Mother Nature is a tough act to follow with the motors and steel gates of a dam and only half the water, but scientists with the Trinity River Restoration Program would like to try to get the river closer to its natural rhythms.
The program is investigating whether to radically change the way water is released from Lewiston Dam to the Trinity River in order to provide better conditions for fish.
Currently, a flow schedule is decided upon in April based on the water year forecast, with a peak flow released in spring to mimic snowmelt. But the river is kept under wraps through the winter, even though without Trinity and Lewiston dams it would surge during storms. Program scientists are looking at bringing that back within certain limits.
Instead of coming out with a fixed schedule for river releases, they’re studying the possibility of adjusting releases frequently based on estimated inflow to the Trinity Reservoir. Synchronizing with the flows in tributaries, the timing of the river releases would change but the overall amount released to the river annually would not. On average, 47 percent of inflow is released to the river with the remainder available for Central Valley Project uses, and that wouldn’t change.
Trinity County Sup. Keith Groves, a member of the Trinity Management Council which guides the restoration program, shared why this timing revamp is being considered.
“I think there is a realization that though we feel we’re doing good work in the river, we’re making the river a more dynamic river, it is not translating to more fish,” he said.
From the restoration program, Executive Director Mike Dixon said, “At the staff level across the various agencies the writing’s been on the wall a long time. That’s the direction we’re ultimately trying to go.”
Dixon speculated that if approved the switch to synchronized flows couldn’t be made until 2023 at the earliest. But for now, the program has the TMC’s approval to move forward with studies.
“I think it’s pretty exciting,” Dixon said.
He noted that anadromous fish evolved under frequently changing water conditions driven by many different influences. Storms raise rivers and creeks quickly and then they subside. Spring snowmelt is variable as the weather warms and cools. Trees and other vegetation also cause fluctuating water levels.
The rising and receding river dislodges bugs, adding fish food in the water. Storm flows on the Trinity should help to disperse sediments sent into the river by tributaries during storms, Dixon said.
He noted that the Carr fire burned the Deadwood Creek watershed, which now puts large amounts of sediment into gravel beds on the river during storms. “Each time you got a big plume of sediment coming into the river you get a big deposit and no big flow to move it,” he said.
“There’s pretty good information from other rivers and the Trinity that the ecology of healthy rivers is driven by these disruptive (storm) events,” Dixon said. “That’s what these fish evolved with.”
The synchronized flows would also move the spring peak flow on the river forward. Dixon said there is good science indicating that pushing the bulk of the water forward will cause better conditions for juvenile salmon later in the year.
Although releases at Lewiston Dam would be based on a percentage of estimated inflow at Trinity Reservoir, there would be upper and lower limits. Historically in a very dry year the flow at Lewiston could have been as low as 100 cubic feet per second. At that rate the temperature targets would be exceeded. On the other side of the scale, due to infrastructure the release can’t exceed 11,000 cfs.
The idea of basing river releases on inflow to Trinity Reservoir isn’t a new one. In fact, it was one of the alternatives considered prior to the Trinity River Record of Decision in 2000. The difference is in 1999 the daily average inflow over a week was used to determine the releases. Storms are fleeting events, and taking an average meant that peak flows high enough to move sediments, scour riparian vegetation and reshape the river channel wouldn’t occur often enough.
Moving to synchronized flows is no small change. Study and consultation with other agencies are needed. Although there is room in the Record of Decision for timing changes based on science, Dixon said environmental studies will be needed analyzing not only the benefits but any detriments.
The studies would tier to the existing NEPA documents without throwing out the Record of Decision, he said. “We don’t want to jeopardize the water that people fought so long so hard to get.”
One major barrier could be the infrastructure at Lewiston Dam.
The motors that operate the Lewiston gates weren’t designed for frequent, small changes, Dixon noted. “It burns them out.”
In fact, there have already been issues with the gates that prevent the program from implementing multiple small flow fluctuations. These diurnal fluctuations were halted by the federal Bureau of Reclamation after an electric motor associated with a radial gate at Lewiston Dam failed last May. To minimize risk to the remaining gate, restoration flows were suspended until repairs were completed.
In response to a written request from TMC Chair Justin Ly that the diurnal flow variability be reimplemented or Reclamation provide justification as to why not, Reclamation Mid-Pacific Region Director Ernest Conant responded in writing regarding the “aging infrastructure” at Trinity Powerplant, Trinity Dam and Lewiston Dam completed 55 years ago.
“Until Reclamation receives approximately $5 million in appropriated funding to change the entire operating system of the Lewiston radial gates to be more conducive to the minor flow adjustments that are being requested by the TMC, Reclamation will not be able to implement the diurnal flow variability you are requesting,” Director Conant wrote.
As to whether the gates would be a barrier to synchronized flows, Dixon said, “there will have to be a two-way conversation on what Reclamation can actually accommodate versus what the scientists are recommending.”
At its meeting last week in Redding, the TMC authorized additional projects needed to answer questions regarding synchronization of flows using money saved from vacant positions.
The motion passed 7-1, with the Hoopa Valley Tribe opposed.
The TMC also voted that a letter be written to Reclamation asking that the agency find the $5 million to fix the issue with the Lewiston gates.
Sup. Groves said he’s seeing very strong support from the scientists in the program for the synchronized flows. Previously, the restoration staff had been told it couldn’t be done with the existing environmental documents.
“We’ve (the TMC) told them to be more out of the box,” Groves said. “This opens some things so they can be more creative in their thinking.”