Tackling one of the American West's most contentious issues, a new government report assesses the demands on Sonoma County's largest underground water source against a future that includes population growth, agricultural needs and the wild card of climate change.
The report by the U.S. Geological Survey provides a detailed profile of the groundwater beneath the 261-square-mile Santa Rosa Plain watershed, home to about half the county's population, including the cities of Santa Rosa, Windsor, Sebastopol, Cotati and Rohnert Park.
About 12,000 wells operated by the five cities, the county water agency and private homes and ranches on the Santa Rosa Plain pump about 53,000 acre-feet of water per year from the ground, matching the amount of water the agency draws from the Russian River.
"We are planning for an uncertain future," said Marcus Trotta, a Sonoma County Water Agency hydrogeologist.
The 199-page report, packed with hydrologic and geochemical data, is the first study of the underground watershed in 30 years and part of the cornerstone for an ambitious effort to establish a groundwater management plan for the Santa Rosa Plain.
A 30-member Basin Advisory Panel representing cities, water customers, agriculture, industry and environmentalists intends to develop, by late this year or early 2014, a plan to "manage, protect and sustain groundwater resources" in the plain.
It's a chore that will require balancing competing interests, such as urban growth versus agricultural demand, and accounting for a future fraught with more volatile weather — droughts alternating with floods — brought on by climate change.
"Future growth in population and demand for water coupled with a changing climate ... are likely to increase stresses on the region's groundwater resources," said a groundwater primer prepared by the Water Agency.
"We have to maintain it," Sonoma County Supervisor Shirlee Zane said, noting that "we can't build new houses or have new farms without water."
To come to an accord over water, Zane said, will require a third leg to the bromide long attributed to Mark Twain: "Whiskey is for drinking; water is for fighting over."
"Water is for sharing," Zane said. "It's life."
Lex McCorvey, executive director of the Sonoma County Farm Bureau, which has a representative on the advisory panel, said he agrees with that concept in principle.
"We're going to need to learn how to share water and prioritize our use," McCorvey said, acknowledging that a tug-of-war between urban and agricultural interests "certainly is a possibility."
But McCorvey said he will withhold judgment on the groundwater management plan until the details take shape.
Agriculture, an $821 million local industry, is vital to the county's economy, he said, adding that farms "need their fair share of water."
Kathy Hayes, executive officer of the North Bay Association of Realtors, which also has a seat on the advisory panel, said she is looking forward to the USGS report, which will be presented at a public workshop at 6 p.m. today at the Finley Community Center, 2060 West College Ave., Santa Rosa.
"We're not going to presuppose where this process ends up," Hayes said, referring to the management plan.
Jane Nielson, an advisory panel member representing the Sonoma County Water Coalition, said the report documents how a change in water policy can positively affect groundwater supply.
Heavy pumping from municipal wells in the Rohnert Park-Cotati area in the 1980s and '90s had lowered the underground water table by as much as 100 feet, Trotta said.