Marin water district tests supply options against severe drought

The Marin Municipal Water District plans to consider recommended new supply options beginning in February.

As the Marin Municipal Water District nears the end of a yearlong study into new water supplies, its governing board took a deeper dive this month into how well different portfolios of options could help prevent severe water shortages in a worst-case scenario drought.

“We’re at the point now where it’s all starting to come together,” district official Paul Sellier told the board this week.

The study, which began in early 2022, is examining a variety of new water supplies, including interties with other water agencies, desalination, expanding conservation programs, groundwater storage, maximizing Sonoma County water imports, enlarging storage capacity of local reservoirs and recycled water expansion.

The effort was launched after the district and the 191,000 central and southern Marin residents it serves faced depleting local reservoir supplies as soon as mid-2022 after a severe two-year drought.

Rains in late 2021 worked to nearly refill local reservoirs but demonstrated the vulnerability of the local water supply. Voters responded in 2022 by electing three new board members — Ranjiv Khush, Matthew Samson and Jed Smith — who had campaigned on bolstering local supplies.

On Tuesday, the district board and its consultants from Jacobs Engineering reviewed how well four portfolios of water supply options performed against a severe four-year drought. The simulated drought combined the district’s two worst droughts of record in 2020-2021 and 1976-1977. The portfolios include:

• Maximize local and regional water supplies. Includes expanding water imports from Sonoma County, enlarging reservoirs, expanding reservoir capacity.
• New local supplies. Includes desalination plants, expansion of recycled water system.
• Diversifying water imports. Interties with outside water agencies, including building a pipeline across the Richmond-San Rafael Bridge to pump in Central Valley water.
• Low-cost options. Includes options that cost less than $2,250 per acre-foot of water produced. Includes conservation program expansion, a brackish desalination plant on the Petaluma River, groundwater banking, adding adjustable gates to reservoir spillways.

The district does not intend to pick one portfolio of options but rather a variety of options from each based on criteria such as water yield, cost, environmental impacts, regulatory hurdles, public acceptance and other factors.

“We can mix and match to help put together a portfolio that we think would work in the short, medium and long term,” Smith said during the meeting.

The district plans to review potential combinations of supply options it could choose in February before deciding on what options to pursue at a later date.

The simulation results presented on Tuesday showed how well these portfolios prevented the district from dipping below emergency storage levels and whether it would be able to meet customer water demand during this four-year drought.

The district’s seven reservoirs hold about 80,000 acre-feet of water, which is about a two-year water supply. When water levels dip below 30,000 acre-feet, the district considers this to be emergency storage.

Each portfolio was passed through the drought simulation to calculate how much storage levels dipped below 30,000 acre-feet and whether there would be a resulting shortage of water to meet customer demand based on factors such as certain reservoirs going dry or state-mandated dam releases for fish. To compare each portfolio’s performance, the district combined both the supply and demand shortage volumes for each and divided them over the four years to come up with an annual average deficit.

Of the four portfolios, the water imports portfolio had the largest deficit of water during this simulation of about 3,700 acre-feet per year, with an acre-foot being about 326,000 gallons. Maximizing local supplies only showed a 300-acre-foot shortage by comparison while the low-cost and new local supplies options avoided a deficit altogether.

District consultant Armin Munevar said avoiding these shortages would take several years to achieve, with the district beginning with initiatives such as conservation enhancement while it plans for larger projects such as enlarging reservoirs or desalination, for example.

“Take home here is a number of these more long-term, fully developed pathways provide sufficient yield and reliability to resolve the challenges,” Munevar told the board.

Additionally, Munevar said water conservation will be integral to whether these new water supplies prevent deficits.

“Conservation and drought restrictions are key elements that have to be on the table and in my view are no-regret, low-regret options,” he said.

The findings prompted a discussion among board members on whether they should forgo further study of water interties to the East Bay or San Francisco altogether given their performance in the simulation. Samson and board president Monty Schmitt voiced support for narrowing the scope of options away from interties, given the findings, as well as the major construction and regulatory hurdles associated with these projects.

“We have to start narrowing our view as we start to look at other options,” Samson said.

“If we’re going down an intertie pathway, there is a very substantial all-or-nothing commitment,” Schmitt said.

Khush and board member Larry Russell urged the district to wait until the final study report is released before making any decisions, which the board ultimately opted to do.

While options such as enlarging reservoirs or adding spillway gates to dams provided supply benefits, Schmitt also raised concerns about how many options rely on augmenting local storage, especially given the regulatory hurdles. Expanding reservoir storage could trigger potential changes to the district’s state water rights, which could set in motion a lengthy review process. One outcome that board members previously expressed concern over is whether the state would require the added water to be used for environmental releases rather than human use.

Former district board member Larry Bragman of Fairfax urged the board to begin at least exploring these options, such as raising the heights of spillways or spillway gates.

He said the neighboring North Marin Water District has had preliminary talks with the state without much pushback for its proposal to add a spillway gate to its Stafford Lake reservoir near Novato.

“I really think we should get moving on that and put some exploratory lines of communication out to let them know what we’re thinking about,” he said.