The Newport City Council got an update this week that they probably didn’t want to get. City Public Works Director Tim Gross said a structural evaluation of both the upper and lower Big Creek Dams produced good news but also some really bad news.
The good news is that the dams are structurally okay for how they were built. But the bad news is, the dams will not survive a Cascadia Subduction Zone earthquake. Maybe not even a moderate one. If that happens both dams very likely to fail. In addition to the horrendous damage inflicted from Big Creek Road down to Agate Beach, it’ll mean that Newport’s water supply will be literally gone.
This bleak report was given during this week’s Newport City Council meeting as an update from Gross. He said the final report on the structural condition of the dams will be given in a couple of months. Gross told the council that the dams were well built, based on what was known at the time of their construction – the upper dam built better than the lower one – the lower one built decades earlier.
But since the development of information about Oregon’s offshore subduction zone plate tectonics, the consultant’s report clearly shows neither dam could survive a subduction zone quake. They strike roughly every three to four hundred years. The last one was in 1700. That puts the coast at year 315.
Gross says he’s still analyzing the data and formulating a number of options for the city council’s consideration. He says he’s working closely with a number of state agencies that are also analyzing the potential threat of a large earthquake and hopefully determining what structures might survive with strengthening and “hardening.” State funds are becoming available under the heading of producing what’s called “structural resiliency” for coast and valley roads, bridges, dams and highways, to give them enhanced survivability so that repairs could be made as quickly as possible following the quake.
Gross said he expects government grant money will be made available to help strengthen and harden coastal infrastructure so local communities don’t go bankrupt trying to better prepare their communities for “the big one.” But he adds, that his city council will have to grapple with whether it’s worth launching a “many tens of millions of dollars” retrofit while knowing that possibly even that may not save the dams when the big one hits. He says it’s a financial continuum from doing nothing to strengthening the dams we have, to building a completely new dam – obviously with massive cash infusions from federal sources.
Gross said it’s a huge decision that will take time. But even after the decision is made Gross says it’ll take years to secure funding to either strengthen the dams we have to building a new one, possibly downstream from the upper dam.