Black Canyon Estimate Upped 32.5 Percent;
by Bill Rudolph
The improvement will increase generating capacity by 12.5 MW
(Cost estimate now pegged at $53 million)
BPA will pay $53 million towards construction of a third hydroelectric generator at the Bureau of Reclamation's 10.2-MW Black Canyon diversion dam along the Payette River, 30 miles northwest of Boise, Idaho.
That's 32.5 percent more than the $40 million BuRec said it would cost 19 months ago, and doesn't include hundreds of thousands of dollars BuRec will have to pay Idaho for damage to fisheries caused by a botched drawdown that was carried out without public review or notice during the design phase.
Black Canyon is a 183-foot-high concrete gravity dam. Put in service during 1924-25 at 8 MW, its main function is to divert Payette River flow through Black Canon Canal for agricultural use. The reservoir originally had a capacity of 44,700 acre-feet, but heavy siltation over the years has reduced that by over 30 percent, to 31,200 AF.
BuRec said it began drawing down the reservoir on Oct. 8 to an elevation to 2,440 feet to accommodate field work related to the construction. It also planned to use the drawdown as an opportunity to replace sections of the dam's de-icing system, which had been deteriorating. It originally planned to complete the drawdown by late November, but it didn't, and in December, the drawdown was suspended due to heavy rainfall.
BuRec has said a heavy layer of ice formed on the reservoir, and the collapse of an ice dam created a wave of jagged ice that scoured the bottom, sending much more sediment downstream than anticipated.
"The fishery was devastated," said Kevin Lewis, conservation director at Idaho Rivers United. He said BuRec realized during the initial drawdown that there was a rock obstruction that would prevent punching the new penstock into the dam, "so they drew down an extra 12 feet"--well below any operational drawdown in memory--and "not realizing that this would nearly empty the reservoir. By doing this, they released a huge slog of sediment" down the river.
Lewis said IRU is not opposed to adding a turbine, but "clearly things went wrong" in this case. "It's not rocket science to grasp that if you draw down a dam with a lot of sediment, you're going to mobilize the sediment. This should have been predictable. They didn't ask the right people in-house," he said.
BuRec spokesman John Redding acknowledged that the agency "did not anticipate [how] deep and broad" the spread of the sediment would be. But he emphasized it is working with state agencies to mitigate and monitor the damage. He said IDFG is working on a plan to submit for BPA funding.
Rick Ward of IDFG said there was a dramatic spike in turbidity, but that his agency did not understand the extent of the damage until local residents called to complain that the reservoir was empty, mud was piling up along the river, and dead fish were turning up.
"It took out one year's production," he said.
A marginal sports fishery in the reservoir was destroyed when fish were flushed down the river and several species of native fish downstream were also taken out when a layer of sediment ranging up to three feet deep settled out along a four- to five-mile stretch downstream of the dam. The sediment smothered fish eggs and invertebrates in the wetted channel, he said.
An IDFG biologist floated the river and observed dead fish, he added. "It's their provision position that any fish eggs or nests for fall spawners" were impacted. "There was definitely a fish kill."
The degree to which future years of fish production have been impacted is unknown, as there is scant information about fish populations above and below the project; therefore, the value of the fisheries lost must be estimated.
Ward said IDFG and BuRec are still negotiating a mitigation plan, but it will certainly require compensation in the hundreds of thousands of dollars and perhaps some habitat restoration.
The full extent of the damage won't be clear until after BuRec completes two more construction-related drawdowns, in 2015 and 2016. "They want a monitor to see what happens down the road," he said.
The event came as a surprise to IDFG, Ward told NW Fishletter because there was nothing about pre-construction-related drawdowns in the June 2011 draft and October 2011 final environmental assessments (EA) BuRec prepared for the work.
If IDFG had known about the drawdowns, he said, it would have done more than merely comment on the scoping document and not respond to the subsequent DEA, which received only three public comments. "In our review of the EA, there was no concern and no drawdown identified beyond regular management."
The EA was sent to 60 contacts but BuRec received only three comments--two of which were phone calls. A single drawdown is mentioned, but only in connection with the actual construction, not for any exploratory design work. The EA says only that the reservoir "would be drawn down for the penetration of the penstock and installation of the slide gate on the upstream face [and] this activity would occur below the annual tailrace drawdown elevation."
"It's safe to say there were things not factored in, in the beginning" to the EA, BuRec's Redding conceded. He said that's why BuRec last month initiated a process to supplement the two-year-old EA by adding last winter's drawdowns, the two future drawdowns and the closure of Wild Rose Park during the long construction period.
BuRec has been circumspect about acknowledging the extent of the damage. "The best thing I can tell you," Redding said, "is we understand there were some adverse impacts to the river system."
The damage got local citizens' attention. Forty citizens attended a June 25 meeting on the supplemental EA. Comments are due July 29.
Construction of the third generator is now set to start in September 2014, two years behind the original publicly-announced schedule, and will take 30 months. The improvement will increase generating capacity by 12.5 MW and add a new powerhouse, intake, penstock and other equipment. Two existing 5.1-MW units will become secondary--operating when there is sufficient load and when project flow is too low to operate the new, more efficient unit.
The run-of-river project has a net generation of 62,388,151 kWh, according to BuRec. The new unit will increase annual generation by 105 million kWh.
BuRec Project Manager Chris Vick said $40 million was a preliminary "60-percent design phase" estimate. He said the increase is due to cost refinements, software programs and "the economy starting to turn around."
BuRec spokesman John Redding said some elements of the work "weren't factored in" to the original estimate. He said it is not unusual for costs to rise as the extent of the work is better defined. He said it is possible that the final cost will be higher still.
This month, BPA said the $40-million figure, which appeared in two BuRec press releases issued four months apart in 2011, "was incorrect."
"There's $53 million of work going on at the dam," said BPA spokesman Doug Johnson. "$13 million is for work on the two existing units. But the $40 million is for what's going on at the new unit."
BPA did not disclose the estimates to its customers. The agency normally publishes the target, forecast and actual costs of dozens of ongoing capital projects in quarterly reports. Typically, a few are blocked out with the footnote that "contracts have not been awarded--cost estimates are confidential." In the last six quarterly reports, the Black Canyon estimates have fallen under this exclusion. But all of these quarterly reports were issued after the BuRec press releases which quoted the $40 million figure, as well as the one with the "correct" figure of $53 million, which was released June 13.
Vick, the BuRec project manager, said the contract for the project has still not been let, but is set to be advertised in November. -Ben Tansey
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