Sonoma County grape growers aiming to convert forested hillsides with neat rows of vineyards will have to prove their projects won't damage local waterways under draft regulations released Thursday.

The new rules, proposed by Sonoma County Agricultural Commissioner Tony Linegar, would prohibit tree removal on the steepest of slopes, keep vineyards 50 to 100 feet away from unstable hillsides, and require three years of follow-up to ensure the regulations are effective.

"The ultimate goal of these standards is to protect water quality," Linegar said.

The new restrictions would fundamentally alter the way the wine industry farms on hillsides, increase the costs of vineyard development and hurt small farmers the hardest, said Nick Frey, president of the Sonoma County Winegrape Commission.

"We run the risk that we're essentially going to price a lot of small guys out of the market," said Frey. Forty percent of Sonoma County's nearly 60,000 acres of grapes are grown in vineyards of 20 acres or less, he said.

The proposals reflect a growing unease over vineyard projects that encroach on undeveloped hillsides as growers seek to capitalize on Sonoma County's reputation as a world-class grape growing region. Over the past several decades most of the easily developed agricultural land suitable for grapes has been converted to vineyards.

Hillside vineyard planting has been halted since January when the Sonoma County Board of Supervisors issued a four-month moratorium to allow time to craft new rules.

County officials were concerned that several pending vineyard projects would require removing large numbers of trees, something existing regulations do not restrict.

Two Annapolis-area proposals call for the conversion of more than 1,900 acres of forest into land for wine grapes. Those two projects — the 146-acre Artesa Vineyard proposal and the 1,769-acre Preservation Ranch project — would be subject to the updated regulations, Linegar said.

The county allows the development of hillside vineyards on slopes up to 50 percent under an erosion control ordinance passed in 2000. But the ordinance, known as Vineyard Erosion and Sediment Control Ordinance, or VESCO, contains no restrictions specific to tree removal, something Linegar has called an "oversight."

Tree roots help with slope stability, and tree canopies help slow surface runoff, he said. Under current rules, a vineyard or orchard project is "Level 2" if the slopes involved are over 15 percent grade for normal soils or 10 percent for highly erodible soils.

A project will be subject to the new regulation if it is Level 2 and calls for removing more than half an acre of trees. Under the new rules, when soils are unstable, or are "cohesionless," tree removal will not be allowed on grades above 40 percent. For those between 25 and 40 percent, a "slope stability analysis" will have to be performed by a licensed geologist to ensure it is safe to remove trees.

It should be "common sense" that people shouldn't be removing trees from steep unstable slopes, Linegar said. "We want to prohibit removing trees from active landslides," he said.

In addition, vineyards will need to be set back 50 feet below a grade of 50 percent or more and 100 feet above such a grade.

Hilltop vineyards also will face additional scrutiny. On flat hilltops with unstable soil, the vineyard project will face the same scrutiny as Level 2 projects.

Finally, draft guidelines propose requiring developers of hillside vineyard that involve tree removal to demonstrate the projects would not result in additional erosion or sedimentation of waterways.

To ensure that pans out, three years of follow-up would be required with both photographs of the site and visits from county inspectors. The proposal also suggests the county hire registered civil engineers and certified engineering geologists to review hillside vineyard applications.

The proposed changes were prepared with the help of engineering firm Laco Associates. The county has paid the Eureka-based firm about $24,000 so far for its work, Linegar said.

He estimated the additional cost of complying with the regulations to be from $1,500 for a small-acreage grower to $15,000 for a larger project. Those figures reflect the estimated costs of hiring consultants, Linegar said.

But Frey says the true costs will be far higher, particularly because growers will have come up with "engineered solutions" to comply with erosion-control requirements. That could require entirely different planting techniques, such as diverting water into ditches and holding ponds that increase costs and reduce planting area, he said.

Frey said it's too soon to know what the financial impact to the industry might be. But he said he knows the current moratorium isn't good for business.

"We have jobs and we have economic activity that are sitting on the sidelines waiting for the go-ahead to plant," Frey said.

Forestville environmental attorney Kimberly Burr doesn't think the regulations go far enough. She served on one of the working groups and wishes the proposal addressed more than erosion. She's also not swayed by the claims of over-regulation, asserting that many vineyard projects skirt a true assessment of their impacts.

"You can't expect the public to bear the cost of your business enterprise," she said.

The county has been working to develop the new rules on a tight timeline required the supervisors, who want to review them by April 24.

The draft regulations were released in advance of a an April 11 public meeting in Kenwood to discuss the proposed changes. The meeting is from 7 p.m. at 9 p.m. at the Kenwood Fire Station, 9045 Sonoma Highway.

It will be the first public hearing on the regulations. A prior meeting in Windsor in February wasn't widely publicized, and meetings since have been with groups representing the wine industry or the environmental community.

"We think we have a really good foundation here," Linegar said.