Alder Dam

Alder Dam.

FERC is investigating whether Tacoma Power's Nisqually River hydroelectric project contributed to downstream flooding in early February.

Heavy rains prompted Tacoma Power to increase spill at the project's two dams—Alder and LaGrande—starting Feb. 5. By Feb. 7, hundreds of residents had to flee their homes as the Nisqually spilled over its banks.

One resident, Howard Glastetter, filed a formal complaint with FERC, prompting the agency's inquiry. The complaint alleges Tacoma Power kept the project's Alder Lake reservoir too high despite near record-high precipitation since the beginning of the year. On top of this, a new winter storm brought torrents of rain, so the additional water and limited unused reservoir capacity "forced Tacoma Power to make a high-volume concentrated discharge" that flooded neighborhoods downstream, the complaint said.

No serious injuries were reported during the flood, but several houses were severely damaged, according to news reports.

Far from making things worse, Tacoma Power used Alder Lake to mitigate flooding, reducing downstream flows by as much as a quarter, officials for the utility said. Furthermore, several downstream tributaries contributed to the floodwaters, though most of the river's water flows through the two dams that make up Tacoma's Nisqually project. The hydroelectric project has very little storage, is not a flood-control facility and has no flood-control requirements.

On Feb. 5, Thurston County cautioned downstream residents that Tacoma Power planned to spill 12,000 cfs at the Nisqually project dams.

The next day, county officials issued a press release saying the utility planned to increase spill to 17,000 cfs and urged residents to evacuate.

Flow out of LaGrande Dam topped out at 15,000 cfs. By Feb. 7, Tacoma Power began reducing spill. By that time, though, floodwater had forced hundreds of people from their homes.

Just a few days later, Glastetter sent FERC a terse message.

"My Nisqually Valley neighborhood has just been flooded, again, thanks to your FERC/Tacoma Power" agreement "to have no winter-time maximum levels for Tacoma Power to stay under at Alder Lake Reservoir," he said.

His formal complaint followed in early March.

FERC told Tacoma Power about the investigation in an April 9 letter to the utility's generation manager, Chris Mattson. The commission asked the utility to provide by June 8 all operational data for the hydro project from Jan. 1 through April 9, any prior correspondence with Glastetter and any other relevant information.

Thurston County Commissioner Gary Edwards criticized Tacoma Power at a commission meeting soon after the flood.

"I would chastise Tacoma Power for not seeing this need to release earlier, and I'm looking for some kind of a solution there to see that [it] might not happen again," Edwards said at the Feb. 11 meeting, reported the Nisqually Valley News.

Tacoma Power officials say the utility reduced downstream flooding by as much as 25 percent by holding as much water as it could in Alder Lake. For several weeks prior to the Feb. 7 flood, the Nisqually hydroelectric project had been generating at full capacity.

The Nisqually hydroelectric project is not a flood-control facility and has no flood-control obligations. Alder Lake reservoir only has 161,000 acre-feet of storage. Alder Dam controls the Nisqually River's flow out of the lake. LaGrande Dam is a few miles downriver. There is no storage between the two.

In late January, the utility spilled water from the reservoir "to preserve storage space for additional rain," Tacoma Power said in a Feb. 14 press release.

Throughout the morning of Jan. 28, the Nisqually's flow below LaGrande Dam hovered just below 2,200 cfs. It had been near that level for three days. Shortly before noon, it started climbing. By 4:30 p.m., it hit 6,940 cfs. It was near or above 6,000 cfs until noon the following day, when it ebbed and settled around 4,500 cfs.

It spiked up again on the afternoon of Jan. 30, averaging 6,703 cfs through the night. The flow eased around noon the next day, and it settled around 4,800 cfs, according to United States Geological Survey data.

At the same time, the reservoir's height rose from around 1,195 feet for most of January to 1,204 feet on Jan. 28. The increased river flows coincided with the reservoir dropping down to 1,202 feet by Jan. 31.

But as streamflow decreased, the reservoir continued to rise, nearly hitting 1,205 feet—2 feet shy of the full level—on Feb. 2. The level declined to just below 1,200 feet by Feb. 5, when Tacoma Power started to spill.

On Feb. 6, streamflow below LaGrande was more than 15,000 cfs. Farther downstream, it topped 20,000 cfs that day. By that time, deputies with Thurston County Sheriff's Office were knocking on roughly 400 doors, warning residents to evacuate, according to news reports.

The Nisqually's main stem was not the only source feeding the floodwaters downstream.

"It's important to note that [Tacoma Power does] not control the flows of the Mashel River, Ohop Creek or other streams that empty into the river downstream of the Nisqually River Project," Mattson told Clearing Up. "These tributaries were running extremely high during the storms and contributed to the flow of the Nisqually River under flood conditions."

Tacoma Power is complying with FERC's data request.

There have been no discussions about river management with Thurston County officials, Mattson said.

In his complaint, Glastetter urged FERC to impose a maximum reservoir height of 1,197 feet between Labor Day and Memorial Day.

FERC only requires a minimum reservoir heights at Alder Lake: 1,197 feet from Memorial Day to Labor Day, and 1,170 feet the rest of the year.

He has submitted comments to FERC regarding the Nisqually project at least once before, in 2007. While serving on a Thurston County flood planning committee in 2017, he advocated for imposing maximum levels on Alder Lake and accused Tacoma Power of contributing to flooding on the Nisqually River by keeping the reservoir too high.

Glastetter's frustration was evident in the Feb. 11 message he sent to FERC in the wake of the most recent flood.

"You folks need to take a hard look at what you have allowed," he told the federal commission

Contributing Editor

Dan has covered stories from Seattle to Tbilisi; spent time with the AP, Everett Daily Herald and Christian Science Monitor; and was twice a member of a team nominated for a Pulitzer Prize. He and his wife have three young children and live in Seattle.