November 19, 2001
Carnation developing evacuation route in case of dam failure
by Lisa Allen
Valley View Editor
CARNATION - Officials here are currently in the process of updating the city's emergency evacuation plan in the unlikely event of a major breach of the Tolt Dam. As part of the plan, the city has purchased 20 acres of hill property in the Tolt River Highlands for use as an evacuation area.
The city saw the need recently to update the plan after a walking trail, long-used during evacuation drills by the local schools, was closed off when the Weyerhaeuser property it was located on was sold.
For decades dam breach evacuation drills had been conducted every September by the Riverview School District. Both Carnation Elementary and Tolt High (now Middle) schools participated in the modified earthquake/dam breach evacuation drill. The earthquake drill was included because it is generally assumed that the dam would fail only as a result of a major seismic event. However, the dam has been analyzed and found safe for the maximum earthquake that could occur at the dam.
Students, upon hearing the siren, would "drop and cover," then do a mass evacuation on foot to NE 60th and east up the closest hill. But the sale of the hill property left the schools with no access to an evacuation trail that was within walking distance.
That concerned Carnation Councilmember Laurie Clinton, who 15 years ago co-founded the Riverview Emergency Preparedness Committee with former Carnation Principal Jim Jordan. Clinton began looking into the Weyerhaeuser property on the hill and, learning that three 20-acre parcels were still available, suggested that the city buy one of the parcels. The City Council agreed and the sale was finalized last month.
City officials are now working to put together a citizens emergency preparedness committee. Residents are welcome to attend two organizational meetings that will be held on Dec. 13 at 7 p.m., and Dec. 14 at 10 a.m. at City Hall.
"We are working on a plan and place to go," Clinton said. "But obviously, our true hope is that we will never need it. We have the property and what we want now is for FEMA (Federal Emergency Management Agency) to construct a trail. We would like to have it engineered as soon as possible."
City Manager Woody Edvalson said the city purchased the property for $190,000 from operating reserves out of the general fund, with $40,000 down and a five-year note with Weyerhaeuser. The city has applied for grant funds through the FEMA Hazardous Mitigation Grant Program, that was made available as a result of the 2001 Nisqually earthquake. The proposed grant application asks for $125,000 for the development of the evacuation trail, which city officials anticipate to be the most cost-effective and efficient means of moving the public out of danger in the event of such a flood. The parcel and proposed trailhead are located at the east end of N.E. 50th St.
Edvalson said the other access is a paved road off the Tolt River Road, but currently there is a gate at the property line. At the top, there is an open area where people could congregate and enough room for temporary shelter and supplies. Plans are to add concrete pads for emergency trailers and storage, he said. There are already two emergency caches located halfway up the hill and there is power to the site.
"It's safe to say that if there were a catastrophic flood, every home would be impacted," Edvalson said. "Our plan is to develop evacuation plans to move people off the valley floor to high ground. The easiest way now is the paved road, but one of the potential problems with that would be if there were an earthquake, trees could fall across the road. Our plan emphasizes walking and gives people 45 minutes to evacuate. We are also not prohibiting people from finding their own way."
Other alternatives for those in the north end of town will be considered as part of the plan, he said.
"As we go through the process we will pull in the fire department, the schools and King County to work with us on an overall plan," he said. "We recommend now that if the siren goes off, people should walk as quickly as possible to some high ground. We eventually want to develop the evacuation trail and a set of plans on how to deal with the cars that would end up at the top of the hill and also for those who are handicapped."
Seattle Public Utilities operates the Tolt Dam which provides water for about 400,000 residents of North Seattle and the Eastside. The 200-foot high dam, located on the South Fork of the Tolt River about16 miles east of Carnation, was completed in 1961 and also provides flood protection for downstream residents and controls flows for fish habitat. The area surrounding the dam and Tolt reservoir is open only to authorized personnel. In addition, security to the dam and other SPU facilities was increased after the Sept. 11 attacks.
A new dam breach warning system for downstream residents was installed in 1993 to replace an aging system. It was updated earlier this year when control of the system was transferred from the Tolt treatment plant to the SPU Operation Control Center to coincide with the opening of the new Tolt filtration plant.
The warning system consists of automated instruments and a computer controlled siren system. The sirens, tested every Wednesday at noon, can be heard in downtown Carnation and at four locations along the Tolt River Road.
The operation control center has an operator on duty 24 hours a day. Data from automated instruments at the dam and in the river below are transmitted by fiber optic cable and microwave to a computer console and siren control at the operation control center. The computer automatically reads the instruments and evaluates the readings to determine if a problem could be developing. Possibilities include leakage, overtopping, a blowout or slump in the dam crest.
If a possible problem is detected, a strobe light and horn are triggered at the control center. The operator evaluates the situation and determines if the sirens should be sounded in Carnation. The sirens can also sound automatically if the situation appears critical.
Laurel Harrington, SPU dam and seismic safety manager, said all dam structures are required by government agencies to be inspected periodically by an independent consultant and that the Tolt Dam has just recently undergone considerable seismic evaluation.
"Seismic tests proved the dam to be in real good shape," she said. "All our instrumentation was checked out ... it is all fully functional."
If the dam were to fail, SPU projects water levels of between four to six feet in downtown Carnation, and up to 10 feet east of town along the Tolt River Road, depending on conditions. Residents would have slightly over an hour to evacuate after the alarm is sounded.
"The dam would not fail immediately," said Harrington. "There wouldn't be a big wall of water coming down the valley. It would be a slow process."
But it is the scenario of seeing the entire town flooded that has the city working on its preparation process. Eastside Fire and Rescue Chief Lee Soptich, a Carnation resident, said the fire district has a response plan in its disaster manual that address 11 different scenarios, one of which is the collapse of the dam.
"In the event of a suspected problem at the dam," he said, "we would verify the problem, assist the city in evacuation, and protect the fire district's command post."
Soptich advises residents to do what they can to protect themselves, since the fire department is not staffed to be able to take care of everyone.
"People need to prepare in advance to evacuate," he said. "This is a small city. We have to rely on people doing what they can on their own."
Edvalson emphasized that preparation by citizens is of the utmost importance.
"People need to anticipate leaving their home for up to 72 hours," he said. "Other scenarios could force this, as well, such as a chemical spill on the main highway. Residents should have a backpack kit for every member of the family that is ready to go and easy to get to. It comes down to the fact that it is wise to be prepared."
Note: To get disaster preparedness material, call the King County Chapter of the American Red Cross at (206) 323-2345.