Visiting San Francisco Bay, in a warehouse

U.S. Army Corps of Engineers' Bay Model is a wonder of watershed sims, even after computers replaced it. Photos: A model bay

SAUSALITO, Calif.--Because I don't have my own airplane, and I can't afford to fly commercial all the time, it's really cool to have the ability to calmly check out the entire San Francisco Bay from 12,000 feet anytime I want.

No, I don't have a helicopter either, and I can't fly. Actually, what I have--as does anyone else--is easy access to the Bay Model, a wonderful, two-football-fields-long simulation of the entire bay and all the surrounding waterways that is run by the U.S. Army Corps of Engineers.

Known officially as the San Francisco Bay-Delta Model, this project--which is housed just across the Golden Gate Bridge in a three-acre building here that formerly served as the warehouse for one of the largest World War II-era shipyards in the country--is all about studying the effects of humans on one of the most important watersheds in the West.

According to my tour guide, Corps of Engineers senior ranger Bill Cope, the model was funded by a congressional grant of $400,000 in order to study the so-called Reber Plan, the brainchild of theatrical producer John Reber, who had proposed building two giant fresh-water plants and associated dams in the bay in order to guarantee, in perpetuity, fresh water for the region.

The plan was eventually rejected for the nonsense that it was, but the Corps of Engineers and Congress thought it interesting enough to want to simulate its effects. And because they didn't have computers that could do it, they built the Bay Model.

It was constructed in 1957. And although the public could visit--free of charge, as it still is today--its primary purpose was as a research facility. There, scientists, mathematicians and engineers were able to study how humans impact the San Francisco Bay-Delta, the West Coast's largest estuary, which comprises about 1,600 square miles of waterways and which drains more than 40 percent of California's entire fresh water supply.

Indeed, while the fresh water is created in the northern part of the state from snowfall in the Sierras and other mountains, more than 50 percent of it is siphoned off via a vast aqueduct system to Southern California.

Government officials decided back in the 1950s that it would be a good idea to study how the Sacramento and San Joaquin rivers flow into the tangle of islands, sloughs, canals and channels.

How important is it all? Fully two-thirds of California's homes and farms depend on the flow for fresh water.

Given that I grew up in San Francisco and have lived most of my life in the area, I had visited the Bay Model once, long ago. It's the kind of place that draws 150,000 visitors a year, with up to 75 percent of them being schoolchildren. I had been one of them, though I hadn't paid much attention to the details.

So I was surprised to discover, for example, that Sausalito had been home to such a giant shipyard, commissioned in 1942 by President Roosevelt. At its peak, the shipyard employed 22,000 people working on six giant vessels at a time.

Every 3.8 minutes, the tide turns. First it comes in, and then it goes out, and then it repeats. And there's your full day.

What I do remember, though, is being blown away at this giant model of my beloved bay. My memory may not have gotten it quite right--for example, I recalled it being deep in many areas, while in fact almost the entire model is less than a half-inch of water deep--but upon visiting it this week, I was no less impressed.

You walk into the Bay Model--the nation's only operational hydraulic model--on a second-story walkway that was built in 1981. First you go through a series of exhibits and films that were added in 2003, and then you emerge into the interior of the giant building, feeling like you're lording over the bay. After all, a sign informs you, your vantage point is the equivalent to being 12,000 feet over the real water.

Because the Bay Model is a scale version of the real thing, it has to compress reality. So, it is designed to simulate a single real-time day in just under 15 minutes. That means that in less than every four minutes, the tide turns. First it comes in, and then it goes out, and then the cycle repeats. And there's your full day.

You can't really see the effects of these tidal changes, but, Cope explained, if you look at the water where light is reflecting on it, you can see which direction the water is moving, and that tells you whether the tide is heading in or out.

Until 2000, the Bay Model was still used as a research facility. But starting in that year, thanks to the Corps' acquisition of supercomputers that can do the necessary simulations, researchers no longer needed the site for scientific study. Since then, it has been used strictly for education.

Indeed, one sign informs visitors with no irony intended--but much received, by me at least--"Today, the only water involved in modeling the bay is in the drinking glass of a person operating the computer."

Ah, progress.

Nevertheless, the Corps of Engineers has no intention of closing down the Bay Model, and in fact, it is humming right along on its $1.1 million of Corps of Engineers general funds.

Ultimately, it is an engineering marvel. It is built on a horizontal scale of 1,000-to-1, and a vertical scale of 100-to-1. Cope explained that its sump tank holds 185,000 gallons of Sausalito tap water, and that it takes 135,000 of those gallons to flood the entire model.

In the morning, the model's operators flip a switch, and around 20 minutes later, all 135,000 gallons have filled the model. At the end of the day, they turn off the pumps and eventually, all the water flows back into the sump tank.

The model also has some charming features like a little Golden Gate Bridge, as well as small versions of the Bay Bridge and all the other major bridges in the area. No word yet on whether they will put in a new scale model when the new eastern span of the Bay Bridge opens in 2013.

There's also a small model of San Francisco's baseball stadium which, for some reason, is enclosed in a glass case. Perhaps they were afraid someone would steal it after Barry Bonds broke the home run record?

To Cope, this is the "Bay Model Miracle," because the whole thing still works. The Corps of Engineers doesn't give the facility extra money for maintenance, and so any repairs are done with in-house funds.

And while it is still fully functional, it is showing signs of aging. All around the model, on its floor, are little rust marks that have appeared over the years because of the rebar used in its concrete construction.

And as for how long it is expected to last? Well, no one knows, Cope said.

"Our engineer thinks it could go on for years and years," he said, noting that it's just a guess.