Tacoma Power Rep Says Dam Failure Unlikely, Lower Lake Levels Still Necessary

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MOSSYROCK — Nearly 100 people turned up in Mossyrock on Friday night for a public meeting in regard to a proposal from Tacoma Power to draw down the level of Riffe Lake by 30 feet each summer for the foreseeable future.

That audience included all three members of the Board of Lewis County Commissioners, Mossyrock mayor Thomas Meade, a contingent of law enforcement and emergency response personnel, Lewis County Emergency Management Director Steve Mansfield and a gaggle of locals who ranged in temperament from curious to concerned to combative.

Tacoma Power Generation Manager Pat McCarty began the meeting at the Mossyrock Community Center with a lengthy slideshow presentation before opening up the floor for questions from the crowd. He noted that the plan to draw down Riffe Lake in the summer is a response to updated seismic data that has indicated that the spillway piers on the upriver side of the dam might be at risk of failure in the event of a large earthquake. 

However, McCarty said that the anticipated offshore Cascadia earthquake is not the event that raised red flags for Riffe Lake. Instead, McCarty says that an “intraslab” earthquake of magnitude 7.5 or greater would need to strike within the relative vicinity of Mossyrock Dam to create serious problems. McCarty insisted that it is highly unlikely that such an event will happen, and that the dam is not currently in imminent danger, but the Federal Energy Regulatory Commission is requiring that the dam be upgraded to meet the newly minted standards.

McCarty said that if that specific set of circumstances collided during the summertime when lake levels are usually closer to 779 feet, the force could damage or break off the spillway piers, which in turn would render the spillway wide open, essentially creating four 20,000 square-foot holes in the center of the dam. In that scenario, the dam would flood out until it reached a level of 728.5 feet. McCarty said that flow would overwhelm Mayfield Lake, flooding the trout hatchery, Toledo, Castle Rock, Kelso and Longview. McCarty said that it is even likely that river levels in Portland would rise if the spillway failed with a full reservoir pent up behind it.

However, with the lake drawn down to 749 feet or lower, McCarty says that any flooding caused by an earthquake would not exceed the high flow flood of record, which was last experienced in November of 1995.

Because upgrades or repairs to the dam are subject to lengthy regulatory processes, there is no timetable for progress or completion of the project. McCarty is only willing to say that it will very likely extend into the next decade. However, the plan has not even been approved by FERC yet, and McCarty noted that it is entirely possible that the agency could ask for an even lower lake level, or added mitigation efforts for impacts to recreational resources and cultural resources, such as Native American arrowheads that will be exposed on the rim of the lake.

“We expect that FERC might ask for some additional mitigation measures which could lead to even more land closures,” said McCarty, referring to camping and other recreation areas that may be closed to prevent public access to culturally sensitive artifacts. ”We’re proceeding like 749’s going to be OK, but we have to wait for FERC’s approval before we can go ahead.”

Many of those in attendance at the meeting expressed concerns over what the lower summer lake level will mean for recreation opportunities around Riffe Lake and the corresponding effect on the economies of local communities. The lower lake level will take the fishing bridge and south boat launch and Taidnapam Park out of commission, as well as the popular Mossyrock Park swimming area and the Kosmos boat launch. Additionally, stumps and other hazards, such as island sand bars, will be exposed in the lake.

McCarty says that Tacoma Power plans to eventually make modifications to the boat launch and swimming area at Mossyrock Park that will make them more useful with the low water. However, those projects also require approval from multiple government agencies, so there is no timetable for their completion either.

“I was originally hopeful that we would have a new swim beach down at Mossyrock Park this summer, say by the Fourth of July. But once I learned that we had to go through the Army Corps of Engineers, my hopes were dashed,” he said. 

McCarty also said that any natural hazards brought to the surface by the lower lake level will likely be left to their own devices. 

“We’re probably not going to go out and do a massive stump removal effort,” said McCarty, who called the stumps fish habitat.

