vessels entering San Francisco Bay each month and there are approximately 85,000 registered pleasure boats using approximately 100 yacht clubs in the Bay system.”

“The historical record from the tide station at San Francisco transcends the maritime history of the San Francisco Bay,” according to Captain Theberge.  “From the days when clipper ships relied upon tide predictions provided by the station to navigate the dynamic waters of the Golden Gate, to the modern day mariner that obtains real-time water levels so that the huge ship and crane barge operators can tell if they have enough depth in the channels and enough clearance under the bridges.”

In the process of collecting data to insure safe passage in and out of the bay, the San Francisco Tide Station has been instrumental in collecting a long and continuous stream of scientific data that has advanced our knowledge of the oceans and the earth. This data has benefited meteorologists, oceanographers and climatologists alike.  As we look to the future and attempt to better understand the changing climate and what that will mean to things such as sea level rise, the current and long-term data collected at this small station will become increasingly more important.  “San Francisco is an amazing city in terms of its heritage,” says Mary Jane Schramm, “ The human heritage as well as the magic and mystique of the great Golden Gate.  It’s a portal for exploration.  We are explorers and by virtue of having this facility here helps foster that process along.”

37.8035713 -122.4593512

Oil booms at Crissy Field. Credit: fredsharples

It seems that the fate of birds in these situations provokes an especially emotional response in most people. Maybe it’s their visibility, maybe it’s the metaphor of losing flight, but there’s something about an oil-covered bird that makes plain the most tragic consequences of human interactions with nature.

Standing at the beach (which I visit frequently because it’s across from my office) made me realize how much there is to understand about the Bay’s inner workings. Knowing that there was much less oil on Crissy Field than at Rodeo Beach made me consider how the Bay’s currents flow than I had before. The booms floating in the water prompted questions about whether marine microorganisms are filtered out along with the oil, what role such critters play, and how they’re faring in an oily environment. Watching ducks splash about in the marsh, I wondered about the less-visible fates of the plants and fish below the surface. No doubt the oil spill's effects are beyond birds and oily blobs on the beach, hidden to those of us unfamiliar with the Bay’s ecosystems and mechanics.

While Craig and I meandered the dunes with Park Service staff days before, we learned that Crissy Field is an ever-changing environment, always in flux, sometimes through forces of nature and sometime at the hands of humans. Remembering this was heartening. Crissy Field has gone from natural shoreline to air strip and back to shoreline again, and has recovered from past oil spills much larger than this one. Nature (with a little help from concerned citizens) has amazing repair mechanisms, and has allowed Crissy Field to survive many assaults during its history. Despite its current scars, it will survive this as well.

Robin Marks is a journalist and science writer who current serves as a Multimedia Projects Developer for the Exploratorium in San Francisco, CA.

latitude: 37.8058, longitude: -122.4530