The Mokelumne River from a bird's eye view. Photo by: Roger Phelps

A pulse will return to an ecologically moribund Mokelumne River this month as water flows are increased sharply by dam releases. The move by the East Bay Municipal Utility District is an attempt to stimulate a spawning run of chinook salmon.

Releases in a maneuver called a "pulse flow" began Monday at EBMUD-operated Camanche Dam. Because 2009 has been less dry than recent years, officials at the water agency have decided to spare some 18,000 acre-feet of water for the struggling chinook, a threatened species, said Charles Hardy, agency spokesman. An acre-foot is 325, 851 gallons.

"We're trying to mimic a big storm," said Jose Setka, agency supervising biologist. "With the recent little storm, this is the best scenario."

Since 2005, when a drought began and EBMUD stopped sparing water for the fishery downstream of its dams, salmon population in the Mokelumne crashed from thousands to just hundreds, according to nonprofit California Sportfishing Protection Alliance.

Flow increases are described as "dramatic," large enough to warrant cautious behavior by people frequenting the river canyon, Hardy said. Varying release amounts will range from 325 cubic feet per second to 2,000 cfs, fluctuating until the end of the flow-increase period on Oct. 19, he said.

"We're changing the flow patterns for a more natural effect," Hardy said.

Federal marine-fisheries officials recently notified EBMUD they were concerned that the agency's Camanche and Pardee dams contributed toward destruction of a salmon fishery.

Unlike dam-keepers on the Stanislaus and American rivers, for example, who are regulated under the California Water Plan, EBMUD has no federally designated earmarks of water for downstream fisheries, and so the Mokelumne has not been contributing its proportionate share to the salmon's threatened habitat, according to Setka.

The decision to increase flows rests both on a calculation that water supply is sufficient and on EBMUD's recognition that "the salmon situation is really bad right now," Hardy said.

He said increased flow also will clean out obstructed nesting areas. Years of low flows have allowed buildups of debris.

"Right now, the (nesting areas) are less attractive, maybe uninhabitable," he said.

Chris Shutes, dam-project supervisor for the sportfishing protection alliance, said of the release plan, "It's a good thing - it should be done on a regular basis, but it's always good when someone takes an interim action like this."

The Mokelumne as a fishery has seen marked ups and downs over the years. Droughts, heavy metal run-offs from an abandoned mine and water mismanagement caused the salmon population to decline in the late 1980s to the point where the dozen or so fish returning were given individual names, according to the alliance.