Rick Gunn/Nevada Appeal Two big rigs haul dirt out of the expanded detention basin just south of the WNCC campus Tuesday.
Land managers and Carson City homeowners aren't done worrying about the Waterfall fire just yet.
In fact, "we've got to worry about this for five years," said City Engineer Larry Werner.
That's how long soil experts say it will take new vegetation to take hold, grow roots and anchor the soil on hills scorched by the nearly 9,000-acre Waterfall fire last summer.
Until then, there will still be a fear of mudslides slamming into homes and businesses in Carson City, the way mammoth mudslides covered cars, buildings and people in California this winter.
Along with laying 162,000 pounds of seed and placing more than 1,000 log erosion barriers, and millions of pounds of straw-made filtration devices, Carson City is digging a massive trench near Western Nevada Community College and Vicee Canyon.
The trench is always there to catch sediment as the spring melt-off brings dirt and debris down from the hills. Usually it's enough to hold 15 acre-feet of mud, dirt or water.
By late spring this year, the trench will be a massive hole big enough to hold 150,000 acre-feet. One acre foot is about 326,000 gallons.
Werner said it would take a "five-year-storm" to get some heavy mud-flows moving down the hillside. If mudslides do strike, Werner said, the flows could be up to 15 times greater than a mudslide in a normal year, because of the absence of anchoring vegetation.
There are several areas in Carson City that are at an increased risk of suffering mud-flow damage, Werner said, and it's tough to tell just where a slide will strike.
"It (a mudslide) is not predictable in any shape or form," said University of Nevada, Reno Cooperative Extension educator JoAnne Skelly.
But even if it isn't the only spot where mud might flow, Vicee Canyon is the most critical spot because of the people and buildings near it.
"What we looked at is where the potential for danger is," Werner said.
The basin will cost upwards of $1 million. It would be a lot more, Werner said, if the removed dirt wasn't being used for filler for the Carson City Freeway.
Combined with other projects, land rehabilitation at Vicee Canyon will cost an estimated $2.8 million. Since the Waterfall fire was declared an emergency, federal funds will cover 75 percent of the costs.
In other places, revegetation and erosion control received much of the focus.
Skelly said the wet winter primed the ground for re-seeding and should give rehabilitation efforts a jumpstart.
"It was probably one of the best years I've seen to get the seed down," she said, "but if we have a really dry summer, that will stress it out."
n Contact reporter Cory McConnell at cmcconnell@nevadaappeal.com
