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NorthWestern details results of draw down tests


March 19, 2020

NorthWestern Energy met with around 25 community members to discuss results from the October 2019 operational draw down tests. The tests are needed as the company prepares to relicense the Thompson Falls Hydroelectric Dam under the Federal Energy Regulatory Commission (FERC) license requirements. The license, which expires in 2025, requires a significant amount of data to be collected from around the reservoir on NorthWestern Energy’s part.

Mary Gayle Sullivan, director of environmental and lands for NorthWestern Energy, explained the premise of the meeting is intended to be an exchange of information. “We want to refresh everyone about the relicensing process, and we want to talk about the operational test observations we made, and report back to you, which is what we committed to do last October, after the meeting,” Sullivan said.

The current license NorthWestern is operating under is from the year 1979. There was a major modification in 1990 to allow the addition of the new powerhouse, and another amendment in 2009 allowed for the addition of the fish ladder.

“What we are in the process of doing is preparing the application for a new license, and FERC administers that license,” Sullivan said. While Sullivan expressed there is quite a bit of work that goes into the relicensing application process, she also explained why they are beginning so early. “The last two years, what we have done, has really been a voluntary effort. NorthWestern wanted to hear from you and wanted to collect all the information that’s out there.” The effort made on NorthWestern’s part was to formally share all the conditions and environmental attributes associated with the Thompson Falls Hydroelectric Project. The company is now at the stage where they are preparing the formal FERC process. Sullivan said this is a 5- to 5.5-year process because of the structured rules given by FERC.

In July of 2020, NorthWestern Energy will take the first steps to officially trigger the relicensing. NorthWestern intends to submit to FERC a notice of intent to relicense and a pre-application document (PAD). The PAD will include all the information NorthWestern Energy has collected, which includes the consultations, public meetings, working with the resource agencies, any potential issues, any preliminary studies and operation scenarios. “FERC takes that, and they drive the process from there,” Sullivan said.

After the notice of intent has been filed, FERC will host a formal meeting in Thompson Falls that will scope issues that could present themselves from any impacts due to the Thompson Falls Hydroelectric Project. Sullivan stressed there will be a number of opportunities for public input over the next couple of years.

Jeremy Clotfelter, NorthWestern Energy superintendent of hydro operations and maintenance, explained how a balance of operation is needed to maintain flexibility for generation as the grid demands it. “We have in our current license the flexibility to use four feet of the reservoir,” Clotfelter said. “So, we did the tests, and from an operational perspective, as far as the plant goes, we had no issues. We were able to understand what kind of volume of water there is at different levels of the reservoir, and how much energy we can get out of that.”

Andy Welch, Manager of Hydropower License Compliance at NorthWestern Energy, detailed the different reservoir conditions during the draw down tests. Welch and his team looked at how the water elevation changed throughout the system, which included looking at the water elevations all the way upstream, down to the dam and also downstream of the dam. Shorelines were also looked at, and what happened to wildlife and water quality was also observed. “A test over a three-day period is a really short window to try and estimate what type of impact we may be seeing. We made a lot of observations and we learned a lot, but this may not be everything we could learn,” Welch said.

Tests were conducted during and after the drop, in different parts of the reservoir. “We wanted to see how things changed in different parts of the reservoir,” Welch stated. The team wanted to know how fish habitats at the mouth of Thompson River would change and “a time lapse camera was set up in place to observe and watch how that area changed relative to the habitats.” Water level changes were observed by the upstream face of the dam, by the radial gates as well as the mouth of the Thompson River. Water level changes were delayed at certain parts of the river. Welch said, “the hydrology is limiting the amount of water surface drop in the upstream locations versus the downstream locations.” The team observed the water level changes took longer to drop upstream. Below the dam and powerhouse, similar observations about water levels were seen.