On the other hand, McCarty dismissed concerns raised about the impact to angling opportunities at the lake by noting that Riffe is not a managed, or planned, fishery. Instead the fish population is dependant upon sporadic stocking of surplus fish by the Washington Department of Fish and Wildlife as well as landlocked coho that manage to migrate downriver past Cowlitz Falls Dam. McCarty added that Tacoma Power still plans to stock their regular allotment of rainbow trout at Mayfield Lake, Swofford Pond, South County Park Pond and Lake Scanewa. Previously, McCarty specified that any rainbow trout stocked into Riffe Lake in the future would be pulled from the regular allotment for Mayfield Lake.

If the lower lake level becomes the “new normal,” as McCarty has called it, the lake will also see lower autumn water levels as the inflow volume inevitably lags behind the outflow requirements. Riffe Lake used to be kept at near capacity level between Memorial Day and Labor Day, but updated outflow requirements intended to benefit federally-protected fish species have gradually forced the typical summer lake level lower and lower. Last year was particularly acute as melting snowpack failed to reach Riffe Lake and the reservoir dropped to what was an uncomfortable low for many Riffe Lake regulars and business owners. 

Last year on July 4, the lake was 750 feet. Beginning this summer, that level is not expected to exceed 749 feet.



When asked by an audience member to explain what Tacoma Power would do for residents who see their property values drop due to the lower lake level and deceased recreation opportunities, McCarty was unable to provide a response. He compared the drawdown to another reservoir reduction at Cushman Lake some years ago, when that lake was reduced by 90 feet.

“There's not a lot of homes lined around Riffe like there is around Mayfield. Imagine the outcry if we drew down Mayfield by 90 feet. There would be a lot more people upset,” said McCarty.

McCarty noted an influx of solar and wind farms in California and elsewhere have caused great volatility in the power market in recent years and put Tacoma Power in an economic pinch of their own. He said many companies are currently selling power at a loss. 

“There’s this huge amount of electricity being produced and there’s not enough load for it,” said McCarty, who stated that Tacoma Power has no interest in giving away their power, or paying someone else to take it. However, he refuted the notion that Tacoma Power is drawing down the lake in order to create less power and manipulate the market. 

“We are a small player in the power market,” said McCarty. “If there is any link, it’s all random.”

McCarty also addressed questions about the potential transfer of park management from Tacoma Power to other entities. He said that currently Taidnapam Park is the only Tacoma Power park on the block and that it is directly related to the impending retirement of longtime park manager Arnie Lund. 

“I’m being asked as a manager to look under every rock for a penny that might be saved,” explained McCarty, who noted that there is no requirement for Tacoma Power to run their own parks.

Once the floor was opened up to questions and comments from the audience, Lewis County Commissioner Bobby Jackson was one government official to speak up in defense of local economies and recreation interests.

“We are talking about where we live. Lewis County is facing some serious economic challenges and tourism is one of our major economic draws,” said Jackson, as he addressed McCarty directly. “To suggest that ‘oh, well, you won’t see very much of an impact,’ is rather offensive to me, sir.”

It was a comment that drew a nearly unanimous round of applause from the audience.

Lewis County Commissioner Gary Stamper also chimed in on the developing situation at Riffe Lake and Mossyrock Dam.

“I would like the boat launches to be able to launch larger boats there,” said Stamper. “I guess we’re looking for a short term fix, if this is going to be a 10-year plan.”

Stamper echoed Jackson’s sentiment about Lewis County’s well documented economic struggles and voiced his hope that a concerted effort will serve to alert the general public that Riffe Lake still exists, and in some semblance of typical working order, so as to help stem the tide of lost tourism activity around Riffe Lake and the surrounding communities. 

“We really can’t afford another bump,” said Stamper.

For additional information from Tacoma Power on the proposal go online to MyTPU.org/RiffeLake, or, for specific questions or thoughts send an email to Cowlitz@CityOfTacoma.org.