Creating shelter for coho and steelhead in Dry Creek with boulders, logs and side channels will offer enough protection to meet federal regulations for those endangered and threatened species, according to a $2 million study released today<NO1>Wednesday<NO>.

The creek work could cost $36 million to $48 million on six miles of the 14-mile waterway that serves as the conduit carrying water from Lake Sonoma to the Russian River, from where some of it is diverted to Sonoma County Water Agency customers.

If those measures don't work, however, a last resort could be a $141 million pipeline on Dry Creek Road from Warm Springs Dam to Healdsburg, where it would empty into the river.

"I have confidence we won't have to build the pipeline. I think we will be able to build the six miles in Dry Creek and meet the federal guidelines," said Erik Brown, the water agency's project engineer.

The challenge is how to deliver enough water down Dry Creek to serve the water agency's 600,000 customers, but slow the stream enough to provide favorable fish habitat, said Dave Manning, water agency principal environmental specialist.

"It flows too swiftly and it doesn't contain enough elements that juvenile coho and steelhead find conducive," Manning said.

Coho and steelhead thrive in cold, slow-moving water where they can spend one to two years before migrating to the ocean.

Coho, which are listed as endangered, came close to extinction in the Russian River system with as few as 20 counted a few years ago, Manning said. However, a breeding program by state Fish and Game at Warm Springs' Don Clausen Hatchery that started in 2001 is credited with helping build the count to an estimated 200 to 300 this year in the river and its tributaries.

The National Marine Fisheries Service three years ago ordered the water agency to improve conditions in the Russian River, Dry Creek and tributaries. The measures include in-stream work to enhance habitat on Dry Creek, a reduction in summer flow in the Russian River and creation of a fresh-water lagoon at the mouth of the Russian River at Jenner.

The first of the work in Dry Creek is being designed and will be under way in the summer of 2012 on a one-mile stretch at Lambert Bridge, It will cost of $7 million to $8 million.

"It's a mix of projects," Brown said. "There will be backwater side channels, alcove-type projects, basically provide low-velocity water and pool habitat, specifically for coho to hang out in in; they prefer slow-moving habitat."

The remainder of the work will occur over the next several years, Brown said. By 2018, the success of the Dry Creek habitat work will be assessed and a decision made on whether a pipeline is necessary.

The preferred pipeline route would follow Dry Creek Road and rely on gravity to move the water from an inlet near the dam to the Russian River, replacing Dry Creek as the conduit to water agency customers.

The draft studies were conducted by Inter-Fluve Inc. of Hood River, Oregon; Sanders and Associates Geostructural Engineering Inc. of Granite Bay; and HDR of Folsom. The feasibility studies and the work in Dry Creek are being paid for by a special Sonoma County property tax levied for construction of Warm Springs Dam and by the Army Corps of Engineers.