Friday, March 29, 2024

Eightmile Dam still a danger, but it is getting better

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A public meeting was held on May 14 at the Chelan County Fire District 3 to discuss the situation at the Eightmile Dam in the Alpine Lakes Wilderness. The dam has been in danger of breeching due to the potential for increase snow melt around the watershed, which was impacted by the Jack Creek Fire last fall.
A breech could be devastating for those with homes along Icicle Creek, but it appears the danger is lessened now due to work done at the dam and also the fact that a good portion of snow in the watershed has already melted.
Chelan County Sheriff’s Sergeant Kent Sission of Chelan County Emergency Management moderated the meeting, which included officials from the Icicle Irrigation District, Dam Safety, National Weather Service, Forest Service and Anchor QEA Engineering.
Sisson said the conditions at the dam are currently Level 2.
“This was confusing to the public because we talk about wildfire one, two and three. This is not wildfire. This is the status of the dam at Eightmile lake is Level 2, which means it has reached a point where we collaboratively feel it more so than just an advisory of an emergency situation,” Sisson said. “The dam is not breached. There was a rumor going around Leavenworth today we have issued evacuation notices. I don’t know where that started. It’s not true.”
Sisson said they went out and talked with anybody who was within the inundation area. They’ve also taken a lot of phone calls.
“If we get to a Level 3, which when the water reaches to the top of the old historic spillway, that puts us at a Level 3. We’ve agreed that puts us in a place where we would issue evacuation notifications. It is not at that level,” Sisson said.
Icicle Irrigation District Manager Tony Jantzer said the lake level had dropped during the recent cool spell so it could be considered Level 1. He said it is about 4-5 feet below what would be considered Level 3.
Sisson said they are staying at Level 2 because there was a forecast of warm weather with rain coming after. He said it was a real collaborative effort between Icicle Irrigation, Dam Safety, Emergency Management, Forest Service to get to a point where they could get monitoring in place so they could get an engineering plan in place to mitigate the emergency circumstances.
There was a lot of snow in the watershed over the lake this year, Jantzer said.
“The south facing slopes of the watershed is probably 90 percent melted right now. The lake melted off completely sometime last week. There is no more ice on the lake,” Jantzer said. “The north facing slopes are still probably 70 percent laden with heavy, wet snow. If we get some rain up there, we could see increased flows.”
The dam, which was built in the 1920s, has been able to hand normal spills, but then in 1990, there was a big flood which pushed the dam past its capabilities to spill. That year, part of the earthen dam washed away, but it has stayed stable since then, and continues to act as a secondary spill.
The dam hasn’t changed much over the past 28 years, Jantzer said. It has been holding up well and nearly every year gets water over the earthen portion of the dam.
“What we were concerned about, based on the BAER (burned area emergency response) report in February, March. This burned area is going to generate a lot more runoff that normal, like double,” Jantzer said. “If we have any kind of event, it would push the dam to a maximum amount, we could water levels going over the dam which the dam was in no way ever designed to cope with. We are concerned about that, which is why the district declared an emergency.”
Jantzer said they are not too worried about it if things stay normal and it doesn’t get too hot. The problem would be a hot trend followed by a big rain storm. Last week, he said they flew an excavator to the site for some emergency work.
Their ultimate hope is to replace the dam entirely with a new, modern dam, but it is looking less likely like they’ll be able to do that this year.
“In the interim, to try to make things safe for everybody, we’re going to rip out most of the old earthen dam. We’re going to take that down to the area that was already washed down,” Jantzer said. “We’re going to harden that with all the rock we can find up there, make it so it will handle a 2-3 feet going over it. We’re going from a 30-foot wide spillway to over 100-foot wide spillway.”
By doing this work, Jantzer said instead of eight feet going over it, it will be a couple feet, which should be able to handle four times as much water. This work was to be done last week. There is a portion of the wall of the dam that concerns Jantzer.
“It was designed to have a dirt back. Now, it is a free standing masonry wall. It has water that will pass on both sides of it. If we get significant flow, water will be passing quite deeply on the other side,” Jantzer said. “Because of fire and we get a big runoff, we figure it will be a lot of debris. It will pile up against this wall. It wasn’t designed to be free standing. One of the first things we want to do is break that wall off at the level of the rock.”
Jantzer is hoping, when they are done there, there will be nothing for the debris to catch on. It will just pass through into Eightmile Creek. Anchor QEA is the engineering firm hired to put together a mitigation plan for the dam.
Engineer Dave Rice said they have been consulting with Dam Safety and others on what can be done to lower the lake to reduce the risk of breeching the dam. Then, eventually, work toward a more permanent solution. Dam Safety asked them to come up with an interim plan.
“We developed three steps of action. The first steps is what Tony described, which would be taking the top off the wall, then creating this larger spillway on what’s left of the earthen portion of the dam,” Rice said. “Then, hardening that with as much rock as we can find. We hope to have that done this week. That is step one. It’s all that Dam Safety has approved us to do at this point.”
Through consultation with Dam Safety, Rice said the next step would be to install some pipe there to create a temporary siphon to help draw the lake down. So if the lake is drawn down, there is more of an ability for the lake to capture the runoff that comes into it, making it less likely for the lake level to rise where it becomes a dangerous situation.
The third step would be making that emergency siphon a little bit more useable over the coming months or as long as it takes before there is a more permanent solution.
“There is a condition at the dam with this low lying pipe that has been there since the it was constructed. It was blocked. It was constructed out of wood and concrete. The boards that are part of this pipe, it’s only currently letting through about 4-5 cfs when it has a capacity of over 50 cfs,” Sisson said. “That’s an issue where we can’t relieve the current impounded water like we could if that pipe was free and clear. That’s why we’re talking about a syphon taking pressure off the lake.”
