Where will California North Coast get its water if drought becomes common?

With parts of the North Coast facing what forecasters say is shaping up to be “extreme drought” this year, the region’s water managers are busy exploring near- and long-term options.

But new large reservoirs like Lake Sonoma and Lake Mendocino aren’t among them.

Even as the first of seven large reservoirs funded by the 2014 $2.7 billion California water bond is set to get under construction elsewhere in the state, agency officials and local lawmakers say the regulatory and political environment has shifted dramatically from decades ago when the Golden State’s big water catchments were constructed.

Beyond eking out capacity in the region’s existing reservoirs, the long-term answer for increasing water supply in the most stressed areas, they say, likely will be below ground, rather than above.

“We’re not going to see another large reservoir in the North Bay. That’s not going to happen,” said Assemblymember Jim Wood, D-Santa Rosa, whose North Coast district stretches from north Santa Rosa to the Oregon border.

The reason, according to Wood and other legislators and officials, is that the dam-building spree that led to the construction of thousands of dams in Western states in the first half of the 20th century focused on sites that were easiest to build logistically. And in the 70 years since then, the sites that were originally bypassed have become more complicated to consider because of evolving water rights, cultural preservation and endangered species laws.

“The best dam sites have already been built,” said Rep. Jared Huffman, D-San Rafael, whose congressional district spans the North Coast. “And even a great big dam is not going to create more water when you've got watersheds that are pretty fully appropriated and already captured.”

He pointed to Marin County’s seven reservoirs, two of which aren’t typically tapped except in the extreme drought conditions like what were faced last year. Huffman also noted that Lake Sonoma has not gotten close to running out of water, but Lake Mendocino has had multiple years of running low of water.

An example of the water rights and environmental law complexities of even existing reservoirs is the current political and legal turmoil surrounding the decommissioning of the Potter Valley Project in Mendocino County.

That includes a hydroelectric station that diverted water from the Eel River into turbines that have emptied into the east fork of the Russian River, which backs up behind Coyote Dam to create Lake Mendocino. Fisheries groups signaled their intent to sue former plant operator Pacific Gas & Electric Co. to remove what they call migration impediments, namely that water diversion as well as dams that create two Eel reservoirs, including Lake Pillsbury in Lake County, according to The Press Democrat.

One answer to the North Coast water storage challenge is to get the most out of the existing reservoirs.

The U.S. Army Corps of Engineers, which built and manages the dams at lakes Sonoma and Mendocino, has wrapped a two-year pilot test of a drought-sensitive approach to flood management, one of the agency’s key peacetime tasks. The conventional approach in the rainy season is to follow a complex regimen that guides ramping outflows up and down to keep a certain portion of reservoir capacity empty so heavy rains don’t risk a dam breach or call for a large emergency release of water.

But a statewide team of water researchers since 2013 has been working on a concept called forecast informed reservoir operations, or FIRO.

“A lot more is known about atmospheric science than 60 or 70 years ago, and that allows us to carry more water behind the dam,” said Nick Malasavage, Ph.D., P.E., chief of the operations and readiness division at the San Francisco District of the Corps.

Testing of the methodology started at Lake Mendocino in 2019. Malasavage said it has been shown to manage heavy “atmospheric river” rains like what came in 2019 as well as retain water for two drought years. FIRO is estimated to allow 5%-20% more reservoir capacity to be retained, compared with the conventional method. Lake Mendocino roughly holds about a one-year supply of water, and Lake Sonoma about two to three years.

“When we talk about a multiyear drought, we want to use this approach to buy one more year,” Malasavage said. “There is a physical limit to how much we can hold onto for one more year. There’s no new construction to do that, so that’s why we’re pouncing on that opportunity right now.”

The Corps is now working to officially change the Coyote Dam water control manual to use FIRO, and a test is being planned for using the method at Lake Sonoma.

Just like Lake Mendocino came frightfully close to empty last fall, so did Marin County’s storage, according to Paul Sellier, director of operations for Marin Municipal Water District. Even after emergency drought measures, the reservoirs just before the October rains had fallen to 33% capacity, or 27,000 acre-feet, but only 17,000 acre-feet of that was realistically usable, he said. (An acre-foot is the amount of water that can cover 1 acre 1 foot deep.)

