More on Yosemite Hetch Hetchy Discussion

It may be a day late and a dime short, but I received this comment from Ronn Coldiron, PhD, of Walla Walla Washington. Ron is a Geologist and has studied the idea of removing the O’Shaugnessy Dam and storing the water San Francisco needs downstream. If you can take the time to read it (warning – long attention span needed), you may agree. He’s run his ideas up the flagpole, but it got nowhere. The citizens of SF voted down the study of the issue, but the Restore Hetch Hetchy group is not rolling over.  The fight is a century old, but the match is not over.

Restoring Hetch Hetchy Valley: A New Approach

Dianne Feinstein was quoted in the Sacramento Bee recently, “There is simply no feasible way to replace the Hetch Hetchy Reservoir, return the valley to its original condition and still provide water to the bay area.” I disagree with the Senator in that not only can all these conditions be met with the removal of O’Shaughnessy Dam, but the Hetch Hetchy system’s water filtration avoidance classification can be maintained and provide close to the same amount of power now provided to the Bay Area. In other words, there is a change to the current water system which will allow the restoration of Hetch Hetchy Valley and will come very close to making the current stakeholders whole.

Making the current stakeholders whole is critical, because previous plans proposed to drain the Hetch Hetchy Reservoir require loss of filtration avoidance, water shortages and a significant loss of hydroelectric power generation. Faced with this type of alternative, naysayers will most likely keep the upper hand.

The most critical shortcoming in current restoration plans is the loss of filtration avoidance, which would place the highest demands on the S.F. taxpayers. Under these proposals Hetch Hetchy Reservoir would be drained with no alternative storage. The result would be that most of the water currently stored in Hetch Hetchy Reservoir would enter Lake Don Pedro and would then have to be filtered like all other water in California.

The current proposal would have 5 major components:

1) Draining Hetch Hetchy Reservoir and removal of the dam, and restoring the valley floor;

2) Partially divert winter/spring flow of Tuolumne River water just above or below the current reservoir site and pump the Hetch Hetchy water over to the Eleanor– Cherry diversion Tunnel where it will be stored in Lake Lloyd (Cherry Lake).

Significant power savings can be had by building a diversion structure immediately upstream from the current Hetch Hetchy Reservoir and running a penstock under the valley floor, to a point just below the current dam site. The alternative would be to build an intake structure at the base of the current Hetch Hetchy Dam site and pump the water to Lake Lloyd via the Eleanor – Cherry diversion tunnel. This plan would leave the Tuolumne River completely wild and unrestricted in the valley but would require pumping the water uphill an extra 300 feet at considerable cost.

3) Divert all Cherry Creek flow around Lake Lloyd (or under the reservoir by penstock) to the base of the existing dam. If the dam were raised 40 feet, Lake Lloyd would have a maximum storage capacity of 340,800 acre feet or almost 95% of the current storage capacity of Hetch Hetchy Reservoir. With a very modest water conservation plan, the city of San Francisco would have more Hetch Hetchy water storage available than they do currently.

4) Hetch Hetchy water, when released from Lake Lloyd would be moved back downhill to the base of the current Hetch Hetchy dam site. The pumping facility required to lift and transport Hetch Hetchy water from the base of the Hetch Hetchy dam site would be partially offset by a powerhouse installed at the same location. The net loss would be due to inherent turbine/pump inefficiency and head loss due to pipe friction. One way this could be offset would be to divert Tuolumne River water just upstream from the upper reach of Hetch Hetchy Reservoir. This upstream diversion would be an inverted siphon and water would have to be pumped only 700 vertical feet to Lake Lloyd instead of 1000 feet. The return trip to the foot of O’Shaughnessy Dam would have 1000 feet of head for a significant net gain in power generation. If this is untenable due to environmental, political or other considerations, then at least 20% of O’Shaughnessy Dam’s current output of 615 mkwh per year would be used to transport water to and from Lake Lloyd.

In order for this plan to work, two critical issues would have to be settled:

  • · Could filtration avoidance of Tuolumne River water be maintained if stored in Lake Lloyd;
  • · Could a diversion structure be built to successfully bypass Cherry Creek around Lake Lloyd so as not to contaminate Hetch Hetchy water stored there. It is critical that a bypass structure be designed to insure capture of all Cherry Creek water during 50 and 100 year flood events.

5) The Cherry Creek water would be stored at Lake Don Pedro which would require the dam to be raised approximately 29 feet. If Lake Lloyd water is stored at Lake Don Pedro, the firm storage capacity of the current Hetch Hetchy water system would remain essentially unchanged.

One of the drawbacks of this proposal is the loss of power generation by eliminating the storage of Cherry Creek water at Lake Lloyd. Lake Lloyd would have a new role as the storage site of Hetch Hetchy water only. Power generation of Cherry Creek water would be limited to a run-of-the-river facility at the Dion Holm Powerhouse.

At present, the Dion Holm Powerhouse generates 810 mkwh of electricity annually with a rated capacity of 150 MW. With the loss of storage capacity at Lake Lloyd annual production would drop to 253 mkwh per year. The loss of electrical generation could be partially recovered by installing a new powerhouse at the base of Lake Don Pedro and would use Cherry Creek Water added to the reservoir. Cherry Creek water, if allowed to be stored there would increase storage by 268,800 acre feet. Assuming the same turbine rating of 810 cfs and approximately 500 feet of head the total power output would yield approximately 193 mkwh. This figure added to power generated at Dion Holm Powerhouse would result in Cherry Creek water generating 55% of current power production.

Currently, 1965 mkwh is produced by the Hetch Hetchy water system. With an inverted siphon used to help transport water from an undammed Hetch Hetchy Valley to Lake Lloyd, total power production would drop to around 1601 mkwh. This is an 18.5% decrease from current levels. This figure assumes no net gain of power if an inverted siphon is installed at the head of Hetch Hetchy Valley which is probably incorrect. A net gain of power would probably result in such an installation.

I believe this plan would be attractive to San Francisco voters because it would restore Hetch Hetchy Valley and would maintain water quality and water delivery with small decreases in power production.

The feasibility of this proposal will depend on answering many engineering, environmental and political questions. I encourage all interested parties; public agencies, industry and non-government organizations to work together to correct a tragic environmental mistake.

If you have any questions please contact me at rc@glencorrie.comor at my office at 925-831-1200.

Unrelated thought worth quoting: Not blind opposition to progress, but opposition to blind progress…” – John Muir

MrHalfDome™ – Rick Deutsch –

One Best Hike: Yosemite’s Half Dome

About Mr Half Dome - Rick Deutsch

Mr Half Dome. Has written the only half dome hiking guide, One Best Hike: Yosemite's Half Dome. Has hiked it 31 times to day. Lives in San Jose, CA Available for presentations. Carpe Diem Experience, LLC
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One Response to More on Yosemite Hetch Hetchy Discussion

  1. Maueen L says:

    Also in the news here in the Bay Area is great concern about coming decline in Sierra snowpack and other issues about California’s water needs. Needs of agriculture, even if they start using methods that use water wisely, are a big part of the issue.

    It’s a global problem for all who rely on snowpack for summer water.

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