Marin Municipal Water District seeks grant to study reservoir expansion

The Marin Municipal Water District is seeking nearly $662,000 in federal funding to study the potential of increasing water storage at its three largest reservoirs.

The district has not added or expanded reservoirs since the early 1980s. After the drought of 2020-2021 threatened to deplete local reservoirs, the agency decided to explore the option as part of a recently adopted roadmap to expand its water supplies.

The district board voted unanimously on Tuesday to approve the application for the grant from the U.S. Bureau of Reclamation.

“Understanding our ability to increase storage is part of the integrated roadmap that we approved,” board member Ranjiv Khush said before the vote. “It seems like moving forward with this is in alignment with our strategy.”

Board member Matt Samson said that while some might view the action as yet another study, he said this type of work is needed for projects of this significance that would affect future generations.

“We have to be able to get this right because we don’t really get to have it wrong,” Samson said. “This not only helps us do that but it also helps with the financial piece so that we can look at funds for other items.”

If awarded later this fall, the grant would pay to study the potential benefits and effects of increased water storage at the district’s Kent, Nicasio and Soulajule reservoirs, said district grants coordinator Matt Sagues. The studies would include modeling how increasing storage capacity could affect streamflows, performing geotechnical investigations of the three dams and expanding the district’s existing fish monitoring technology.

The district’s water supply roadmap adopted last month estimated that raising the dam or adding a moveable spillway gate at one of the three reservoirs could provide an additional 5,000 acre-feet of water each year. The district’s seven reservoirs can hold about 80,000 acre-feet of water, which is about a two-year water supply. Raising the dam or installing a moveable spillway gate at one of these reservoirs is estimated to cost up to $90 million.

Should the district be get the federal grant, it would need to provide about $729,000 in matching contributions, including staff time, Sagues said.

“That is a huge investment,” board member Jed Smith said during the meeting. “That’s more than the entire water supply roadmap study that Jacobs (Engineering) just did. So this is not insignificant.”

Monty Schmitt, the board president, said that along with the large financial commitment, the possibility of expanding reservoir storage will likely trigger a review of the district’s state water rights.

“That is a foundational issue that we need to understand better before we embark on a $700,000-plus investment,” Schmitt said.

The last time the district explored the idea of increasing reservoir storage occurred after the 1976-77 drought, which nearly depleted local reservoirs for most of the county. The crisis was averted through the construction of an emergency water pipeline across the Richmond-San Rafael Bridge and a wet winter in 1977-78.

Following the drought, residents who were once wary of increasing local supplies because of fears of too much community growth changed their minds. That eventually led to the creation of the Soulajule Reservoir in 1980, which is now the district’s third-largest reservoir, and a project that doubled the capacity of Kent Lake in 1983. No reservoir expansion projects have occurred since then.

The drought in 2020-21 threatened to deplete local reservoir supplies as soon as mid-2022. As it did in 1976-77, the district explored building a pipeline across the bridge, but the plan was shelved after heavy downpours nearly refilled reservoirs by the start of 2022.

Instead, the district began a study of new water supplies, which resulted in the water supply roadmap adopted in March.

Other projects being considered by the district include a potential brackish desalination plan on the Petaluma River; enhancing conservation programs; importing more Russian River water; creating a regional groundwater bank in Sonoma County; and creating new connections between existing reservoirs.