Mossyrock Dam on the Cowlitz River sits at the west end of Riffe Lake. / Courtesy photo by Tacoma Power
By Sharyn L. Decker
Lewis County Sirens news reporter
CHEHALIS – Recently revised earthquake predictions, which portend failure of the spillway gates of the Mossyrock Dam have prompted the the dam’s owner to begin considering seismic retrofits.
In the meantime, Tacoma Power plans to keep less water in the reservoir which is Riffe Lake to reduce the amount of downstream flooding if a big one should strike.
Tacoma Power announced this week the changes it is implementing.
They want to keep the level of Riffe Lake 30 feet lower than normal, according to Chris Gleason, the community and media services manager for Tacoma Public Utilities.
The United States Geological Survey recently revised its earthquake predictions for the Cowlitz River basin, information that was passed along to the owner of the hydroelectric dam in November, according to Gleason.
Riffe Lake, more than 23 miles long, is 778.5 feet when full.
The probability of a large earthquake is low, and the issue isn’t the dam itself, according to Tacoma Power.
But, preliminary analysis concluded that specific seismic events could render the spillway gates useless, which could cause considerable downstream flooding, according to the utility.
A spillway is the part of the dam that water flows through. The four spillways are located high in the middle of the dam.
According to Gleason, they’ve submitted their plans to the Federal Energy Regulatory Commission which will review and accept or modify the proposal.
They are required keep the lake below 745.5 feet during December and January, so it’s currently close to their lower level proposed, and they will maintain it there for the foreseeable future, according to Gleason.
The new lower level is expected to be in place into the next decade.
Mossyrock Dam, a concrete structure completed in 1968 is the state’s tallest dam. It produces enough electricity for 78,000 homes.
No concrete arch dams have failed due to earthquakes, according to Tacoma Power.
Boating, swimming and fishing will remain possible on Riffe Lake, but access could be limited.
Two Tacoma Power-owned boat launches are anticipated to be usable during the summer, but two others will be closed. They are considering a new swim beach at Mossyrock Park.
The seismic retrofits they are beginning to consider won’t take place for years. The development and implementation of possible solutions involves substantial analysis, planning and federal approval, according to Tacoma Power.
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On the east side of the dam are the piers that hold the spillway gates in place. / Courtesy photo by Tacoma Power
Tags: By Sharyn L. Decker, news reporter
There is one positive aspect here. I had the day off and after only a couple of hours found more arrowheads and fishing lures than I would have with a full lake. Might turn into quite the tourist attraction to go out arrowhead hunting.
They need to get final approval from the same Federal Government who approved the original plans as being safe. WTF?
Excuse me, “just for men,” but the mud flats are always open and it is the last place around here you can camp for free, Year Round. When the water level is low there is even more camp spots, so not sure where you get your info. And to whom ever wrote this post, isnt most all of this dams power shipped out to 78,000 homes towards California? If not then I would like to know why in the f*** did our rates go up 30 percent when the cowlitz dam was put in. We should almost have free power for god sakes, we have 3 dams within a 20 mile radius. Explain that please.
I’m so old I can remember when tacoma city light bosses were all about finding solutions and dedicating resources to fixing anything that stood in the way of making electricity.
Now it’s all about politically correctness and ignoring problems until they can retire.
From the builders of dams to the twiddling of thumbs in one generation; but we’ll study that…..
Tearing out the dams is the dumbest idea since Obama care. We should be squeezing every recreational and economic opportunity out of these lakes. most roads around the lake are blocked, mud flats are closed, campgrounds and boat ramps charge exorbant fees, no atv trails or free camping, rope swings constantly cut down, low cost recreational activity has taken the back seat to keeping up with the jonses’ and safety, privatization of public land with no or restricted access, you can’t enjoy either lake without cowering down to the drunk pontoon elite and their fifth wheels, the lake levels are so low the alternative lake mayfield will be overcrowded and overused, most places have no overnight camping, low water levels pose a greater safety risk and will increase lake temps and destroy fish population. I can’t think of any way anything has been managed correctly for years. it’s not uncommon for finanially strapped community elite and triple retirees to join the “cowlitz river project” for their new ‘take home’ truck fleet and excellent benefit package and light duty work load. Squandering the communities out of anything but lost recreational opportunities, harassing any one who dares to take advantage of them.
We need more horseback trails and atv parks. This is not a national park or environmental sensitive area. There are no sea run salmon or endangered species present. Thank you. Hippies. Quit messing with my back yard. Hatchery runs are ‘missing’ and game wardens targeting father son fishing trips. Sure know how to screw it up for everyone. Sure, Replace those spill way fins on the dam. Won’t change the fuckery and mismanagement lakeside cronies have perpetrated in recent decades.
Someone should have drowned the first Tacoma City Light person to mention a dam on th Cowlitz. They came right in and stole property from local residents for something that wasn’t needed. I hope some day that the Feds refuse to renew all of their permits and make them remove the illegal dams.
Either way power ratemail increases will be justified by Tacoma. Might as well take it out if they aren’t going to use it much. Rife school district probably needs renovation, better draw up a bond proposal.
Makes total sense kill the fish, loose the recreational and economic value to the community and loose the power producing ability of the dam for something that may not happen!! Liberals in charge! I say leave it. I heard they discharge most water without even producing power because maintaince on the turbines is too high or when they do its only 25% total capacity. Lol Hello, I think your talking yourself out of a job and loosing payback on the project, making the cost/benefit look like failure. Dam workers lost their lives and were entombed in concrete from the construction. That is the finest dam in south west Washington. What a waste Tacoma liberals are in charge and use the power in other counties other than here! After they fix it the next stage will removal of the dam altogether in favor of more expensive power. Go ahead loose a couple million more fish at the hatchery and blame it on the republicans in charge. Scum bags.