Water Worries

Officials said Wednesday Success Dam is safe despite an increasing water level due to recent storms.

Calvin Foster, operations area manager for the Sacramento District Corps of Engineers at the lake, said he and his engineers are “mitigating any risk” and will continue to do so as more rain is expected.

“Public safety is our number one concern,” he said.

As of 3 p.m. Wednesday, the lake was holding 39,516 acre feet of water at a pool elevation of 628.96 feet. It had risen 2.29 feet since 7 a.m. Wednesday, according to hourly reports posted online. Before the storms hit Dec. 17, the lake had less than 13,000 acre feet of water.

The lake is a flood control reservoir. Thus, the water level must be drawn down to leave room for runoff. Because of earthquake concerns, lake officials have tried to keep storage below 40,000 acre feet.

The lake is considered full at 82,000 acre feet, or 652.5 feet elevation, and rose 24 feet from Dec. 17 to 21 alone, Foster said. It has a pool restriction of 630 feet elevation.

“We feel good about what we’re doing,” Foster said in terms of monitoring the situation.
Two inflow sources — the Globe and South Fork monitoring stations — pour into the lake.
As of 3 p.m. Wednesday, both sources combined to produce inflows of 4,231 cubic feet per second. On Dec. 19, inflows were measured at 22,000 cfs, Foster said. Inflows between 1,500 cfs and 6,000 cfs, depending on storm events, are about average, he said.
The dam, which is a rolled-earth structure with a clay core, is of primary concern.
As of 3 p.m. Wednesday, water was rushing through the outlet at 819 second feet.
“With the inflows right now, we’ll probably see that number increase,” Foster said.
Officials say the river below the dam can handle a release up to 3,200 second feet.
Late Wednesday, Foster said he expected the lake’s elevation to reach somewhere between 632 and 633 feet.
“If we get to 630 feet elevation,” Foster said, “I would expect to see an increase in the outflow.”

The dam is experiencing some common seepage issues, Foster said. The possibility of an earthquake, which could cause cracking in the dam, is the “main driver for risk,” he said.

The dam was built in 1961 and sits on a layer of recent alluvium, or stream deposit. An 8.0-magnitude earthquake on the San Andreas Fault could cause the alluvium to liquefy and the dam to settle, potentially leading to cracking problems in the dam, Foster said.

“We’re in that cycle right now of extra monitoring,” he said. “The guys are well trained.”
Success Lake watermaster Dan Vink, of the Lower Tule Irrigation District, said the channel capacity of the Tule River through Porterville can handle about 3,000 cfs. Through the Woodville area, as the channel gets smaller, capacity drops to about 2,000 cfs.

“We have no intention of getting that high,” Vink said.

Lake officials cannot begin to fill the reservoir until the end of February.