Though heavy rains in November and December have brought Marin’s reservoirs back up to about average capacity, the district is using a $2 million state grant to fund a strategic assessment of water resiliency options. Jacob Engineering is studying various options: a pipeline across the Richmond-San Rafael Bridge, desalination, more reservoir capacity, increased winter deliveries through the Sonoma Water pipeline and greater use of recycled water for outdoor irrigation. That study is set to be completed by August.

The county was considering the Richmond Bridge idea last year. During the 1976-1977 drought, pipeline was installed on the bridge, and today the cost estimate is around $100 million, Sellier said. As for desalination, options being considered are temporary and permanent units of varying output capacity (5 million to 15 million gallons per day), and use of 100% renewable energy through MCE Clean Energy for the power-hungry units. The cost of such units can be up to $220 million.

At Sonoma Water, a utility that supplies about 40 million gallons of largely Russian River water daily to over 600,000 residents in Sonoma and Marin counties, the focus is on ramping up storage by putting water underground.

The Public Policy Institute of California has estimated that though 50 million acre-feet of surface water reservoirs have been built in California, the storage potential in aquifers is enormous: from 1 billion to 3.5 billion acre-feet.

“Sonoma County groundwater basins don’t’ have the potential like in the Central Valley with hundreds of thousands of acre-feet they can bank,” said Carlos Diaz, a Sonoma Water principal engineer. “It’s not so much a savings account but a credit card, where you can take it out and put it in back in the following season.”

In Sonoma County, aquifers range from thousands of acre-feet to one in Sonoma Valley is 20,000 acre-feet available, according to Sonoma Water.

The agency is using a $6.9 million grant to get its two of its three Santa Rosa Plain drought-response wells ready to not only pull water out in dry months but also put it back in during wet months. The wells were installed during the 1970s drought and used during dry spells since, most recently in 2015. One was turned on last year, but the other two had to have upgrades to better treat the water.

And in northern Sonoma County’s Alexander Valley, Dry Creek Rancheria has received funds to build groundwater storage, with potential for distribution to surrounding farmers.

State Sen. Bill Dodd, D-Napa, whose district includes Napa, Solano and part of Sonoma counties, said North Bay residents, businesses and policymakers need to focus on resiliency of the water systems.

“There are supply and demand side improvements that could be made, from ground water recharge to changing the way we do our landscaping,” Dodd wrote in an email. “The state has supported the North Bay Water Reuse Authority which has been successful at doing purple pipe recycled water.”

State Sen. Mike McGuire, D-Healdsburg, who represents the North Coast, said the Legislature has made water infrastructure a priority in the last two years, appropriating billions for the effort, The 2021-2022 budget included $5.2 billion for water resilience projects across California. In the North Coast, there have been over $93 million in grants for water and drought infrastructure in the past six months alone, he said.

“Cities and counties in every corner of our region will be installing massive water storage tanks, building off-stream storage ponds, connecting playing fields to recycled water, rehabilitating wells, consolidating small water systems, and many other significant upgrades,” McGuire wrote in an email. “And more projects are on the way.”

Another storage approach in the North Coast is to allow more pond-size reservoirs to store winter rainwater. Wood wants to improve the process for rural property owners such as residents and farmers to seek permits for small reservoirs that would fill when rainfall is plentiful for use when it’s not.

“Agriculture is a big user of water, and being able to give opportunities to store water on site is important,” said Wood, the North Coast Assemblymember. “Hopefully, (off-stream reservoir permit applications) can be expedited, and frankly those are hard to get done.”

Two decades ago, a change in the state’s water rights regulatory approach to such on-site storage led to a backlog of thousands of permit applications in the North Coast.

In February of this year, Wood introduced Assembly Bill 2451, which would create a dedicated unit in the state Division of Water Rights for drought planning, response and resiliency, and it would start out focusing on North Coast watersheds. Wood likened the unit to the fire-prevention team that was made part of the state’s firefighting agency. AB 2451 was referred to the Assembly Committee on Water, Parks and Wildlife on March 3.

Jeff Quackenbush covers wine, construction and real estate. Before coming to the Business Journal in 1999, he wrote for Bay City News Service in San Francisco. Reach him at jquackenbush@busjrnl.com or 707-521-4256.