Hetch Hetchy: Will We Do the Anthropocene Thing?
Topics: Blog, Engineering, Geology, Water
San Franciscans this fall will be asked to vote on the Water Sustainability and Environmental Restoration Planning Act, a scheme that aims to put the cost of civilization in sharp relief. In essence it asks, Do we want to arrange our society as if nature really matters?
Every great city relies on a great water supply, from ancient Rome to San Francisco. The Hetch Hetchy system was beautifully designed and built, except that it destroyed a nearly unique valley inside Yosemite National Park. The nonprofit organization Restore Hetch Hetchy (RHH) wants San Franciscans to weigh the price of doing things better, according to a specific definition that includes pulling out of the park.
The Hetch Hetchy Water System begins with a dam and reservoir that traps some of the world's cleanest water in a basin of Sierra Nevada granite.
Tunnels and pipelines carry Hetch Hetchy water to the Bay Area entirely by gravity, with some of that gravitational energy turned to electricity along the way.
The Hetch Hetchy Water System is a colossal engineering triumph that has provided not just San Francisco, but many Bay Area cities, with clean and reliable water for nearly 90 years.
The Hetch Hetchy Water System still performs to specifications, but RHH argues that today we could make it work while sparing Hetch Hetchy Valley and removing its reservoir. That may be so, and the few million dollars required for a good study and action plan would be well spent because previous efforts have been sketchy. RHH is rolling the dice by forcing the plan, whatever it is, to be considered by the San Francisco Board of Supervisors for placement as a charter amendment in the 2016 elections. That is, if the Supes vote it down, nothing will come of it, but if both they and the city's voters approve it the plan will go into effect willy-nilly.
Dam removal is a growing endeavor, and one of great scientific interest, because so many of the nation's dams are reaching the end of their lives. This happens when the reservoirs behind them fill up with sediment. The most recent success in dam removal is the Elwha Dam project in Washington state. In that case, the reservoir had silted up. O'Shaughnessy Dam is more than 30 times as large as Elwha, its reservoir is far from being silted up, and the dam isn't sited on an earthquake fault. From an engineering standpoint, there's no rush.
RHH's plan is a visionary scheme based on environmental justice, appealing as an example of eco-responsible, sustainable practice. But are we better off with the dam gone now? Conversely, if we really are in an "Anthropocene age" when we can influence the entire planet by our actions, shouldn't we begin to act accordingly? Shouldn't we begin geoengineering?
The obstacles to RHH's plan are great, but I believe the group is playing a very long game. The Hetch Hetchy system is exceptionally stable because the reservoir is many centuries away from filling up with sediment. As time goes on our ability to engineer the water system intelligently will only improve. As a geotechnical matter, that slow pace of sedimentation means that Hetch Hetchy Valley can indeed be restored. By putting the question to a formal evaluation, RHH hopes to ensure that restoration will be on the agenda for as long as it takes.Tags: anthropocene, california department of water resources, geoengineering, hetch hetchy, yosemite