Rainfall brings mudslides FIRST OF SEVERAL STORMS
Pier Fire burn area closed to all but local traffic
Ever since the Pier Fire that burned over 33,000 acres last August between Springville and Camp Nelson was fully contained and extinguished, local agencies have said it was not a matter of if, but when the area charred by the blaze would also experience mudslides.
That “when” turned out to be Tuesday night, when a section of Highway 190 seven miles east of Springville was closed at around 8:30 p.m. by Caltrans to all but local traffic as mudslides completely covered the roadway.
The slide was triggered by a period of heavy rainfall in Tuesday’s storm— the first of several to move through Central California this week.
Christian Lukens, acting chief of public information for Caltrans District 6, said maintenance crews worked through the night to clear debris and make the road passable.
A Caltrans maintenance supervisor present at the mudslide site said he has seen what winter weather events can do to roadways in past years, but he hasn’t seen anything like Tuesday’s slide in quite a while, and that the Pier Fire definitely played a role.
“Any time you have that level of burnover it’s not just the lack of vegetation, it also scorches the soil, which makes it hard for the soil to absorb the water,” said Jerald Meadows, warning coordination meteorologist for the National Weather Service in Hanford.
Highway 190 was reopened at approximately 8:30 a.m. Wednesday morning for all traffic. Front end loaders and a backhoe remained at the site after it re-opened to clean up, but were entirely clear of the highway.
The location of the slide — Highway 190 milepost 39.9 near the Wishon Road turnoff and the PG&E Tule River powerhouse— is one of the spots along the windy mountain road U.S. Forest District Ranger Eric Laprice pointed to as likely candidates for mudslide or erosion at a town hall meeting in Springville last November addressing the effects of the Pier Fire on local travel and safety. He also identified spots on the highway below Pierpoint Springs, Soda Creek, and Moorehouse Creek as problematic.
“[These areas] have the highest probabilities of being our points that cause the entire highway to be closed,” said Laprice at the November meeting.
Although the mudslide closed the highway for twelve hours, the storm system that caused it has so far delivered far less rainfall than expected, meaning the results could have been far worse.
Meadows said in such scenarios, however, it is less about total rainfall amounts and more about rainfall rates.
“Tuesday [the area of the mudslide] received about half an inch of rain in 30 minutes, which gets us to a rate of an inch an hour — a pretty substantial rainfall rate for our area,” said Meadows.
He added that even normal soil and terrain will experience runoff of small rocks and debris at that rainfall rate, simply because there is so much water in so little time.
The lack of vegetation and scorched soil in the Pier Fire burn area further hinder the terrain’s capability to sop up the rainfall.
“It’s like dumping a bucket of water on the ground. Most of it will pool up or spill over long before it can soak into the soil,” said Meadows.
The storm that meteorologists and residents alike were hoping would bring up to an inch of rain on the Valley floor by Wednesday evening ended up delivering far less — about .10 inch.
The next storm system is still scheduled to arrive late Thursday evening and last through Friday, followed by a smaller one on the weekend. The NWS outlook for mudslide hazards with those storms is one of cautious optimism.
“At this time I’m not expecting any of the rainfall rates we saw Tuesday, specifically in the Pier Fire area, but it is always a possibility, especially with thunderstorms, which we have slight potential for Thursday,” said Meadows. “But I will add that any time the soils are already saturated and things have already mobilized, sometimes they can be susceptible to mudslides again, and we will have a prolonged rain event and high elevation snow through the end of the week.”
Regardless of the conditions the upcoming storms produce, Caltrans will be paying close attention as the week progresses.
“Our maintenance crews are on standby regardless, 24/7, 365 days a year,” said Lukens. “It’s something they can be called upon for at any hour of the day or night.”