Ag Today May 8, 2017

The state of our dams

By Alex Breitler
Record Staff Writer
From their homes, San Joaquin County residents cannot see the dozen-plus large dams that stand between them and a mammoth melting snowpack.

But every day that the lowlands stay dry is a reminder that those dams exist and are doing their job, protecting hundreds of thousands of people and billions of dollars worth of crops and property.

The near-catastrophe at Oroville Dam appears to have shaken the public’s confidence in dams. And not without cause. Most of California’s dams and weirs are at least 60 years old, infrastructure wears down over time, and future storms altered by climate change are expected to test our dams like never before.

Potentially adding to the public’s anxiety, information about the condition of dams that protect us can be difficult to find. Inspection reports and other documents are sometimes withheld by dam owners or operators, who fear that revealing details could compromise security.

Lightly redacted inspection reports obtained by The Record for a few dams upstream of San Joaquin County, along with other documents and interviews, reveal ordinary maintenance issues as well as longer-term, potentially more serious problems.

What they found

Concerns range from minor cracks and trickles of water to, in the case of San Luis Reservoir near Los Banos, the potential for a major earthquake to cause catastrophic failure.

San Joaquin County officials are well aware of this and other threats. And they say the dam operators are, too, as they work closely with the county on regular disaster drills.

“For the dams we’ve been dealing with, they take it pretty seriously,” said Michael Cockrell, head of the county’s Office of Emergency Services. “If they identify a problem and feel they need to get the word out, they know how to do that. That’s one thing we’re pretty comfortable with.”

The Record obtained state Division of Safety of Dams inspection reports for four dams — Pardee, Camanche, Don Pedro and Exchequer. All were judged safe to continue operating.

So was Oroville, in an inspection conducted less than six months before a portion of the main spillway caved in, forcing mass evacuations.

That experience suggests the state’s inspections may not detect potential design flaws in our aging dams, said Bob Bea, a retired professor of civil engineering at the University of California, Berkeley. Bea recently published a preliminary analysis of the Oroville failure.

“(Inspectors) are attempting to reach conclusions based on the standards and guidelines that they’ve been told to use,” Bea said. “But those standards just aren’t appropriate for current conditions.”

A closer look

The dams capable of causing the most damage in San Joaquin County are Camanche, New Hogan and New Melones.

At Camanche, state officials in 2016 noted some water seeping underneath the dam but said it was considered normal. The dam was said to have “no signs of instability or distress.”

An earlier inspection at Camanche, this time by the Federal Energy Regulatory Commission, does highlight some of the inherent risk with an earthen dam. Namely, water could erode the interior of the dam, one of the most common methods of failure.

There’s no evidence that is actually happening at Camanche, the feds concluded, but the potential “cannot be ignored.”

A spokeswoman for the East Bay Municipal Utility District, which owns Camanche and made the documents public, said independent consultants have examined that possibility and consider the risk “very low.” Crews monitor the amount of seepage to ensure there are no problems.

A request for New Hogan inspection records is still pending with the U.S. Army Corps of Engineers, which operates that reservoir east of Stockton during floods. One inherent vulnerability, according to state officials, is that the reservoir behind New Hogan Dam is small and could be overwhelmed during major storms influenced by future climate change.

New Hogan’s Calaveras River watershed is low in elevation and doesn’t receive as much snowmelt. But the watershed does sometimes get hit hard by intense atmospheric river storms, said Michael Mierzwa, a flood management planner for the state Department of Water Resources.

“With increased temperatures, you have increased capacity to hold water in an atmospheric river,” he said. “It’s not just about the transition from snow to rain.”

Other risks

U.S. Bureau of Reclamation officials declined to provide inspection records for New Melones or other federal dams in the region. Todd Hill, the bureau’s regional dam safety coordinator, said officials have not identified significant problems with Melones, which is large enough to accommodate all but the most intense storms.

The bureau is, however, investigating whether much smaller Friant Dam, on the San Joaquin River near Fresno, is at risk of overtopping in future years as snow turns to rain in the High Sierra. After the intense storms this winter, officials mostly drained the reservoir behind Friant to prepare for the coming snowmelt; in the future, that might be more difficult.

No decision has been made on whether action is needed there, Hill said.

A more defined risk exists at San Luis Reservoir near Los Banos. This reservoir is different than the others because it is not on the San Joaquin River or one of its tributaries, and is not filled directly by snowmelt. Rather, it is filled with water that has already drained into the Delta and is then pumped south.

Though not on a river, a dam failure at San Luis could dump water across the Valley into the San Joaquin River all the way to the Delta. Portions of south Stockton could be at risk.

