Seattle, suburbs would lose all water pressure within 24 hours of catastrophic earthquake, city study says
As
With
"For this very catastrophic earthquake, we're looking at very significant impacts," said
The study says a disaster on par with the 2011 quakes in
The magnitude 7 quake that struck near
"Like in
SPU paid five consultants
"It's very disappointing to hear that SPU is not being forthcoming," Miles said. "The majority of the analysis is not sensitive enough to keep hidden."
Chen said the secrecy is necessary because some portions of the report contain information about vulnerable points in the water system.
The analysis examines the impacts of a magnitude 7 earthquake on the Seattle Fault and a magnitude 9 quake on the offshore
Those breaches, combined with potential problems at SPU pump stations, reservoirs and elevated tanks, likely would result in SPU's direct-service water system losing pressure in 16 to 24 hours.
Every
Most serious would be leaks and breaks in the large transmission pipes, some more than 100 inches in diameter, that move water from SPU's mountain reservoirs in the Cedar and Tolt watersheds to the cities.
Repairs to the system's smaller distribution pipes, which carry water to customers, could start almost immediately. But as many as eight weeks would pass before SPU could start repairs to transmission pipes at underground river crossings and on steep slopes, according to the study.
The transmission-pipe problems would render SPU unable for more than three weeks to start supplying water again to most or all of its suburban customers, according to the utility. The study didn't even look at what would happen to distribution pipes in the suburbs.
"It's likely that we'll lose either the Cedar or Tolt transmissions systems or both," Chen said. "That the Eastside supply line might not be available to us. That we'll have significant distribution-pipeline failures."
The analysis does not include
Secrecy questioned
SPU is citing a
Other utilities, including the
Former
SPU is asking for an enormous investment and the public deserves to know more about what the utility intends to do with that money and how the cost estimates were developed, Mullen said.
"It seems to me there's no good reason not to share the whole thing and just block out those things that are really sensitive concerns," he said.
Responding to questions from The
Growing knowledge
The last analysis of earthquake damage to
But the city still has a long way to go to protect its water system from devastation, the new study says.
The city's newer reservoirs, such as those under
In a Seattle Fault quake, the shaking could last 15 to 40 seconds and be six times as strong as during the 2001 Nisqually quake. In a subduction quake, the shaking won't be as intense but will last several minutes.
SPU's consultants used seismic-hazard maps to identify areas where permanent ground displacement likely would occur, and visited those areas to judge whether the pipes would break.
They determined upgrades are needed in a number of locations, including sites where transmission pipes cross under the Cedar, Duwamish and Green rivers.
"It is likely that both earthquake scenarios would have a significant impact on the major transmission pipelines," the study summary says.
The consultants analyzed the distribution pipes separately, determining about 2,000 repairs would be needed after a
In addition to Sodo and Interbay, the areas most vulnerable to distribution-pipe breaks caused by liquefaction or landslides include Alki, South Park and
SPU would try to keep water from draining out of reservoirs by shutting valves, Chen said. Those reservoirs could be a source for firefighting in the immediate aftermath of the quake, he added.
Investments needed
Were a catastrophic earthquake to hit today, SPU would need 18 to 35 days to restore water service to 70 percent of its direct-service customers and as many as 80 days to restore service to all of those customers, according to the study.
The recommended upgrades would allow the utility to maintain service for some customers after a severe quake and to restore service more quickly, the study says.
If all the fixes are made by 2075, service to 70 percent of direct-service customers could be restored in 11 days, with all of them back online within 45 days.
But the work would be expensive, including an estimated
SPU recently installed quake-resistant distribution pipes for the first time, laying them along three blocks of
The Japanese-style pipes have special joints that rotate and telescope during earthquakes to prevent breaks. They cost twice as much as regular pipes and also are more expensive to install, according to the utility.
Under a project schedule accompanying the study, SPU would start slowly. The utility would spend less than
From then, SPU would spend
"What we're trying to do is prioritize the most important upgrades ... and then spread out some of the less critical upgrades," Chen said.
For now, the utility is committed to a six-year business plan approved by the
The political challenge will be balancing earthquake risks against what ratepayers can stomach. The monthly cost of water, wastewater, solid waste and drainage at a typical
Seismic upgrades aren't the only projects driving up water rates. Moving ahead, SPU expects to spend about
"We need to do these seismic upgrades," SPU general manager and CEO
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