Kim Bergstrom, a recreation planning consultant for NorthWestern Energy, shared observations taken from a recreation and aesthetics standpoint. Pictures were taken during the draw down in order to see the impacts on the shoreline, public access areas and private docks. One of the pictures shown was the boat launch on Cherry Creek. “You can see the angle of incline of the floating dock was quite steep,” Bergstrom said. She stated there were many areas that were completely exposed, and a lot of the docks would be out of water during a four-foot draw down. Two days later, the two-foot observations were taken. “The ramps were in much better shape. A lot of the area that had been exposed during the four-foot drawn down were again submerged,” Bergstrom said.

Jordan Tollefson, water quality specialist for NorthWestern Energy, shared the observations made about shoreline stability around the reservoir, turbidity and water chemistry around the reservoir. “One thing we did note, in areas that had a lot of native vegetation, tree shrubs and a lot of strong root binding vegetation, it seems to really hold that shoreline together well, and you could tell those areas were very stable,” Tollefson said. The take-away from Tollefson and his team was as far as shoreline stability goes, natural trees and native shrubs along the shoreline, increase shoreline resiliency.

The conclusion the team came to was that there was no significant change in the water chemistry during the operational tests. “We didn’t see much, which is very telling as to the water quality of the river, and the reservoir, Tollefson expressed. Eight days later, after the reservoir had stabilized, samples were collected again, and the team saw about the same thing. All samples were below state water quality standards, and Tollefson didn’t see anything of concern.

Jon Hanson, biologist for NorthWestern Energy, discussed observations made from the fishery standpoint. Tributary confluences, fish ladder operations and fish stranding were the three main focuses for his team. Thompson River and the Cherry Creek confluences were observed during the tests. “It’s important to make sure the fish have the ability to move up into the tributaries, and then back out,” Hanson continued. Hanson’s team saw that no matter what elevation the reservoir was at, the tributaries were accessible to the fish.

In conjunction with Fish Wildlife and Parks, fish ladder operations were observed during the draw down. As the reservoir was dropped one foot, operations within the fish ladder began to change within the pools. The elevation within the pools dropped two to three inches as the elevation was reduced. Hanson said the hydraulics changed within those pools as there was less water feeding the fish ladder. Two feet below normal operation levels, Hanson saw other issues. There was not enough water being fed to the feeding pumps in the fish handling station. “Although there was still water running through the ladder at a reduced rate, some of the mechanisms to actually work up fish were inoperable, and that obviously continued into the three- and four-foot water drop levels as well,” Hanson stated.

The last major concerns Hanson and his team wanted to know was if fish stranding occurred during the operational tests, at what reservoir levels did this occur, and at what scale. The four-foot draw down exposed a considerable amount of shallow water habitat, and stranded fish were found throughout different locations. Hanson noted at the two-foot level draw down, “there were a lot less habitats that were exposed.” Types of species of stranded fish that were seen included: pike, large and small mouth bass and pumpkin seed. The majority of what they saw were native suckers and pike minnows.

“Most of these fish were no longer than two inches, so most of them were juveniles,” Hanson said. The largest fish they observed was a stranded pike that was seven or eight inches long. There was considerably less stranding at the two foot draw down. However, questions arose when the team didn’t know if the stranded fish were from the four-foot draw down two days prior to the two foot draw down. More observations and studies would be needed to find conclusive answers. In conclusion, Hanson said additional evaluations are needed to better understand the short versus the long-term impacts to the fisheries. He also said the fish ladder would need some adjustments, were they to do any kind of draw downs in the future.

As the meeting came to an end, Clotfelter expressed NorthWestern’s desire to be completely transparent as they did these operational tests, and to show the public what they saw. “As far as the future proposed operations go, in the PAD, NorthWestern Energy will be proposing a two-and-a-half-foot elevation to set the stage for future studies,” Clotfelter told the meeting participants. Which they believe will be the most beneficial to them and their customers. “We understand there are impacts, but we believe there is an appropriate middle of the road for everyone,” Clotfelter stated. As for anyone who has questions and concerns as to the future of the reservoir, Clotfelter told the group to become involved in the process that will be happening within the next couple of years.


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