The reservoir was built in the 1960s atop the Ortigalita Fault. Over the years, it became apparent that a major earthquake on the fault could cause the dam to slump, allowing water to gush over the top. That would only happen when the reservoir is relatively full, as it is right now.

The bureau launched a formal study in 2006, but more than a decade later that study isn’t finished and it’s unclear when it will be.

One option is to raise the dam, which would also allow more water to be stored in the reservoir, a key component of California’s massive water projects. Another option is to keep the water level in San Luis low enough that it wouldn’t spill over even if an earthquake damaged the dam.

Deirdre Des Jardins, a consultant for environmental and community groups, says the reservoir should be drawn down now.

“I know there would be less water for crops on the west side of the Valley, and less lawns watered in the southland, but these are people’s lives we’re talking about,” Des Jardins said. “If there was an earthquake and the dam failed, people would say, ‘Everyone knew there was a hazard.’ ”

Reclamation documents indicate the reservoir would have to be kept 50 feet below the top to meet safety guidelines. That would mean substantially less water available to much of the state.

“If you lower the reservoir 50 feet, that’s a massive issue for the water users,” said Todd Hill, the bureau’s regional dam safety coordinator.

Dam failure is “very unlikely” any given year, the bureau says. While the reservoir is close to full right now, it is routinely drawn down in the summer, so the consequences of dam failure would also depend on the time of year.

Hill declined to release the exact probability of dam failure at San Luis, but said Reclamation is “actively working” on the problem.

In the unlikely event …

A few of the major dams perched above San Joaquin County, their condition, and the possible consequences should one fail. Based on inspection reports, emergency planning documents and interviews.

Camanche Dam

  • 171-foot earth- and rock-filled dam built in 1963 on the Mokelumne River.
  • Holds up to 417,000 acre-feet of water.
  • Passed 2016 state inspection. “Normal” seepage; no evidence of internal erosion, which can cause embankment dams to fail, but risk “cannot be ignored.”
  • If it failed: Flood could reach Clements in 24 minutes, east Lodi in two hours, and north Stockton in eight hours. Most of Stockton could flood. Depth could range from a few inches to 15 to 16 feet. Delta islands would likely flood. Hundreds of thousands of people threatened.

New Hogan Dam

  • 210-foot earth- and rock-filled dam built in 1964 on the Calaveras River.
  • Holds up to 317,000 acre-feet of water.
  • Request for inspection report still pending. Future problem may be New Hogan’s small size to handle storms exacerbated by climate change.
  • If it failed: Flood could reach Linden in one hour and 10 minutes and east Stockton in two hours. Most of city could flood. Delta levees could fail. Hundreds of thousands of people threatened.

New Melones Dam

  • 625-foot earth- and rock-filled dam built in 1978 on the Stanislaus River.
  • Holds up to 2.4 million acre-feet of water.
  • Federal officials would not release latest inspection report; said no known major problems. Melones is larger than the other dams and has enough room to capture all but the most intense storms.
  • If it failed: Extensive flooding. Water could reach Escalon in two hours, Ripon in five and one-half hours, Manteca in eight hours and west Stockton in 20 hours. Hundreds of thousands of people threatened.

New Don Pedro Dam

  • 580-foot earth-filled dam built in 1971 on the Tuolumne River.
  • Holds up to 2 million acre-feet of water.
  • Passed 2016 state inspection. Two gates in process of replacement. Reservoir is considered too small to handle inflow from extreme storms, and the amount of water that can be released from dam is limited.
  • If it failed: Could flood Modesto and threaten levees along the San Joaquin River.

New Exchequer Dam

  • 490-foot rock-filled dam built in 1967 on the Merced River.
  • Holds 1 million acre-feet of water.
  • Passed 2016 state inspection. A small area where concrete crumbled due to falling rocks has been repaired.
  • If it failed: Portions of Merced County could flood within hours. Flood would move through western Stanislaus County and into the southern and central Delta, threatening levees.

Friant Dam

  • 319-foot concrete dam built in 1942 on the San Joaquin River.
  • Holds up to 520,500 acre-feet of water.
  • Federal officials would not release an inspection report. Friant is believed to be too small to handle intense future storms in which some Sierra Nevada snow falls instead as rain.
  • Water would flood hundreds of square miles in Fresno, Madera and Merced counties; water would eventually flow to Delta.

B.F. Sisk Dam (San Luis Reservoir)

  • 300-foot earthen dam built in 1967 to store water pumped south from the Delta.
  • Holds up to 2 million acre-feet of water.
  • Federal officials would not release latest inspection report. Reservoir was built over earthquake fault. When reservoir is almost full, as it is now, an earthquake could cause the dam to slump and water to pour over the top.
  • If it failed: Could threaten Los Banos. Could flood west Manteca within 30 hours and west Stockton within 60 hours.