Ecological rewind

Environmentalists want to tear down O'Shaughnessy Dam and restore the Hetch Hetchy Valley, but does their plan hold water?

Kolana Rock towers above Hetch Hetchy Reservoir in Yosemite National Park.

Follow the trail from Yosemite National Park's Rancheria Falls up along dusty switchbacks and down through a canopy of pines and madrones for roughly three miles, and you will reach Tiltill Valley.

Accessible only to hikers and horseback riders, the backwoods meadow hums with the chatter of birds, bees, and the distant rush of water spilling over rocks. Butterflies dart among wild orchids, lilies, yarrow, and other kinds of flowering plants that thrive there, and a lone sequoia stands along the perimeter. The valley floor is lush and boggy, with the forested hills of the High Sierra as its backdrop.

Tiltill Valley is a real-life example of what Yosemite's Hetch Hetchy Valley might look like if the reservoir that holds San Francisco's water supply were drained and the terrain allowed to return to its natural state, according to Mike Marshall, executive director of Restore Hetch Hetchy.

His nonprofit group has a singular mission, as the title suggests. The upbeat, 50-year-old former political consultant wants to place a charter amendment on the November 2012 ballot to ask San Francisco voters if Hetch Hetchy Reservoir should be drained so that the valley, which has been underwater since 1923, can be ecologically restored and turned into an attraction for park visitors.

Yet that simply stated goal belies an extraordinarily difficult and expensive task, one that would fundamentally alter San Francisco's water delivery system and diminish a city-owned source of inexpensive, green energy.

"The destruction of Hetch Hetchy Valley in the 1920s was the worst environmental disaster to ever besiege the national park system," Marshall says. "And today, it is completely out of whack with the values of the vast majority of people who live here."

But most city officials think this idea is just plain crazy. Whether or not it was a good idea to build the dam originally, they say it's unwise and unrealistic to spend scarce resources to destroy one of city's most valuable assets.

"While it is an interesting idea, I don't think that there is yet a credible plan to move forward and actually restore Hetch Hetchy that will ensure that within our budget, we'll be able to get the water that 2.5 million Bay Area customers need, as well as do everything else that the current Hetch Hetchy system does," Board President David Chiu told the Guardian.

Based in San Francisco, Restore Hetch Hetchy worked in tandem with the Environmental Defense Fund and a consulting firm to craft a technical analysis describing how the city could continue receiving reliable freshwater deliveries without the reservoir, although it would require filtration because of its lower quality and be less abundant in drought years.

While restoring the valley would be an ecological win in a perfect world, cost estimates range in the billions of dollars at a time when budgets are shrinking and economic turbulence rocks the public and private sectors.

Draining Hetch Hetchy Reservoir and replacing it with other water and power projects would punch holes in an already cash-strapped city budget, first with the high capital costs and then with higher long-term annual costs. The hydro-electric system provides carbon-free electricity to city agencies at basement rates and helps fund local renewable-energy projects, so relinquishing some of that generation capacity would be a step backward when it comes to addressing climate change.