Big Creek 1 sits on top of 60 feet of sandy material. About 30-feet of the same material fills the space between the base of the upper dam and bedrock. Consultant Verena Winters with HDR Engineering told city councilors last week that the dams might deform and fail during an even moderate earthquake. Newport discovered the issue in 2011 during construction of its new water treatment plant.

HDR’s report lays out three options to stabilize or replace the upper dam: Build on top of it or construct a new earthen or concrete dam downstream.

Lower Dam a Goner

Winters said HDR recommends removing the much smaller lower reservoir entirely.  “The benefit to fix that dam doesn’t weigh out the storage volume,” she said. “It would be way too much money for what you’d get out of this dam.”

HDR recommends constructing a roller compacted concrete dam. The concrete option has a higher seismic stability and lower maintenance cost than an earthen dam.

To meet current and future water demand, the upper reservoir would more than double in storage capacity: from 970 to 2,270 acre-feet.

“Neighborhood of $50 Million”

HDR estimates the base cost of an earthen or concrete dam at about $19 million. Design, permitting, fish passage, possible wetland mitigation and the water intake pipe to the water treatment plant add to that figure. Doubling the storage capacity of the reservoir obligates the city to construct a new access road around the west side for the Forest Service and homeowners.

Newport City Engineer Tim Gross says the cost of the entire project is “in the neighborhood of $50 million.”

Gross said that it’s not feasible for a community the size of Newport to fund such a large project on its own. The city is looking to federal and state agencies for funding.

“There is not a rock we are not turning over to figure out how we can fund this,” he said.

“We have about $450,000 in our budget this year to move forward and part of that we are going to use to try and acquire additional funding.”

The Doing Nothing Option

The Newport City council is expected to officially accept the HDR report next month and choose one of the recommended options.

Gross said a fourth option, doing nothing, probably would not sit well with the folks at the Oregon Dam Safety Program, which ranks the Big Creek dams as number two and three for risk based on the consequences of a failure.

A dam collapse would leave Newport without potable water for cooking, washing and drinking.

Scientists estimate the chance of a major offshore earthquake strong enough to break the Newport dams as somewhere between 14 and 40 percent in the next 50 years. State officials believe such a mega-quake would create mass devastation all the way to Interstate 5.

“How many people are going to be hiking to Newport to help us figure out how to get our dams working?” Gross said. “The idea is you build a dam that in theory would still be standing afterward that as a local community we’d have the ability to try and stabilize.”

Contact Reporter Larry Coonrod by emailing editor@lincolncountydispatch.com