Diversion factor

PHIL NELSON THE TRINITY JOURNAL A boat ramp at Trinity Center falls far short of a lowered Trinity Lake.

Preliminary figures from the Trinity River Restoration Program indicate that 456,641 acre-feet of water was released from Lewiston Dam to the Trinity River during the 2009 water year which ended in September, while 539,172 acre-feet was diverted via underground tunnel to Whiskeytown Lake and the Sacramento River.

It was a dry year, and inflow to Trinity Lake was approximately 800,000 acre-feet, so the lake was drawn down substantially.

The split weighted toward diversion goes against former Interior Secretary Bruce Babbitt's Trinity River Record of Decision which calls for the river to get the greater proportion of water during a dry year, said Tom Stokely, retired Trinity County senior resource planner and a board member of the California Water Impact Network.

In a dry year, the Record of Decision calls for a minimum Trinity River allocation of 452,600 acre-feet and an average Central Valley diversion of 358,400 acre-feet.

The Trinity River flows toward the north end of Trinity Lake between Trinity Center and Coffee Creek. The lake was drawn down significantly this past year, with nearly 1 million acrefeet released .

The Trinity River Restoration Program's executive director, Mike Hamman, disagrees.

Hamman is a federal Bureau of Reclamation employee, but the program he heads serves many agencies involved with river restoration. He said the Record of Decision sets firm volumes for water down the river depending on water-year type — and that volume was met — but the amount diverted for agriculture can be tweaked for operational purposes.

"The Central Valley office makes that call," he said. "There aren't any hard and fast rules except for the fishery flow."

Furthermore, although it sounds counterintuitive, Hamman said the additional water was sent through the tunnels in order to aid Trinity River fish.

He explained that a large block of water was diverted due to what is essentially a temperature and plumbing issue: During summer, release to the Trinity River is to be 450 cubic feet per second. With the lake low, in the heat of summer CVP managers must send approximately three times that volume through Lewiston Lake to keep the water cool enough for fish on the other end. Sometimes even that doesn't do the trick and they use Trinity Lake's lower, auxiliary outlet to get the lower, cold water. However, the lower outlet was not originally intended for temperature control and was built to be fully open releasing about 1,800 cfs or fully closed. Otherwise, valve damage could result.

Operators have also tried pulsed flows through the lower outlet as one way to use it without releasing as much water, Hamman said.

In another issue, water through the lower outlet does not go through the power plant at Trinity Dam, which affects power users, including the Trinity Public Utilities District.

Bureau of Reclamation Area Manager Brian Person noted that over time, the water split has been what was called for in the Record of Decision — a 53 percent diversion and 47 percent down the river.

He noted that in an extremely wet year much more water is available for diversion, but "would that happen that year? Probably not because you might want to store some of that."

From the California Water Impact Network, Stokely does not think enough water has been stored in good water years in Trinity Lake.

Keeping the lake higher would mean more cool water available for fish without sending such large amounts through the system that some must be diverted, he said.

"It's pretty obvious if the reservoir gets too low there won't be cold water available to keep spawning fish and incubating eggs in the gravel alive," he said.

"It's a very unfortunate plumbing circumstance that they have to send three times more water down the hill to keep the Trinity cold," Stokely added. "They need to have a physical solution to that and they also shouldn't send so much over the hill in the wetter years."

In addition to storing more in the lake during wet years, Stokely suggested other solutions could be to put a pipeline around Lewiston Lake to deliver cold water to the river or tear down Lewiston Dam and pump water into the diversion tunnel, providing seven more miles of fish habitat.

From the restoration program, Hamman said it is too early to determine what kind of water year this will be, although the National Weather Service prediction for the next few months is for a 70 percent chance of normal or above normal precipitation.

If it is another dry year, he said, "we will be challenged as far as the temperatures go."