Jantzer said they are hoping to unplug that pipe once the lake goes down. At that point, he said they have the ability to release 100 cfs out of the lake so they have a lower pool in the lake. With the water in the lake above the outlet pipe, he said they can’t get inside the pipe to unplug it.
“Debris has plugged it up mostly. We do believe we can unplug that. With the siphon and that going, we should be able to hold the lake down until we get some kind of an extreme event,” Jantzer said. “That would give us a lot of good cushion for an extreme event so it won’t go over the dam.”
A perfect storm of a giant rain cell over the watershed could bring it to a point where it rises to Level 3, Sisson said, so that’s why it is important to have some monitoring up there. This is being handled by Dam Safety, which is part of the Washington State Department of Ecology.
Joe Witczak, WSDOE Dam Safety and Wells manager, said access to the site is complicated. There is no dam tender there, which is a concern. Witczak said they want to be able to monitor the lake so they know what level they are at, one, two or three.
The priority is to get a lake level monitor in there, Witczak said.
“We’re actually partnering with the Sheriff’s Office which is going to provide helicopter support, so we can put lake level monitoring equipment up there. Then, DOE has staff that will get up there and install that. Once that equipment is in place, then we’ll get a reading about every five minutes about what the lake is doing,” Witczak said. “The National Weather Service will be watching that for us, looking at triggers, then getting back to Tony (Jantzer) and Chelan (County) Emergency Management and myself about what is going on at the dam.”
Dam Safety would also like to monitor the actual flow coming from the dam, from immediately below the dam and another around Little Eightmile Lake. He said this will happen as they buy, build or steal the equipment from another site in the area.
Witczak said they also want rain gauges up there and cameras.
“Ultimately, we want to get a camera up there, so when you see that lake level move, you don’t always know why it is moving. It could be a log bumping up there. It could be a temporary situation and not like the dam is failing,” Witczak said. “Having eyes on it would be really helpful. The DOE is looking to purchase this equipment. It’s about $15,000 worth of equipment. We would loan it for the site to use until some other mechanism is available to do that monitoring. Then, we could use it at other dam sites.”
Katherine Rowden with the National Weather Service said they don’t have great radar coverage in the mountains there, so they’ve deployed rain gauges over the years.  
“We know how to make it work once the gages are out there. They transmit hourly until they reach the thresholds, then they’ll transit more rapidly. Our office is staffed 24/7 and we’ve set up internal alarm on our forecaster’s stations so they can see that,” Rowden said. “We try to set those thresholds lower than what might be the level of concern. We issue flood warning for dam failures but that is when somebody tells us the dam has failed. This is an unusual situation where there is nobody at the dam telling us it has failed.”
Emergency Management released inundation maps to generally show what could happen with a complete dam breech. It shows outside the normal channel of the Icicle Creek in the low lying areas that would see inundation.
There are 12 dots on the maps showing residences they feel would definitely be inundated.
“This isn’t an exact science because there are so many different formulas. How high is the Icicle Creek at the time the dam breeches? Is it a complete dam breech or partial dam breech?,” Sisson said. “Out of the extreme caution, we notified around 50 residences from Eightmile Creek to the Forest Service Campground down past the Fish Hatchery. We’ve made as many contacts as we can. We’ve found many of the residences are part time folks. Nobody home, so we’ve left fliers. We’re trying to reach out through other means.”
Chelan County Sheriff’s Deputy Rich Magnussen of Emergency Management said the public notification system used in the county is called Alert Sense.
“A lot of you have probably already experienced it during fire season. We put out our evacuation notices through your cell phones or landlines,” Magnussen said. “If we get notified from the weather service that monitors have picked up a big flow in the river or drop in the lake that a significant incident has occurred, we trip what is called an iPause message.”
That iPause message would push out to every cell phone and landline in the area where something might be happening, which is basically an evacuation notice.
“That way, nobody has to sign up for that at all. That goes out automatically. There is a way to sign up to get some non-critical messages, public meetings, etc. Go to our emergency management website. There is a link on there to sign up. Click on Eightmile Dam,” Magnussen said. “We will be doing door to door notifications. This does not take the place of that. As you’ve heard, we don’t have a lot of time if we do have a big event up there to get a bunch of volunteers and deputies together to go door to door. It does take time to get that together.”
If there was dam breech, Sisson said they would put out alerts and try to go door-to-door but they will have only about 30-45 minutes between the time of the breech and when the water hits the Wenatchee River.
“We’ve had a response meeting with Fire District 3 and other responding agencies about how that would work. We want Fire District 3 to go directly to Icicle Island. My concern there is the one bridge ingress, egress,” Sisson said. “Most of the homes sit above the inundation area, but we don’t want people stranded out there. We would automatically notify our swiftwater team, whether they are needed or not. We going to activate them anyway. They are trained in water rescues.”
Eightmile Lake is within the boundaries of the Wenatchee River Ranger District. District Ranger Jeff Rivera said they have been working with Dam Safety, their own regional dam safety and their wilderness folks on this issue. They’ve completed a minimum tool analysis.
“What complicates things is this is in the wilderness. By law, we’re required to do this minimum tool analysis to determine which tools we can use in the wilderness,” Rivera said. “That was completed for the use of the monitoring equipment.”
One of the issues that has come up is public access, said WRRD’s Brian Mulligan.
“Right now, we’re allowing access up the Eightmile Trail into the lake. We’re going to open the campgrounds as normal,” Mulligan said. “We’re following the same emergency protocols. At the point, it becomes a Level 3 emergency, the campgrounds will close and we’ll remove people out of there. Prior to reaching Level 3, if there is high probability of reaching Level 3, we would close the trailhead.”
Ian Dunn can be reached at 548-5286 or editor@leavenworthecho.com.

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