Sheila Kirton, a Caltrans construction site inspector and engineer, Thursday stood on Highway 26 in Calaveras County next to a 25-foot-high eroded slope of unstable red dirt looming above snow-speckled frozen mud, rocks and boulders crowding the narrow mountain watershed roadway.
“We had four inches of rain in an hour up here a week ago,” Kirton said. “That brought down tons of material on the road, and undermined paved roadway surfaces on the downhill side.”
Kirton was talking about what Caltrans District 10 staff are calling the “Valentine’s Day Deluge” that swamped Calaveras County on Feb. 14. A line of heavy thunderstorms laden with moisture marched across west Tuolumne County and into central Calaveras County and dumped intense rains for several hours, said Idamis Del Valle with the National Weather Service.
A 2.5-mile-long section of Highway 26 is closed about 10 miles east of Mokelumne Hill until at least early March for emergency assessments and repairs, and geotechnical engineers were out there Thursday trying to figure out what steps need to be taken to make the road safe for the public again.
“It looks like two to three weeks for the hard closure, to stabilize slopes and make it safe enough to open one lane,” Warren Alford, a Caltrans District 10 public information officer, said shortly after 1 p.m. Thursday at the west end of the closure at Deardorff Road about 2.5 miles east of Glencoe. “We want to get it open for one-way traffic controls as soon as possible. We don’t know how long one-way traffic controls will be necessary.”
All timetables for completing the project and reopening the road are contingent on weather. It’s been snowing on workers on the Highway 26 closures almost every day this week, Alford said. Another heavy rainstorm could cause even more problems. Slow-moving atmospheric river storms like the one that pounded the Mother Lode are capable of dumping enormous amounts of rainfall in short periods of time.
The east end of the closure on Highway 26 is Woodhouse Mine Road. The section of road that is closed includes the Highway 26 bridge over the South Fork Mokelumne River.
Issues the Caltrans engineers are trying to deal with include steep, destabilized slopes on the uphill sides of Highway 26, blocked drainage culverts intended to carry runoff under the road, and undermined road surfaces and supporting slopes on downhill sides of the road.
The area most hard-hit on Highway 26 is not within the 110-square-mile 2015 Butte Fire scar, Kirton said. Postfire erosion was not a factor in the damage to Highway 26. Rainfall intensities approaching 4 inches per hour were enough by themselves to loosen and mobilize tons of mud, rocks and trees during the Valentine’s Day storm. The roadway on the closed section of Highway 26 was severely eroded due to the massive amount of water from the storm event Feb. 14 and must be fully repaired before re-opening, Alford said.
Kirton stood next to one section of Highway 26 where a lip of exposed paved road surface is now undermined and resting on thin air, emphasizing the road is not safe for the public. She pointed at plastic pipes below and said they are exposed Volcano Communications conduit lines that carry phone, fiber optic and internet service to local residents. The lines are undamaged and still providing service, but work must be done to secure and stabilize those lines, Kirton said.
The closure on Highway 26 is expected to be long-term in order to repair damage from multiple washouts that damaged the roadway, Alford said. An estimated date of completion for repairs and restoration work has not been determined.
Caltrans Distrtict 10 crews have cleared some drains and made some repairs at multiple locations on Highway, while other crews continue keeping constant watch on other state roads in Calaveras and Tuolumne counties impacted by last week’s storm, Alford said. Highway 26 is just one of the problem area Caltrans District 10 crews are dealing with.
More storms are on the way this weekend, but forecasters say primary storm impacts will be north of Interstate 80 and the Mother Lode. There’s potential for more warmer rainstorms Monday, Tuesday and Wednesday next week in Calaveras and Tuolumne counties, as well as Friday and Saturday next week.
Contact Guy McCarthy at firstname.lastname@example.org or 588-4585. Follow him on Twitter at @GuyMcCarthy.