At Restore Hetch Hetchy, we care about reliable water supplies for all communities, but we pay particular attention to San Francisco. After all, restoration can only be accomplished if water supplies for the San Francisco’s and its wholesale customers are undiminished. Fortunately, this can be accomplished,. As we have said over and over, not a drop need be lost when Hetch Hetchy Reservoir is emptied and the valley is restored. For more information on the solutions we recommend, see our Summer Newsletter or Water and Power System Improvements Necessary to Accommodate Restoration of Hetch Hetchy Valley in Yosemite National Park (2018).
Fortunately, San Francisco’s water system is in good shape. The City’s supplies in its Tuolumne watershed reservoirs are substantial, and are designed to last through a lengthy drought. Water managers cannot be blamed, however, for worrying about extended droughts – that’s their job.
Figure 1 provides a snapshot of San Francisco’s water rights over the last three years, along with its average diversions to the Bay Area and its storage capacity in the Tuolumne Watershed. Water Year 2019 was good to San Francisco, providing more than enough flow to fill Hetch Hetch Hetchy Reservoir, Cherry and Eleanor Reservoirs, and the City’s water bank in Don Pedro Reservoir.
2020 was a dry year and San Francisco’s water rights yielded less than its need to divert water to the Bay Area, so it needed to withdraw about 60,000 acre-feet from its stored supplies (evaporation and losses play a small role in the need for storage withdrawal as well).
2021 has been critically dry and San Francisco’s junior water rights on the Tuolumne River have provided only 44,873 acre-feet of supply (The Turlock and Modesto Irrigation Districts have senior rights and are entitled to more than 10 times as much of the river’s flow in 2021.) So this year, San Francisco will need to draw down its storage by 180,000 acre-feet or so.
Still San Francisco’s system will be in good shape even if the drought persists another year. But for everybody’s sake, we hope water year 2022 (which begins October 2021) will be good and wet. And for the sake of the fires, let’s hope the rain comes early as well.