A dam difficult job

California’s drought through the eyes of a water manager.

  • Water managers found dismal snowpack at Bond Pass in February. In normal years, they strap on their skis to monitor snowpack that will feed into Hetch Hetchy Reservoir.

    Courtesy San Francisco Water, Power and Sewer
  • Tueeulala Falls, upper left, and Wapama Falls, middle right, fill Hetch Hetchy Reservoir behind O’Shaughnessy Dam.

    © Marty Bicek/TheModesto Bee/Zuma

Late last January, under clear skies, a helicopter dropped Adam Mazurkiewicz and a coworker in a high meadow in the Sierra Nevada north of Yosemite National Park. They were there to check the depth of the snowpack and the amount of water it held, at places they visit every month throughout winter, year after year. Normally, they would have skied some 30 miles in the next four days. But this time, instead of several feet of snow, they saw only patches between brown grass and bare soil. Mazurkiewicz left his skis in the helicopter.

He was disappointed, and not just because he would miss a ski day. Mazurkiewicz is the reservoir operator at Hetch Hetchy Reservoir in Yosemite. His job is to work with a team from the San Francisco Public Utilities Commission to fill the reservoir. If they’re successful, 2.6 million people, plus businesses, in the San Francisco Bay Area are assured a reliable source of water to drink, flush their toilets, and keep their lawns green. The last time the reservoir failed to fill was near the end of another severe, multi-year drought. Operators released too much water for hydropower, and in 1991 the reservoir hit one of its lowest levels ever. Residents had to ration their water.

Hetch Hetchy provides 85 percent of the water in San Francisco’s eight water storage reservoirs, and nearly all of it comes from snowmelt. Trudging across the naked Sierra Nevada, where snowpack this year reached only 18 percent of normal, Mazurkiewicz was concerned. Over the next four months, he would have to find some way to harness this pitiful snowpack to keep the Bay Area wet while saving as much water as possible for next year. That would mean keeping an unwavering focus on runoff, anticipating its every fickle move.

Reservoirs, it’s worth remembering, don’t fill themselves. Even in years when snow is plentiful, topping off Hetch Hetchy takes work. Often, more water melts off the mountains than the reservoir can hold, and Mazurkiewicz and his coworkers have to figure out what to do with the excess without letting so much go that, when runoff ends, the reservoir isn’t full. It’s a delicate balance, achieved in part by expecting the worst. “A water-supply operator’s job is to be a terrible pessimist,” says Bruce McGurk, a past operations manager at Hetch Hetchy, “and figure that next year is going to be worse than this year, so that you are prepared” — by banking as much water as possible.

Even for a professional pessimist, the sight of bare grass at 9,200 feet in January was sobering. It made an already-tough job seem impossible. Mazurkiewicz never knows exactly how much snow sits above Hetch Hetchy, how much water it will yield, or when it will melt. (Weather forecasts are imperfect, and data points on snow depth are sparse, providing an incomplete picture.) So he and other forecasters rely on what they know happened in the past to create statistical equations that model the future.

But this year, one of the worst snow years on record, Mazurkiewicz thought, “My statistical models will not be useful.” Back in the office, his team had to develop new models and accept larger errors in their forecasts. After the January outing, their models projected a 60 to 70 percent chance of the reservoir filling.

So even after two storms helped bring February’s precipitation up to normal, Mazurkiewicz kept every drop of water left over from last year. In a wetter year, he would have released water to produce hydropower and make room for runoff. This year, his team nixed most hydropower and skipped ecological experiments that would have provided the Tuolumne River with higher-volume spring pulses to boost aquatic life and wetlands. Such situations could become more common, says McGurk: “If our historical data are less robust for future (forecasts) because of changing climate, operators will have to hedge more and operate more conservatively.”

Mazurkiewicz had little hope for a “miracle March,” when big snowstorms often unleash over the Sierra, rescuing Californians from potential water shortages. This year, he wished merely for a “median March,” and didn’t get even that. April was more of the same: a couple of anemic storms, but no weeklong whoppers. A colleague in Utah once compared such situations to being served quiche when you’re craving steak and eggs. “It could tide you over,” Mazurkiewicz says, “but it was certainly not enough.”

Then, in May, the weather changed; light snow fell every week and rapidly melted into the reservoir.  In a normal year, Mazurkiewicz and his colleagues carefully calculate when to release water through hydropower turbines, doing it gradually so that an unexpected surge of runoff — caused by a sudden spell of hot weather, for instance — doesn’t spill over the dam, flooding the river. This spring, they didn’t think they’d have to do that. But with May’s storms, they decided to move water to another reservoir to make room in case the runoff exceeded expectations. It turned out to be a wise bet: By mid-June, the reservoir had risen to within about a foot and a half of full, surprising everyone.

Given the state’s overall water shortage, however, Mazurkiewicz and his colleagues didn’t celebrate. They simply gave thanks for what they had, well aware that it wouldn’t last. The reservoir typically hovers at its peak for two weeks as new snowmelt comes in. This year, it began falling within a day. By August, all Californians were under strict mandatory water-use restrictions. 

Reached by phone in his office in August, Mazurkiewicz was already thinking about next winter — and planning for a fourth year of drought. Though Hetch Hetchy is normal for this time of year thanks to water conservation, the entire regional system of reservoirs is at just 62 percent of capacity. And if moisture does return suddenly, Hetch Hetchy could face a new set of problems, like flooding. Nearly filling the reservoir was satisfying, but only fleetingly. “We may celebrate when we have enough snow on the ground to refill the entire system,” Mazurkiewicz said wryly. “Hopefully, flood planning does not interrupt that.”

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