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NW Fishletter #393, May 6, 2019
 Flexible Spill: No Surcharge, But Plenty Of Discussion
A week after flexible spill operations began on four Columbia River dams, the Bonneville Power Administration held a workshop to explain how it plans to avoid passing the spill costs on to ratepayers, while hydroelectric dam operators discussed the quirks of a spill program that's never been tried before.
Under an agreement involving BPA, the U.S. Army Corps of Engineers, the Bureau of Reclamation, the states of Oregon and Washington, and the Nez Perce Tribe, eight federal dams on the Snake and Columbia rivers are now spilling water at 120 percent total dissolved gas (TDG) levels for 16 hours each day to aid downstream juvenile fish migration, and reducing spill for eight hours each day to help BPA when power costs are higher. Those operations will continue through mid-June, when summer spill begins.
Dam operators already knew that increasing TDG levels at one dam influences dissolved gas levels at the next dam downstream. But after a week of attempting to keep gas levels at all four Columbia River dams at--and not above or below--120 percent for 16 hours a day, Dan Turner, the Corps' Northwest Division water quality team lead for the Columbia River, was already calling The Dalles his "problem child."
"We had an interesting first week," Turner told members of the Columbia River Technical Management Team (TMT) on April 17--a full week after flexible spill began April 10 at McNary, John Day, The Dalles and Bonneville dams.
Operators started off the spring spill season with flows that were too high for flexible spill hours to apply. Operating at maximum generation, TDG levels were already at--and in some cases above--120 percent. At Bonneville Dam, total flow peaked at 392.4 kcfs on the night of April 10 before flows began to recede.
With reduced flows, operators began to adjust spill levels to 120 percent TDG. At The Dalles, the spill adjustments ranged from 140 to 153 kcfs, which resulted in differing and inconsistent TDG levels, Turner said.
He explained that part of the difficulty at The Dalles stems from a TDG gauge that is located almost three miles downstream from the dam, which leaves a two-hour lag in information. So when operators make a change to influence the TDG, they don't know the impact for a couple of hours. In addition, increasing TDG at John Day Dam upstream has a significant influence on TDG levels at The Dalles, sometimes pushing it above the 120-percent limit.
According to data posted on the TMT website, TDG levels at The Dalles exceeded the daily criteria from April 13 through April 17, rising each day to 123 or 124 percent for more than six hours. Detailed information on spill and TDG levels is available on the TMT homepage.
Asking for input from the team, Turner noted that by keeping TDG at 120 percent in John Day's tailwater, operators at The Dalles might have to cut spill significantly--potentially to zero--to keep tailwater at The Dalles below 120 percent TDG. He suggested a more balanced approach would be to lower TDG at John Day to enable continuing spill at The Dalles.
Paul Wagner, TMT member representing NOAA Fisheries, suggested spilling 40 percent of the flow at The Dalles, and allowing a lower spill at John Day.
Operators planned to continue discussing the spill levels with salmon managers, and will revisit the issue at the next TMT meeting on April 24.
Turner also reported that the four Snake River dams--Lower Granite, Little Goose, Lower Monumental and Ice Harbor--where flexible spill has been in operation since April 3--are operating well after initial adjustments. "Yesterday, we got 120 percent for the four projects; we didn't change anything," he said, adding that dam operators continue to make very small changes to maintain the 120 percent TDG levels.
BPA, in an email to NW Fishletter, said from its perspective, implementing the flexible spill operation has gone well so far. "We have been able to implement flex spill in the fashion we anticipated in our planning activities. While there are always unique conditions and operational realities that do not appear in a modeled scenario, our initial impression is that the overall spill operation and the flex spill component are behaving as expected," the agency's statement said.
Bonneville is also proposing to forego any spill surcharges to customers this year, and instead plans to charge the Fish and Wildlife Program $34 million for the additional costs from spilling water over the eight dams. Last year, customers were charged an additional $10.2 million for the costs of spring spill, and the Fish and Wildlife Program was charged $20 million.
On April 18, Bonneville hosted a workshop to explain preliminary plans for its 2019 spill surcharge. Daniel Fisher, BPA's power rates manager, explained that when 2018 and 2019 rates were set, Bonneville was facing a spring spill injunction but was not sure what the consequences would be. The spill surcharge tries to mimic what rates would have been if BPA had known what the spill was going to be, he said.
In 2018, the surcharge was based on the court-ordered requirement to spill to gas caps, for a total cost of $38.6 million. This year, the surcharge is based on the flexible spill operation, for a total cost of $34.9 million. Those are not actual costs, but are based on the average amount of lost generation under those spill scenarios over 80 historical water years, multiplied by the rate case forecast for the price of electricity at Mid-Columbia projects.
Adjustments that reduced the surcharge to zero this year include a cost reduction permitted at the BPA Administrator's discretion, which is proposed at $34 million charged to the Fish and Wildlife Program. The surcharge amount also reflects a credit that will not be received due to Fish and Wildlife Program reductions, a formula adjustment to account for the portion of electricity going to non-Slice customers, and the impact that more spill has on market prices for remaining power sales.
BPA operations research analyst Milli Chennel said the new flexible spill criteria will result in a 223-aMW decrease in generation, which is "a little less of a decrease than we saw in fiscal year 2018," which resulted in a 253-aMW decrease. Both figures are based on the average hydropower generation from 80 historical water years.
She noted that there were no changes in summer spill last year, although the flexible spill agreement could also affect spill this summer, and is reflected in this year's costs.
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