OGDEN — Raise your hand if your vehicle’s ever sustained rock damage in Ogden Canyon.
A report commissioned after a plunging boulder critically injured a driver at Pineview Dam in December has identified 13 high-hazard rockfall zones in the canyon that may deserve prevention work.
A 150-pound boulder crashed through a pickup's windshield on State Road 158 on Dec. 15, 2018. The 57-year-old Layton driver survived what authorities termed a rare incident.
The incident resulted in a geotechnical study by the Utah Department of Transportation to gauge the hazard there and recommend possible mitigation projects.
Installing rockfall mesh drapery and realigning the road five feet to the south would eliminate the danger on most of the dangerous section and would cost $1.1 million, the report says.
But the report, obtained with a public records request, suggests a closer look be given to greater dangers close by.
"Any evaluation of rockfall hazard at SR 158 near Pineview Dam should consider several nearby sites with similar or even higher associated rockfall hazards," the report said.
UDOT’s rockfall risk database, developed by Utah State University, includes about 1,100 sites statewide.
Starting with the Pineview site, there are 13 high-hazard sites on the seven-mile stretch between the dam and west to the mouth of Ogden Canyon, according to the geotechnical report.
The Pineview site has the lowest hazard rating of the 13, primarily because the rocks there tend to be small and drivers can see them soon enough to avoid them, the report says.
That’s not the case in the winding canyon, where sight lines are much more restricted.
Ratings are given for low, moderate or high potential for rockfall to reach the roadway. About 500 sites have a moderate or high hazard rating.
Hazard scores range from 0 to 2,584 based on an algorithm that considers road and ditch geometry, geologic conditions, rockfall history and traffic data.
The hazard calculation reflects both the potential for rocks to reach the roadway and the damage that can result. Areas with blind curves, narrow catchment ditches and high traffic volumes tend to have higher hazard ratings.
Of the moderate or high hazard sites, 47 percent scored less than 25 on the risk scale. Just 6 percent (33 sites) scored greater than 400. Four of those sites are in Ogden Canyon.
Regardless whether the Pineview project is undertaken, “it is possible that the next serious incident will occur at another site,” the report says.
“It may be feasible to use rockfall drapery to mitigate the three rockfall sites with the highest hazard scores in Ogden Canyon, at mileposts 11.8, 12.1 and 12.8,” according to the report, because they are smaller than the rockfall-prone north face above the Pineview road.
Those three sites could be made safer for about half the cost of the proposed Pineview mitigation, the report says.
Other steps to hinder rockfall could include construction of barrier fences and rock excavation.
At the Pineview site, the underlying causes of abundant loose rock and an undersized catchment ditch — which is intended to capture rocks before they get to the road — remain.
“It is very difficult to quantify the risk of something similar happening in the future,” the report said, but “as traffic volumes on this road increase, so will the risk.”
A rockfall mesh drapery would be suspended at the top of the slope from horizontal cables. The drapery holds loose rocks in place and prevents bouncing so rocks don’t reach the road, according to the report.
UDOT Region 1 spokesman Vic Saunders said the agency, for now, will make sure enough falling-rocks signs are placed and will continue to patrol the roads daily to pick up the geologic debris.
Any further action will depend on budget priorities and continued evaluation of the risks posed by the identified hazard sites.
If the potential danger is significant enough, “it is something we have to act on right away,” Saunders said. “Something that happened only one time — how much do you spend for something that may not happen at all?”
The Dec. 15 boulder strike was described as a very unusual and perhaps unprecedented event in Region 1.
A mitigation proposal would have to go up against other projects planned in the region, he added.
Another complication: A lot of the risky rock zones are on federal or private land, Saunders said. UDOT has an easement for the roads but does not own all of the land.
“We always say safety is job one,” Saunders said. “We want (drivers) to be safe and we do the things that are reasonable to allow that safety to occur. We can’t prevent everything, but we can make a good effort to prevent what we can.”
Weber County Commissioner Gage Froerer, who lives in the Ogden Valley and estimates he’s been driving on the two state roads for five decades, said Thursday he hopes to work this spring with his fellow commissioners, UDOT, and state Rep. Steve Waldrip to investigate possible solutions.
There might be a public hearing so people who use the road can weigh in, he said.
“Bottom line, there are no easy answers,” Froerer said.
While there’s no budget for improvements now, Froerer said he would be willing to work with UDOT and lawmakers to seek state funds later if an effective project is decided upon.
“Anything you do is going to have some type of repercussions,” he said, adding that mountainsides may be disrupted by the work, and a giant metal drapery could be aesthetically objectionable.
The geotechnical team reviewed Weber County Sheriff’s Office traffic incident records as part of its study. It found there were 28 vehicle damage incidents from falling rocks over the past three years at the Pineview site.
The reports likely underestimate the actual volume because many incidents probably are not reported to authorities, the report says.