Sinkholes In Santa Rosa Burn Area Are City's Newest Concern

SONOMA COUNTY, CA — Residents of parts of the hilly Fountaingrove area of Santa Rosa were advised Sunday afternoon that they should be ready to evacuate because forecasted rain may result in flooding, landslides and sinkholes. Santa Rosa city officials gathered with residents Sunday afternoon at the Finley Community Center at 2060 W. College Ave. to tell them that the wildfires last month destroyed some storm drainpipes leaving voids underground and causing at least one sinkhole.

The officials said pipes at eight other locations burned, which could prompt more sinkholes as well as landslides and flooding during the coming storms.

Crews are investigating 20 other sites where pipes may have been affected by fire.

"The pipes caught fire and in some cases were destroyed for significant lengths of up to a few hundred feet," Bennett Horenstein, director of Santa Rosa Water, said.

The first sinkhole was discovered Friday at the end of Newbury Court and had been repaired as of this evening, Adriane Mertens, a spokeswoman for the Santa Rosa Emergency Operations Center, said.

The sinkhole occurred when 250 feet of pipe was destroyed, causing a 4-foot diameter, 7-foot deep hole.

City officials have reopened the emergency operations center because of the potential for more damage and evacuations.

City crews will be monitoring the Fountaingrove area until they have identified and repaired all the damaged infrastructure.

Six sections of the Fountaingrove neighborhood are at risk. The identified areas have as few as 78 residents and as many as 200.

City officials on Sunday provided a damage assessment map.

City crews are using television cameras, among other means, to identify the drainpipes that have burned.

"We have 10 strike teams with CCTV cameras that run into the entire length of the pipe assessing the suspect areas," officials said. "We also have six teams of engineers and geologists that are assessing each confirmed site to determine the risks. ... Each site is unique. It depends on the length of pipe that was made out of plastic. There could be a short section with minimal risk or a much longer reach of pipe with more risk."

Thus far, the problem is primarily in Fountaingrove, officials explained, because of the type of pipe — high density polyethylene, or HDPE — used when Fountaingrove was developed. HDPE wasn't used until about 20 years ago, and Fountaingrove is a newer development than Coffey Park.

"The Coffey Park area is older, and also the risk if there was a pipe there is much less because it’s flat and the pipes are much shallower," officials said. "In Fountaingrove there’s more risk if we have a collapse because the pipes are deeper and there’s more hillside exposure."

Light rain was expected overnight in Santa Rosa, Jim Wallmann of the National Weather Service said Sunday. Heavier rain will fall between 9 a.m. and 2 p.m. Monday. The storm could bring as much as an inch of rain to the hills. Up to a half an inch could fall in the valleys, Wallmann said.

The forecast calls for winds of 10 to 15 mph with gusts of up to 25 mph.

Tuesday is expected to be dry but rain is forecast to fall again Wednesday and Wednesday night. Up to three-quarters of an inch is expected in the valleys and up to an inch and a half in the hills.

The heaviest rain will fall Wednesday afternoon into Wednesday evening, according to Wallmann.

Anyone who sees evidence of flooding, mud and debris flows or sinkholes should call 911, city of Santa Rosa and county of Sonoma officials said.

Regarding the rainfall last week in the area, city officials said they didn't see any significant issues but it may have revealed the sinkhole, helping them understand the scope of the issue.

Bay City News Service contributed to this report.

Image via City of Santa Rosa