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Sonoma's Urban Water Management Plan, a document required by state law to encourage realistic planning, finally won city council approval April 16, after a slate of revisions were performed by the consultant preparing the plan.

Brown & Caldwell, a Walnut Creek consulting firm, had presented a plan in August 2007 that projected a secure water supply for Sonoma through the year 2030. But that plan made several assumptions that members of the city council were not willing to accept as reliable fact. The new projections dramatically changed the city's supply scenario and forecast a hypothetical shortfall within two years. That doesn't mean Sonoma will soon run out of water, because the projections have a substantial built-in cushion. But it does mean that city planners will probably take a more cautious approach to future supply projections.

The vast majority of Sonoma's water comes from the Russian River via a pipeline owned by the Sonoma County Water Agency. Sonoma is under contract to receive up to 3,000 acre feet a year (an acre foot equals about 326,000 gallons) with a daily peak flow of 6.3 million gallons. But delivery of the contracted amounts could be impacted by any of three uncertainties that cloud future water supplies. They include the unproven assumption that state regulators will allow the water agency to increase Russian River diversions by 25 percent as planned; that water currently stored behind Warm Springs Dam can be released into the Russian River fast enough to satisfy demand; and that the currently inadequate pipeline delivering Russian River water to the Sonoma Valley will be upgraded quickly enough to keep pace with demand. The increase in Russian River diversions has long been assumed as a given provided the county demonstrates adequate levels of water conservation. But uncertainties associated with climate change, and future flow regimes required for the preservation of endangered salmon stocks, make river flow patterns harder to predict.

Warm Springs Dam impounds ample quantities of water, but release of impounded flows from Lake Sonoma are limited by channel restrictions necessary to protect juvenile steelhead, another endangered or threatened fish species under federal protection.

And completion dates for a new parallel pipeline to deliver more water to the Sonoma Valley keep being pushed farther back. An additional assumption behind the originally rosy forecast that Sonoma would receive adequate  water for the next 22 years, was that during dry summer months when river water is lowest, the city could increase its well output to as much as 404 acre feet per year.

Historically, all of Sonoma's water came from wells, and peak production prior to 1964 was about 656 acre feet. But that year the city switched to Russian River water and since then the Valley's population and wine production, which relies heavily on groundwater, have grown  significantly. The most water delivered from municipal wells in recent years is the 84 acre feet pumped in 2002. There is as yet no accurate estimate of the amount of reliable groundwater available, so assumptions about peak production are mere guesses.

The original Brown & Caldwell plan also predicted the city would be able to utilize 50 acre feet of reclaimed wastewater from the Schellville treatment plant, but there is no pipeline and pumping system in place to move the water to where it could be used.

Stripping out these assumptions from the supply scenario, Brown & Caldwell vice president Paul Sesky told the council that the new figures showed Sonoma water demand exceeding supply by as much as 543 acre feet by the year 2010. After that, conservation would be expected to increase and the shortfall would drop to about  477 acre feet a year.

Sesky described the future deficits as "not that substantial," arguing "you can increase groundwater use in the short term, probably safely ... But year-after-year, that's another question."

City Planning Director David Goodison added that  "the probability of being able to use groundwater supplies, it's very high."

But Planning Commissioner Michael George warned against "mining groundwater" and suggested weather patterns will change. "There's a high probability," he said, "it's going to be much, much drier."

Mayor Joanne Sanders pointed out the plan "is not a solution," and both she and Councilmember Ken Brown raised the specter of a possible future building moratorium as a topic worth addressing.

With no supply guarantees and a sense of caution, the Council then approved the Urban Water Management Plan on a 5-0 vote.

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