Bring Hetch-Hetchy Valley Back?

Norimitsu Onishi of the New York Times reported on an upcoming city-wide ballot measure in San Francisco to dismantle the Hetch-Hetchy Reservoir and restore the valley. Currently the reservoir, which is formed by the 364-foot O'Shaughnessy Dam, stores 360,000 acre-feet of San Francisico's drinking water supply.

Many city officials and opponents to the restoration question whether adequate water can be found elsewhere, and balk at the potential cost of decommission and ecological restoration ($1-$10 billion, depending on who you ask). Other considerations include impacts to hydropower generation and agriculture.



The valley currently submerged under the reservoir is very similar to nearby Yosemite Valley. When the dam was proposed, it was heavily opposed by activists and early environmentalists, most notably John Muir, who said, "Dam Hetch Hetchy! As well dam for water-tanks the people's cathedrals and churches, for no holier temple has ever been consecrated by the heart of man." Despite the opposition, the dam was constructed in 1923. Decommissioning it was not a visible issue until the last 2 or 3 decades.

San Francisco has long struggled to supply enough water to its growing urban population. The Hetchy-Hetchy Reservoir system, which includes O'Shaughnessy and ten other dams, is responsible for bringing drinking water to 2 million users. The O'Shaughnessy Dam currently stores 25% of the capacity of the entire system. It also has the advantage of filtration avoidance because the water quality is very high. If it were decommissioned, water users would not only incur costs from finding other water sources, but also from increased filtration costs.

The arguments for decommissioning the dam are also based in economics. The increased recreation opportunities would bring in valuable tourist dollars and alleviate the impact currently borne by high visitation rates in Yosemite.

The possible outcomes from dam removal were the subject of a recent thesis. The author determined that storage capacity for the system would be substantial without the dam, especially in dry years, but that full delivery of water to users and environmental uses would still occur.

Perhaps the most interesting part about this story is that it will be the people of San Francisco, not engineers, scientists, or planners, that will make the decision.