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Pulse flows scheduled for Mokelumne River

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Posted: Sunday, September 27, 2009 10:00 pm

In an effort to kickstart a slumping salmon population, East Bay Municipal Utility District is pumping extra water from Camanche Reservoir into the Mokelumne River next month.

The influx of water, called pulse flows, will help on several fronts, said Jose Setka, supervising fisheries and wildlife biologist at EBMUD. One way is to attract Chinook salmon, whose numbers in the Mokelumne River have been dwindling.

"Releasing or altering the flow can queue fish to come up river," he said, adding that rivers generally don't run at the same flow and consistency levels.

He said that wildlife, particularly salmon, take their queues from water levels and will return to the Mokelumne.

"They sense something is happening and gotta get out," he said.

Ideally, Setka said, the salmon are staging in the Delta or inner bay, and the pulse flows will encourage them to move.

He said there are positive signs for a stronger salmon run this year.

"We saw our first fish go by Woodbridge today," he said. "Last year, that didn't happen until after Nov. 1."

The pulse flows will also help remove sediment, debris and vegetation in salmon spawning grounds. That will help by giving salmon a place to lay their eggs and reproduce.

The extra surge of water is the only way to redistribute rocks and gravel on the riverbed. Setka said the velocity generated from 2,000 cubic feet of water per second would be sufficient to stir up the gravel at the bottom of the river.

"Pulse flows are desirable," said Bill Jennings, executive director of the California Sportfishing Protection Alliance. "It's still not enough to restore the river."

Jennings said the salmon run has been down in the past several years, but that the situation is starting to improve.

"When you provide lots of good quality water, you get good fish," he said.

The pulse flow will use a total of 18,000 acre-feet of water. That is enough water to cover 18,000 acres in one foot of standing water.

There has not been a significant pulse flow in the Mokelumne River since 2006 because drought conditions made water scarce and a pulse flow impossible.

The Chinook salmon population has drastically dwindled in that time.

In 2005, there were roughly 16,000 salmon in the Mokelumne River. Now there are only several hundred. Setka said a healthy average for the Mokelumne River is 4,000 adult Chinook salmon during most years.

Salmon numbers in the river are low for several reasons. The Mokelumne River discharges first into the Delta, and there is no bypass for the fish. The fish are subjected to crosscurrents and being sucked into pumps that regulate the flow of the Delta.

It's a problem for young fish making their way to the ocean because they are not strong enough to fight the currents and avoid getting sucked into the water pumps and killed. The Mokelumne River feeds into the central Delta, and regularly has problems with fish survival.

Setka said he is cautiously optimistic about the success of the pulse flow, and said the results will be ready shortly after the process is finished.

"We will know by the beginning of November if we are going to have a good run," Setka said.

Setka said there are video monitors on the fish ladders at Woodbridge Dam and they can monitor the activity of the salmon in real time.

The pulse flows are scheduled to run through Oct. 17. The biggest pulses will take place from Oct. 6-10 and will occur at 8 a.m. and 2 p.m. on those days.

The water level at Lodi Lake will rise slightly and the Mokelumne River level will go up as well due to the pulses. Setka said the upper part of the Mokelumne River should rise between two and five feet.

Setka said the pulses are possible even in the midst of a three-year drought because Camanche Reservoir benefited from some wet weather in May that built up reserves. Camanche Reservoir is supplied by snow pack, and Setka said a late-season storm helped fill it.

"We lucked out," he said.

Others are pitching in to help ensure the pulse flow is as successful as possible.

"We are trying to work with other district water agencies to close cross channels and prevent water from going into the Sacramento River," said Michael Healey, lead scientist for the California Bay-Delta Authority.

Healey said the Bureau of Reclamation and the National Marine FIsheries Service are the agencies he wants to work with to close cross channels and maximize the effectiveness of the pulse flow. Healey said he would know by next week if he would have the participation of those groups.

The pulse flow will still be good for the Mokelumne River and the salmon even if the cross channels are left open, but a direct flow into the river would be especially beneficial, Healey said.

"We need to get Mokelumne fish to the Mokelumne River," he said.

Contact Jordan Guinn at jordang@lodinews.com.

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