Emergency declared for dam at Eight Mile Lake

The Icicle and Peshastin Irrigation Districts last week declared an emergency related to the dam at Eight Mile Lake. The dam itself, which was constructed in the 1920s, has not failed, but now it is being threatened due to the impacts of the Jack Creek Fire last fall.
The fire burned through a significant portion of the watershed above the lake. Tony Jantzer, the manager of the Icicle and Peshastin Irrigation Districts, said they were not initially concerned about the fire.
“After a severe burn like that, the Forest Service will do a severity burn analysis. We received a draft report in January. We forwarded that to the Dam Safety Office within the Department of Ecology,” Jantzer said. “They did an analysis. Based on that report, they are upgrading the danger classification from a low risk hazard to a high risk hazard.”
Jantzer said there are two major concerns.
“With a fire like that, it burned up a lot of the vegetation, so the snow melt will happen a lot faster than normal. Secondly, when it burns severe like it did, it also bakes the soil, causing it to lose absorbency. Rain and snow melt won’t soak into the ground, it will just run off. Both of those things are going to push runoff, so it will be higher than normal,” Jantzer said.
If the dam suffered a catastrophic failure, Jantzer said we could see flows as high as 20,000 cubic feet per second or 8,976,000 gallons per minute coming out of the lake. Historic flows on Icicle Creek are around 15,000 CFS.
The dam would most likely fail during a high water event during a time when Icicle Creek is flowing already at 10,000 CFS. Adding 20,000 CFS from a catastrophic dam failure and Jantzer said you could see the highest ever recorded flows.
The old dam is in poor condition. Jantzer said the districts have been thinking about replacing it for some time.
“The lake was originally designed with only a 20-foot spillway. It has sustained some damage over the years, which is an ongoing type problem,” Jantzer said. “The earthen part of the structure has been over-topped many times. Now is about 5-feet lower than it was originally, which has helped. It acts like a spillway now.”
Since Jantzer has been the manager of the districts for the past seven years, he has not seen much change at that dam. He said they have been working on plans to replace dams in the high lakes, but because they are located in the wilderness area, there are political ramifications.
“With all those concerns, we’ve been going slow, trying to make sure everything is working right. It’s one of the major projects within the Icicle Working Group scope of work. We’ve been hoping to get it fixed that way, but based on the fire and the danger, we just can’t do that. We’re going to have to go fix it,” Jantzer said.
The lake is currently seven feet below the full mark. The districts are planning to lower the lake another 13-15 feet before the major runoff happens.
“Right now, we have it as low as we can get it. Basically, in the dam, there is a big notch, where we put check boards in to raise and lower the level so it spills over the spillway. We have all those boards removed so the water is currently just barely going over the spillway,” Jantzer said. “That spillway is about seven feet lower than the normal spillway. The water is about seven feet lower than the top of the dam. That is all we can do right now.”
The lake is currently frozen solid with a foot of ice over the top. The valve to release water out of the lake is underneath all that ice, he said. The second problem is the outlet pipe that goes to the value is plugged, so they have to go up there, unplug the pipe and open the value.
“We plan on doing that, if we can work things out with the Forest Service, and the conditions allow in May. The highest runoff in that watershed hits in June,” he said.
Of course, right now, it would be a very difficult hike up to the lake due to the snow. Jantzer said that is why they are waiting. He said they are going to need an excavator at the dam. The plan is to do the work on the dam this fall.
“It’s partially concrete, masonry and earth now. The actual design of the dam, we are going to bid things out. We are going to look at the bids then select an engineering firm to design the dam. We will build whatever they say we can build. Most likely, it will have a concrete core,” he said.
In order to do the work, the districts must go through the State Environment Policy Act or SEPA process, which can take months. Jantzer said that is why they declared an emergency, so the SEPA process can be sped up.
“We’ve already sent a SEPA checklist that we filled out to the Department of Ecology. The WAC (Washington Administrative Code) specifically states that if you are working on a dam with a storage capacity of over 40 acre feet of water, the Department of Ecology is the lead agency on that,” Jantzer said. “Right now, we’re still looking to see who in the Department of Ecology that lead agent will be. We sent it off to them and we’re waiting for a response.”
The lowering of the lake should likely will not adversely impact the district, he hopes. Right now, there is 100 percent of normal snowpack. Jantzer said they are expecting a good, normal water year.
The lake is generally used for low water years.
“If the water year is normal or above normal, it shouldn’t affect us at all. If it is below normal, yes it could affect us,” he said.
The Eight Mille Lake trail is a popular one during the summertime. Jantzer said they are in discussions with the Forest Service about closing the lake for the summer, based on the potential danger and the fact they will be working up there all summer.
“That is a possibility. We haven’t determined that yet. They’ll probably leave the trail open so they can go to Little 8-mile so they can go up to Lake Caroline. There is some discussion on closing the Eight Mile Lake trail, but that is up to the Forest Service,” he said.
To fund the dam replacement project, Jantzer said they have emergency funds set aside but they will also be looking for some funds from the state to help.
“We trying to get a grant from the DOE to help us with this. It’s a water storage thing. This just doesn’t impact the district but the whole watershed. We feel hopeful to get a grant to pay for the bulk of it,” Jantzer said.
There are currently seven reservoirs within the wilderness. Jantzer said they represent the only water storage within the Wenatchee watershed. Of those reservoirs, Eight Mile Lake has the highest refill ratio, meaning it is most likely to refill even during extreme drought.
Currently, the districts are creating an Emergency Action Plan with assistance from the Chelan County Emergency Management, DOE’s Dam Safety Office and Forest Service to notify potentially affected property owners.
Ian Dunn can be reached at 548-5286 or editor@leavenworthecho.com.