Not one drop of water supply need be lost in restoration

Yosemite National Park can be made whole, San Francisco gets its water

Since our inception, Restore Hetch Hetchy has always been committed to water supply solutions for San Francisco and all communities that rely on the Tuolumne River. To be very clear, we have adopted the mantra "not one drop need be lost".  

San Francisco's water rights will not change. The City will still store water in eight other reservoirs.
New interties to existing water storage in Cherry or Don Pedro Reservoir will allow 95% of the San Francisco's existing supply to be retained.
Modest new investments in groundwater, local surface storage, recycling or water transfer programs will keep San Francisco whole. Other California communities have done much more.



Yosemite National Park's Hetch Hetchy Valley, before being dammed and flooded by San Francisco.

(Photo: Isaiah West Taber, 1908)

Restore Hetch Hetchy's legal petition, filed in Tuolumne County Superior Court, alleges that the value of restoration far exceeds its cost - a cost that includes assuring all water supply is replaced. Our petition also recommends that San Francisco be afforded adequate time to implement water supply improvements before Hetch Hetchy Reservoir is emptied and restoration begins. So there is absolutely no reason to fear that restoration will cause any shortages to San Francisco's Regional Water System.

Ultimately, it is San Francisco's job to develop and implement a final plan. In our view, however, there are three important elements for San Francisco to maintain or improve water supply reliability when Hetch Hetchy Valley in Yosemite National Park is restored.  

  1. The Existing System: When Hetch Hetchy Valley is restored, San Francisco will retain all its water rights, its other eight water storage reservoirs, and its existing pipelines and tunnels. The Tuolumne River will remain the predominant source of San Francisco's water. Hetch Hetchy Reservoir is a storage tank - one of nine in San Francisco's system, and its function can be replaced. 
  2. New Interties: San Francisco will install new interconnections between its pipelines and Charry and/or Don Pedro Reservoirs - its other storage facilities in the Tuolumne River watershed. With these interconnections, the vast majority of Tuolumne water would then be available. 
  3. Modest New Supplies: San Francisco will develop modest new supplies through groundwater development or banking, reservoir enlargement, recycling or long-term purchases. Since 1990, other California water agencies have developed enough water through these programs to replace Hetch Hetchy Reservoir more than 19 times over.

The Existing System 

San Francisco owns and operates a water system that sells water to residents and businesses within the city, as well as to other Bay Area cities, including most of San Mateo County and parts of Santa Clara and Alameda Counties. About 85% of this water is imported from the Tuolumne River watershed, while the remaining 15% of the water is derived from local watersheds in the Bay Area. See Figure 1.


Figure 1 - San Francisco Regional Water System  


Figure 2 - San Francisco's surface water storage. 

Restoring Yosemite's Hetch Hetchy Valley will not affect San Francisco's water rights on the Tuolumne River. San Francisco will also continue to store water in 8 other reservoirs, generate hydropower at its powerhouses, and retain its system of tunnels and pipelines for conveying Tuolumne River supplies to the Bay Area.

Hetch Hetchy Reservoir is one of 9 reservoirs in San Francisco's Regional Water System, and accounts for about 25% of its total surface storage. Hetch Hetchy Reservoir accounts for only 1/8 of the surface storage in the Tuolumne River watershed. San Francisco paid one half the cost of constructing Don Pedro Reservoir, located downstream on the Tuolumne River. Don Pedro is owned and operated by the Turlock and Modesto Irrigation Districts but includes a water bank for San Francisco that can hold between 570,000 and 740,000 acre-feet of water, depending on flood control criteria.

For a more complete description of San Francisco's Regional Water System as it exists today, see chapter 5 of Paradise Regained: Solutions for Restoring Yosemite's Hetch Hetchy Valley, Environmental Defense Fund, 2004

New Interties

Without Hetch Hetchy Reservoir, San Francisco will still be able to divert Tuolumne water supplies at Early Intake - just downstream of the Kirkwood Powerhouse - during times of year when the river is flowing. This is the same location where water is presently diverted from the Tuolumne River into the Mountain Tunnel, and eventually to the Bay Area.

