California's State Water Resources Control Board appears to be moving forward with its proposal to restore healthy flows to the lower Stanislaus, Tuolumne and Merced Rivers - some of the State's most dewatered streams. Specifically the State Board proposes to require that these rivers retain at least 40% of their natural flow from February through June. The proposal would more than double the flow in some dry years. 

San Francisco and its Bay Area customers may be hit the hardest by the flow increase. We do have sympathy for the City as it faces this prospective challenge. This sympathy is limited, however, as successive generations of water system management have failed to diversify in spite of its tenuous junior rights to Tuolumne River flows. 

The Los Angeles Times has sided with the rivers, opining that its time for San Francisco to "leave some water in place for the good of the state, each other, and ourselves."

When San Francisco chose to pursue the Tuolumne River as its principal water source a century ago, senior water rights already belonged to Turlock and Modesto - the oldest irrigation districts in California. San Francisco would get only those supplies in excess of the districts' needs.

San Francisco's share of the Tuolumne's flow has been more than sufficient in most years, but is minimal in dry years and especially problematic in extended droughts. As a result, the City has invested in oodles of surface storage in the Tuolumne watershed. Hetch Hetchy Reservoir is San Francisco's best known facility but accounts for only about 25% of its storage in the watershed, with Cherry and Eleanor Reservoirs, and the City's water bank in Don Pedro Reservoir accounting for the rest.

When the Turlock and Modesto Irrigation Districts built Don Pedro Reservoir (at 2,030,000 acre-feet, one of the largest in California), San Francisco paid half the cost. In exchange, the City received a water bank that could hold 570,000 acre-feet year round and up to 740,000 acre-feet once floods were no longer a threat. The Districts were initially responsible for meeting all instream flow requirements downstream of Don Pedro, but San Francisco agreed to be responsible for supplying more than half of any future increase ( 51.7121% to be precise - see page 11 of the 1966 "Fourth Agreement" between San Francisco and the Districts.)

So even though the Districts use 4 times as much Tuolumne River water, San Francisco is expected to be responsible for meeting most of the State Board's increase. The proposed rules will matter little in wet years, but will have significant effects in dry years and especially in droughts. 

Figure 1 shows actual flows on the lower Tuolumne River in a wet, average and dry year, as well as how much water San Francisco and the Irrigation Districts diverted in those years. The blue bars show how much additional flow would be required in the average and dry year. To meet the requirement, San Francisco and the Irrigation Districts would either need to reduce their diversions or draw down reservoir storage. Note that in 1991, San Francisco's obligation to the lower river (51.7121% of the blue bar) would be greater than its diversion to the Bay Area.

How did San Francisco end up in this tough situation? There are several contributing factors. The City fought tooth and nail a century ago to build Hetch Hetchy Reservoir in Yosemite National Park with full knowledge that its rights on the Tuolumne River were junior to the Irrigation Districts. And when it decided to participate in the Don Pedro Project, it agreed to meet more than half of any future required flow increase - no doubt not expecting public sentiment and the State Board to support a significant increase.

Finally, San Francisco has failed to substantially diversify its water supply portfolio as urban agencies throughout California have done over the past 25 years. As Table 1 below shows, other agencies have built reservoirs close to their customers, banked groundwater in their service areas and in the Central Valley, recycled water and developed long term relationships to buy water from agricultural users in dry years. San Francisco has done comparatively little. (Diversification makes sense for a number of reasons. Properly done, diversification would also increase resiliency to global warming, earthquake, fire or other potential catastrophes.)

So it's easy to have sympathy for the hardworking and dedicated SFPUC staff whose planning must assure reliable supplies are available during the next drought, and may need to do so with a diminished supply from the Tuolumne River. Viewed over the course of the last 100 years, however, San Francisco has failed to understand the jeopardy inherent in relying so heavily on a single source where its rights are junior.

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One last note: Restore Hetch Hetchy remains committed to retaining San Francisco's Tuolumne River supply when Hetch Hetchy Reservoir is emptied and the valley restored. The additional improvements to San Francisco's water system, necessary to accommodate restoration of the valley, are likely to change slightly but not substantially as a result of a final decision by the State Board.