Mother Nature held back the Columbia/Snake river basin's store of water until mid-May, when an outpouring began that has fish and hydro managers struggling to rein in total dissolved gas created by spill at federal projects.

The quickened snowpack melt has increased river flows and forced involuntary spill across the federal hydro system since May 15, the exceptions being storage projects like Libby and Hungry Horse reservoirs in northwest Montana.

Involuntary spill – volumes above that prescribed for fish passage – is required when water volumes exceed hydro turbine capacity or, in some cases, when all the power that could be generated cannot be sold.

The plunging spill creates TDG, which can at higher levels affect the health of salmon, steelhead and other aquatic life.

Salmon managers this week expressed frustration at decision making last month that kept Dworshak Dam outflows lower than desired for salmon migrations and now are being flushed at such high levels that TDG below the dam has in recent days has surpassed legal limits.

The annual spring melt of Columbia/Snake river basin snowpacks began later than normal but with a gusto. At west-central Idaho's Dworshak Dam, for example, May began with reservoir inflows in the 8,000 to 9,000 cubic foot range. By May 19 they had jumped to 40 kcfs and have since been in the 25 kcfs to 30 kcfs range.

It was decided in early May to begin refill of Dworshak reservoir with outflows reduced from a full powerhouse release of about 10.5 kcfs to 7.5 kcfs on May 8, to 5.5 kcfs a few days later and then to minimum outflow, 1.3 kcfs on May 17.

At the time, federal, state and tribal salmon managers had asked that the higher outflows into the North Fork of the Clearwater River be maintained to supplement flows downstream in the Clearwater and the lower Snake River for the building juvenile salmon migration.

A colder than normal winter and spring kept snowpacks locked up, making it difficult to determine how much water could be released from behind Dworshak early while maintaining certainty that the reservoir can be refilled for fish and recreation.

The reservoir's cold water is used to lower water temperatures in the Snake River for summer fish migrants.

"They (the U.S. Army Corps of Engineers) don't have a year like this in their data base," the NOAA Fisheries Service's Paul Wagner said of the tools used to forecast the "shape" of the runoff. The Corps operates Dworshak and, along with the Bureau of Reclamation, other dams in the Federal Columbia River Power System.

"Volume is nice; shape is everything," said Robyn MacKay of the Bonneville Power Administration, which markets power produced in the FCRPS. Normally, reservoir inflows begin to pick up in late March and, generally, build gradually. This year there was little evidence of increased runoff until May and then a mid-month heat wave followed by higher than normal precipitation triggered the runoff.

"We have more generation than we have a home for," MacKay told members of the multi-agency Technical Management Team Wednesday. The federal, state and tribal hydro and fish managers help guide day-to-day operations of the hydro system.

At Dworshak generation has been increased, though not to capacity, and up to 2 kcfs is being spilled as part of a systemwide effort to get rid of water and, at Dworshak, maintain flood control space for the runoff yet to come.

"Certainly through this weekend overgeneration is going to be a problem," MacKay said of the inability at times to sell all of the power that could be produced. Passing water through turbines creates little TDG.

And even if the power could be sold, "there's more water than turbines," she said. The latest forecast is for at least 5-7 more days of involuntary spill at the four lower Snake River projects.

Russ Kiefer, representing Idaho Department of Fish and Game, said he preferred that more power be generated and less water spilled at Dworshak to avoid TDG exceedances and problems the turbulence is causing anglers. The Nez Perce Tribe's Greg Haller too said the current operation "poses some issues for tribal fishermen."

"We would have preferred more fish friendly operations at Dworshak," Kiefer said. He was critical of the decision last month to scale up refill instead of maintaining higher outflows from Dworshak, which would have created more space for the runoff.

"We were telling you three weeks ago that the flows were going to come," Kiefer said. The Corps' June forecast for runoff into the reservoir is 115 percent of average from April through July, up slightly from the early May forecast.

The Corps' Steve Hall said the agency basically had to hedge its bets in deciding when to begin filling the reservoir so that flood control space is maintained through the spring freshet and fill-up by the end of June is assured. The reservoir reached a low point this year in early May at an elevation of about 1,475 feet, 125 feet below full pool. It has since risen more than 90 feet.

"Because the pool is coming up so rapidly we're watching it very closely," Hall said. The Corps can only fill the reservoir to certain levels based on "snow covered area space requirements." There must be enough space reserved to handle the remaining runoff.

Corps officials said they would do what they could to juggle operations to hold TDG within legal limits.

The spill at Dworshak is part of an overall effort to hold down TDG and "unload megawatts."

"It's to move it around the system," MacKay said. "If we didn't spill there, we'd have to spill (more) somewhere else."

And Dworshak is efficient. Spilling 2 kcfs dodges the same amount of generation as spilling 15 kcfs at high head projects on the lower Columbia.

"It's for gas management," she said. Flows are high, rising from a daily average of about 200 kcfs at Bonneville Dam in early May to an average of 411 kcfs this past week. About 200 kcfs is being spilled there. Flows at the lower Snake's Lower Granite have been over 150 kcfs.

BPA officials say the flows at Bonneville are expected to remain above 400 kcfs into next week.