During summer and fall, when the Tuolumne River has insufficient flow, San Francisco would divert water stored in Cherry, Eleanor or Don Pedro Reservoirs. To make these diversions possible, San Francisco would install one or more new interties (see Figure 3). San Francisco itself has considered building an intertie to enhance its access to supplies stored in Cherry Reservoir.


Figure 3 - Potential locations for one or more additional interties to assure San Francisco access to supplies stored in the Tuolumne watershed.

Building an intertie to access its water supply stored in Don Pedro Reservoir would require cooperation between San Francisco and the Turlock and Modesto Irrigation Districts. Presently, the sharing agreement between San Francisco and the Districts precludes such an intertie. Restore Hetch Hetchy, however, is confident that a mutually beneficial arrangement can be reached, in part because San Francisco paid half the cost of constructing Don Pedro Reservoir.

For a brief comparison of the potential performance of various interties, see Tuolumne Watershed Diversions without Hetch Hetchy Reservoir: Comparison of Interties to Cherry and Don Pedro Reservoirs, Environmental Defense Fund, 2005.

With an intertie to Cherry or Don Pedro Reservoir, almost all Tuolumne River supplies would be maintained (See Figure 4). Only modest additional investments would be required to ensure equivalent reliability in the driest years. 


Figure 4 - San Francisco Regional Water System reliability with one or more new interties, before development of new supplies. Note almost all Tuolumne River water would still be available, but some new supply, especially in dry years, would be required.

Modest New Supplies

Over the last 25 years, other California urban water agencies have developed more than 19 times the amount of water required to accommodate the restoration of Hetch Hetchy Valley. These agencies have invested in a combination of surface storage, groundwater storage, water purchases and water recycling programs. The supplies derived from these investments have often improved the environmental performance of urban water systems and reduced the impacts of those systems on California's rivers and wetlands.

Replacing the water supply reliability that would be lost by eliminating the 360,000 acre-feet of storage currently provided by Hetch Hetchy Reservoir could be accomplished by investing in new surface or groundwater storage, similar to the projects shown below. Together, Los Vaqueros, Eastside and San Vicente Reservoirs, along with a variety of groundwater projects, comprise more than 3,000,000 acre-feet or 8 times the volume of Hetch Hetchy Reservoir.  


Semitropic, in Kern County adjacent to the California Aqueduct, banks groundwater for most of California's largest cities.



Los Vaqueros Reservoir in Contra Costa County, built in 1998 and later expanded to hold 160,000 acre-feet of water, may be expanded further. 










Instead of relying on new storage, the water supply function of Hetch Hetchy Reservoir could be replaced with development additional annual supply through water recycling or transfers. Typically, water system planners use historic drought periods to assess system performance. The historic (modern) drought in the Tuolumne watershed lasted 6 years, from 1987-1992. Therefore, developing 60,000 acre-feet of new supply annually would replace Hetch Hetchy Reservoir's 360,000 acre-feet of water storage.

Recently developed recycling facilities and water transfer activity, mostly based in southern California, provides more than 649,000 acre-feet of water per year - enough to replace Hetch Hetchy Reservoir 11 times over. 


When irrigation districts sell some of their water, the revenue can be used to fund irrigation improvements or groundwater recharge projects, resulting in improved agricultural production.



Water recycling plants employ the same filter technology as desalination plants, but require far less energy to operate and generally do not threaten marine ecosystems.

A summary of selected water supply investments developed by California water agencies in recent years is provided below in Table 1. For more detail on these projects, see Restoration of Hetch Hetchy Valley and San Francisco's Water Supply, Restore Hetch Hetchy, 2014.


Table 1: These selected water supply investments developed over the past 25 years by other California water agencies would replace Hetch Hetchy more than 19 times over. Restore Hetch Hetchy stands ready to work with San Francisco on any or all of these alternatives.

Additional analyses and discussion of these and other alternatives are provided in the following reports.