Quick Take:
A couple more storms are heading for Santa Cruz, and they’re expected to bring a substantial amount of rain. That raises further concerns for slides, as the soil is already damp and weakened from earlier rainfall.
Santa Cruz County continues to clean up after high winds, heavy rain and huge waves wreaked havoc around the area this week. The region is also bracing for more storms that experts say come with a serious risk of landslides and debris flows.
Two storm systems are set to hit landfall starting Saturday and continue through Tuesday afternoon. The first is expected to bring up to two inches of rain in Santa Cruz, and up to three-and-a-half inches in the mountains.
The second system — expected to last from Sunday night through Thursday afternoon — is poised to be wetter, bringing three to five inches of rain in most of the Monterey Bay, and as many as nine inches to the highest peaks of the mountains.
“With that much rain, we’re extremely concerned about landslides and debris flow,” said Santa Cruz County Geologist Jeff Nolan. “Mostly in mountainous areas, but there’s also a risk along the coastal bluffs, and any area of steep slopes.”
Flooding is, of course, a big worry, as water levels of local bodies like Soquel Creek and Corralitos Creek have already risen from the last storm. However, it may not be the main point of concern for the coming weather systems.
Nolan added that he is not as worried about the amount of rain as he is with the intensity of the rainfall.
“It can cause flooding at the surface [of the soil] and you get higher water pressure with heavy rainfall, which effectively reduces the strength of the soils, increases their weight, and causes landslides,” he said.
“Areas adjacent to rivers or streams are all at risk of flooding and that can also raise the risk of debris flows, as trees and other objects accumulate in local waterways.
“Anywhere with steep terrain can allow debris to flow down drains and out into the valleys,” said Nolan. “Even if you’re not right at the base of a steep slope, but you are along a stream, you need to have some concern for debris flow.”
The fact that the storms are happening so close together doesn’t do any favors, either. Laura Sullivan-Green, professor and chair of the Department of Civil and Environmental Engineering at San Jose State University, said with the soil so saturated from all the recent rain, the biggest issue in the short-term is whether the water can drain fast enough to prevent flooding.
“If someone’s property has poor drainage, and they have water running across a large swath of it or part of it has been eroded, they can try to divert the water away from the riskiest places.”
Looking forward, Sullivan-Green says, the county can seek to maintain gutters and sewers so that water can drain effectively.
“I wish we had another day or two, but there’s just no time,” she said. “The water levels haven’t even gone down and haven’t crested in a lot of places. RIght now, the best option is to keep sewers clear and tell people if they need to evacuate.”
Sullivan-Green believes that the likelihood of such slides is high, given the wet outlook.
“I think there’s a lot of high potential, but exactly where it may happen or how severely it may happen, we just don’t know,” she said. “We don’t have crystal balls, so the best thing is to remain proactive. Even if something hasn’t happened in these last few storms doesn’t mean that this storm might not be the one that creates the issue.”