Napa County next year could take a high-profile, $2.5 million step in its disaster recovery road repair efforts by finally taming the Silverado Trail slide.
A triple whammy of storms, fire and earthquake in recent years took their toll on the rural road system. The storm damage at Silverado Trail stands out because this is a major north-south Napa Valley roadway handling more than 10,000 trips daily.
The storms of January 2017 caused volcanic boulders the size of a Volkswagens to fall onto Silverado Trail near Pratt Avenue north of St. Helena. The county had to remove dozens of truckloads of debris to keep the road open.
Ever since then, a short section of road has been narrowed to make room for an 8-foot-tall, steel-and-concrete wall that protects drivers from further slides. The Pratt Avenue entrance to the road has been closed because of this jury-rigged safety measure.
The permanent Silverado solution is at hand.
“We’re designing a fix that will stabilize that slide,” county Public Works Director Steven Lederer said.
He stepped to a white board and sketched out the situation. The hill along the road has the bottom 50 feet or so carved away by slides, making the soils above unstable.
The idea is to fill this gap with rock, basically creating a stronger, stable version of the hillside. A small fence or netting could be added for extra protection from small, rolling debris.
Work could begin next spring and the project could be done next summer, Lederer said. Then the concrete wall would be removed and Silverado Trail would be a normal width, with the Pratt Avenue connection restored.
The narrowness of Silverado Trail at the wall hasn’t created an accident hot spot, according to Lederer. But, he said, it is inconvenient for cyclists.
When the Silverado Trail slide stabilization work is done, Lederer will be able to tick off one more item from the county’s long disaster road-repair list.
The storms damaged about 40 road sites to varying degrees, county officials announced in their wake. From Mount Veeder to Wooden Valley to Pope Valley to Lake Berryessa, rain-triggered slides left their mark on rural pavement.
Last year, the county began work on six storm-related projects at a cost of $9.5 million. A new county roads list shows 22 major storm repair projects remaining to be done over three years at an estimated cost of about $19 million.
Several Mount Veeder residents went to the Sept. 11 Board of Supervisors meeting to talk roads. They said narrow Mount Veeder Road was bad before the 2017 storms and worse afterward, with two areas that go down to one lane because of slides.
“Our road is our lifeline, our safety,” Vicky Van Dewark said. “Our property values are all being threatened.”
In the wake of the October wildfires, cement trucks are coming up the road to help with rebuilding, Van Dewark said. Logging trucks are coming up.
“We need our road fixed,” she said.
The October wildfires didn’t ruin road pavement, but created its own set of road issues. The 2018-19 county budget released last spring mentions replacing about a mile of fire-damaged guardrails and removing 340 fire-damaged trees, in addition to repair work already done.
Some road damage from the 2014 South Napa earthquake remains to be fixed. The 2018-19 budget mentioned 23 remaining projects.
Among them is replacing the damaged bridge on rural Partrick Road in the southernmost Mayacamas Mountains about a mile outside of Napa city limits. The county in November 2014 slipped a steel, military-style Bailey bridge over the top to shore the structure up until it can build a new bridge.
The county is still pursing Federal Emergency Management Agency money to replace the Partrick Road bridge, Lederer said. The bridge replacement cost is listed as $2 million on the county’s roads list.