Tuesday, June 7, 2011

After Lightfoot: Restoring the Hetch Hetchy Valley

O’Shaughnessy Dam and Hetch Hetchy Valley

After the exciting conclusion of THE MIGHTY T, I wrote a brief chapter that addressed several things. One was what happened to the Hetch Hetchy Valley after the terrorist John Lightfoot successfully destroyed the O'Shaughnessy Dam. Here is a excerpt from that chapter:

There were two camps of thought concerning the restoration of the Hetch Hetchy Valley. While they differed on everything else, they had agreed on a set of eight givens.
To create a solid base for the dam, Michael O’Shaughnessy had had to excavate 118 feet below the natural riverbed. If they removed all 118 of concrete, the river gradient would be too steep and the valley would quickly erode.
So the first given was, leave enough of the dam in place to restore the original stream gradient.
Sediment accumulation behind a dam is a major problem; it displaces water and is a huge environmental mess when the dam is removed, which all dams eventually will.
The second given was, Hetch Hetchy lacked sediment. The watershed forming the Tuolumne River is mostly granite rock, cut and formed by glaciers, covered with a thin layer of soil — there was little to wash into the valley. What little sediment there might have been over the years had already washed downstream because water was released from the bottom of the dam.
The second given leads into the third: because of the lack of sediment buildup, the original river channel still exists. Restorers didn’t have to worry about dredging a new channel, which they would have had to do if the valley was full of silt.
No one knew for sure what native flora and fauna existed in the Hetch Hetchy Valley circa 1920, but — the fourth given — whatever would’ve been living in the valley had the City of San Francisco not flooded it, probably still lived in the mountains and valleys around Hetch Hetchy. It was assumed these native plants and animals would, with time, find their way back into the valley.
The fifth given was simple: it would be impossible to prevent non-native plants from taking root. Yosemite Valley had forty-five non-native types of grasses, so it was silly to think Hetch Hetchy wouldn’t also.
The sixth given was, bugs and worms will return on their own.
Seventh given: no one knew what to do about the white bathtub ring around the valley, so they would have to be content to let nature figure it out.
Eighth and final given: little creatures might need help if there were too many bigger creatures around eating them. Everyone thought it would be okay to meddle by bringing in more little creatures, or removing a few big ones.

(This information came from a 1988 National Park Service study; I wanted the book to be as accurate as possible, keeping in mind it’s a work of fiction.)

The chapter also discusses two camps of thought regarding how the restoration should be managed: one camp says, keeping in mind the above givens, give Hetch Hetchy back to nature and let her make of it what she will. Man screwed it up in the first place by flooding the valley so he should keep his soiled hands off the restoration.

The second camp wants to micromanage the restoration and is split into two subcamps; some for managing with a light hand, others with a heavy hand. Those in favor of light management think it would be okay to meddle a little by replanting fora and re-populating fawna native to the area; give nature a helping hand.

Those who favor the heavy-handed management want to control everything. They would erect greenhouses and nurseries while the valley drained, then map out where everything would be planted. Then they would micromanage the valley forever.

All sides think Hetch Hetchy would, in 150 years, look like it would have had the City of San Francisco not flooded it in 1923. Except, of course for the fifty-foot white ring around the valley where the pure water had leached minerals from the granite mountains. It can be erased only by hundreds or thousands of years of erosion.

I’m not sure I agree. In all likelihood, the Hetch Hetchy Valley would have been developed in a similar manner as its big sister, Yosemite Valley. No doubt someone would have erected a hotel or two, paved roads would’ve been laid, and tourists would’ve been motoring through the valley, dirtying up the air.

A restored and protected Hetch Hetchy, save for the bathtub ring, might be an improvement on what might have been had man not intervened.

Albert Bierstadt's painting of Hetch Hetchy Valley