NEWPORT — The city is moving forward alone on a water rights application at Rocky Creek, a secondary location for building a replacement dam instead of Big Creek Dams, according to city officials.
The regional water rights application is for 9,000 acre-feet of water with a drainage basin of 5.3 square miles, 12,000 acre-feet of runoff a year and 195 acres of a reservoir area.
While the cost of building a new, earthquake-resistant dam at Big Creek, where the dams currently are, is less than building a new dam at Rocky Creek, Newport city officials still want to keep the Rocky Creek location open as a replacement site for building the dams, even if the dams end up going in at Big Creek.
“In 1997, they had a rough number put together,” said Tim Gross, Newport city engineer. “Without design or geotechnical engineering work in the analysis, that number was $40 million. But I’m willing to bet now it would be larger than that and would be $100 million.”
The costs might prove too prohibitive to move forward on constructing a new dam at Rocky Creek, located on the north side of Cape Foulweather — at least if the city attempts to do it alone. The city previously discussed building the dam with Lincoln City officials and those at other water districts in the county, who were part of talks that lasted for around 20 years.
With Lincoln City pulling out of the water rights application after developing water resources individually, city staff in Newport see the move from Big Creek dams to Rocky Creek as challenging.
Logistics and the possibility of a water main failure during a major quake are also barriers to effectively building a dam at Rocky Creek. Transporting water from Rocky Creek to Newport would be expensive and without partners to shoulder the burden, the city doesn’t have the resources to build a new Rocky Creek Dam on its own.
“To transport water from Rocky Creek to Newport, there are several slide areas,” said Gross. “Inland, there’s a lot of terrain to be dealt with.”
One facet of the Rocky Creek location that local officials deem ideal for dam construction is the Rocky Creek area laying on a basalt rock foundation, providing enough sturdy support to ensure erosion and earthquakes don’t impact the Rocky Creek site as much as the Big Creek site. The creek, in addition, isn’t accessible to salmonoid species.
Rocky Creek was one of three locations local officials identified as prime land for a new dam — Big Rock Creek and Big Creek were the other two. After a 1997 study reflecting those results, Newport and Lincoln City jointly applied for water rights on Rocky Creek, according to a review of the study performed in March 2007.
A second storage project can be built in that basin, to be filled with water from the winter season. That water would be pumped from the Siletz River through a two-mile pipeline, according to Rocky Creek project documents. Water from a potential Rocky Creek dam would be transported to existing treatment systems rather than be treated at the source, those documents say.
A memo from Corvallis firm Fuller & Morris Engineering, a geological engineering company, dated Sept. 28, 1998, said the dam site was considered “good” and the reservoir site was considered “acceptable.”
“The rock at the dam site is a volcanic breccia or agglomerate that forms a narrow canyon with steep side slopes,” the memo read.
The memo goes on to say the dam foundation is strong, the seepage potential is low and the topography is favorable for construction of a dam site and reservoir. There are no unusual hazards and construction considerations were ordinary, the memo concluded.