Protecting Carson City, especially the west side, from 100-year storm flood waters pouring out of Ash and Kings canyons could cost anywhere from $9 million to more than $30 million, the preliminary estimates show.
After seriously discussing storm drainage for three years, engineers this week for the first time attached dollar figures to how much it would cost to control the flows of the creeks from Ash and Kings canyons as they work their way through the city.
In essence, the bigger the dam at the canyon mouths above Longview Drive, the lower the price. A dam in a residential neighborhood, however, doesn't add to the scenic pleasures of the upper west side.
"If I look up at a 40-foot dam, my house would be dwarfed," said Jay Aldean, a member of Carson City's storm drainage advisory committee.
For that reason, the Lumos and Associates engineering firm hired by City Hall to master plan storm drainage dismissed preliminary notions to contain all water from a 100-year storm with a dam. That would require a dam as high as 55 or 60 feet.
"The height of the dam structure is too great immediately upstream from homes," said Charles Macquarie, the Lumos project manager for the city's Ash and Kings canyons storm drainage detention project.
Instead, Lumos and the Carson City Development Services division plan to deal with storm drainage with a combination of detention basins and large pipes to carry mountain water to the Carson River.
Letting pipes do all the work, however, costs the most.
Late in fall, geotechnical analysis work should start as well as public meetings on how much storm drainage protection people want, said Mahmood Azad, the city's engineering manager.
Azad said public comments will play a large role in the next year in deciding how much the city will pay for storm drainage and whether the system will contain 25-, 50- or 100-year storms. Azad ranks the New Year's Flood of 1997 as a 25-year event.
"The community has to tell me if they're getting sticker shock or not," Azad said.
Aldean, Carson City's former public works director, warned that it is critical to present any storm drainage plan in a way to gain public acceptance.
"Are people out there going to accept a dam?" Aldean asked.
The $31.5 million alternative has no dam. Huge reinforced concrete boxes - pipes - would carry the creeks underground from Ormsby Boulevard to the Lompa Ranch area destined to carry the southern section of the freeway. From there, a separate project would take the water to the Carson River, Macquarie said.
There would be two sets of pipes, both 6-by-8 feet at the upstream end and increasing to 8-by-10 feet downstream. Presently, the streams run through the city in 3- to 4-foot pipes.
The Ash Canyon system would follow the existing channel under Washington Street through Mills Park and Carson High School property. The Kings Canyon system would go under King Street to Division Street or another north-south street before turning onto Fifth Street for the journey to the freeway.
The second alternative calls for a dam and one 60-inch pipe on the Washington Street route to drain the detention basin. This would cost an estimated $9.5 million, Macquarie said.
Lumos and Associates engineers envision a 3,500-foot-long embankment long enough to capture water from both canyons. The dam would go from level at both ends to a peak of 39 feet high and an average height of 22 feet, he said.
"(The price) can go down from there," Azad said. "When you get to value engineering that's where you start hacking at the price."
Value engineering starts after 30 percent of design work is done, not until next year some time.
"I want to leave a very clear picture that we are not proposing this," Azad said. "This is just an idea. We're in very preliminary design. Nothing is set in concrete."
The estimated costs do not include Vicee Canyon, which would add several more million dollars to a flood-control project.
Vicee is more mud threat than the water threat presented by Ash and Kings.
Vicee is not part of the current planning process because the drainage is state and Western Nevada Community College property.