Marin grand jury: Water utilities should fortify dam safety plans

Following the barrage of drenching storms this winter, Marin County’s dam safety plans are failing to account for more frequent, intense storms brought on by climate change, according a new report.

While the report by the Marin County Civil Grand Jury says the eight dams operated by the Marin Municipal Water District and the North Marin Water District are in full compliance with state and federal safety standards, the agencies’ dam hazard plans do not incorporate the latest science on climate change effects on “atmospheric river” storms.

“Of note, no failures took place thus far, in part because water levels in dams were low due to the prolonged drought,” the report states. “However, with stronger atmospheric rivers happening in greater numbers, and perhaps higher water levels in the dams, the situation could be different.”

The grand jury recommends, among other actions, that the two water districts update their dam hazard mitigation plans and form a committee to plan strategies to prevent potential dam failures.

Both utilities are required by the state Division of Safety of Dams to submit hazard mitigation plans. However, the grand jury says the state and federal governments do not require dam operators to employ specific methodologies or actions to address dam safety, instead leaving it up to the operators themselves to determine which approaches work best for their dams.

The report notes that the average age of Marin County’s eight large dams is 87 years, with the oldest dam, at Lake Lagunitas, dating back to 1872. The state has classified all these dams as having the highest safety rating of “satisfactory.”

The Federal Emergency Management Agency has a separate hazard classification based on the potential impacts downstream if a dam fails. Seven dams — Alpine, Bon Tempe, Peters at Kent Lake, Seeger at the Nicasio Reservoir, Stafford, Phoenix and Soulajule — are classified at the highest risk hazard catregory, meaning that a dam failure would likely cause loss of human lives, according to the report.

Lagunitas Dam is classified as having “significant” risk, meaning it would likely cause property and environmental damages resulting in economic losses.

The communities that face the greatest risks are Novato, Point Reyes Station and Ross, which are downstream of these dams and comprise about 20% of the county population, the grand jury states.

Projections that climate change will result in more extreme swings in weather — from prolonged droughts to more extreme rainfall — should be “front and center” in the water district’s dam safety plans, the report states.

“Construction standards have changed considerably over the years and older dams usually do not have good construction records,” the report says. “The Grand Jury finds the issue of dam safety is relevant in light of climate change and increasing strength and number of atmospheric rivers. This now requires a critical review to proactively mitigate future potential hazards.”

Leaders from both water agencies said they are aware of the projections for more extreme weather patterns. They said they have no concerns about the structural safety of the dams currently, and that the utilities perform daily checkups along with more intensive inspections throughout the year.

“At this point, we haven’t had any concerns about it because not only do we have the spillway, but we have outlet valves to release water quicker,” said Crystal Yezman, a Marin Municipal Water District engineer. “The biggest concern there is the spillway is undersized and we haven’t had anything like that.”

The district operates seven of the eight large dams in Marin. Six are earthen dams, and Alpine Dam is concrete. Yezman said the dams are regularly inspected, including after major storms. The agency’s dam safety plan was last updated in 2020. Another is forthcoming to add in water supply projects the district is pursuing, Yezman said.

Agency staff declined to comment on the grand jury recommendations, stating that the district’s board will decide how to respond.

The district plans to make a presentation at the board’s July 21 operations committee meeting about its dam safety programs.

The North Marin Water District operates the earthen dam at Stafford Lake just outside of Novato. Unlike its neighboring water agency, the district’s dam safety plan is incorporated into the countywide hazard mitigation plan, which is being updated.

Tony Williams, the district’s general manager, said there will be discussions on climate change and other hazards during the update process, but he said the district has “never had any concerns thus far” about the safety of Stafford Dam.

Williams said the grand jury report seems to be critical of state and federal regulatory agencies for being too slow or not responding to the latest climate change projections, and that local water agencies should take a proactive approach to incorporate this.

No guidance exists on the issue from these larger agencies that have a staff of specialists looking into the issue, Williams said. By comparison, Williams said the water district has three civil engineers on staff, including himself.

“We acknowledge that is an issue,” Williams said of the grand jury’s concerns. “The question is, are we the ones that should be figuring out how to apply that science to the right engineering criteria for a dam? That’s what those agencies are tasked with doing.”

Williams said the report also contains some factual errors, including that his district owns the dam at Nicasio Reservoir and that the federal dam hazard classifications are based on the potential for dam failure, as opposed to the downstream impacts should a dam fail.

The Marin County Civil Grand Jury is a panel of volunteers empowered by the local judiciary to investigate the workings of public agencies. A copy of the grand jury report can be found at marincounty.org/depts/gj.