Flood threat: Boils appear on Tuolumne and San Joaquin river levees in Stanislaus County

Crews from Stanislaus County and the state are dealing with boils on river levees, as the threat of river flooding intensifies.

Tuesday afternoon, county Public Works crews and the state Department of Water Resources were working to repair a boil on the San Joaquin River near Patterson, said Deputy Raj Singh, a spokesman for the county Office of Emergency Services.

The boil was discovered Tuesday morning near the old fishing access at Poplar Avenue and Old Las Palmas Avenue, not far from the Las Palmas Avenue bridge over the San Joaquin.

Monday night, workers from the county and state patched up a boil on the Tuolumne River near Shiloh Road west of Modesto. The crews were able to shore up the weak spot on the levee without further issues, Singh said.

Boils occur when long-term high water levels exert a strain on river levees. As the water places intense pressure on the soil underneath the levee, it may seep through a weak spot and threaten the structural integrity of the flood control berm.

Two crews from the California Conservation Corps were filling and prepping sandbags to take them to the repair operation near Patterson. The area on the west side of the river is under an evacuation warning.

“These boils are concerning,” Singh said, noting that local districts and farmers have been patrolling the levees around the clock to watch for boils or other problems.

The river near Patterson is projected to rise to 50.8 feet by Wednesday afternoon, which is about four feet below the apparent flood stage. But it’s also near an historic high for that stretch of river. And the boil is a sign of potential flooding.

The high-running Tuolumne and San Joaquin rivers are posing a flood danger from Modesto and Newman to the south San Joaquin County cities of Manteca and Lathrop.

Stanislaus residents weathered another rain and wind storm Tuesday, which brought a third of an inch of rain to Modesto by noon, followed by a thunderstorm and hail late afternoon.

Singh said the San Joaquin River level near Patterson is forecast to remain high for at least another five days.