Sonoma Valley water agencies hope for rain amid lowest water levels at reservoirs

The rain pelting Sonoma Valley this week could not be more needed, just as a local reservoir marked its lowest water level since its inception, despite increased conservation efforts by the public.

Lake Sonoma, the reservoir most responsible for Sonoma Valley’s water flow, reached its lowest point since it was constructed in 1984 at just 40% capacity as of Nov. 27 — down from the historical average of 73.3% recorded from 2013-21. The drought’s impact on Sonoma Valley watersheds have challenged people and animals alike, according to experts.

“We're still in the third year, going into a fourth year, of drought depending on what happens going in to 2023. There’s a lot of uncertainty,” said Don Seymour, deputy chief engineer for water resources planning at Sonoma Water.

While Sonoma Water customers at the county level have cut back their water usage by approximately 30% from their 2018-20 average levels, city of Sonoma water users have consistently failed to meet the mandatory 20% reduction goal.

From July 2021 through June 2022, city water customers reduced their water use by 15.3%, said Brad Sherwood, assistant general manager for Sonoma Water. The “good news,” he added, is the city customers reduced their water use by 17% in October 2022 compared to the same time in 2020.

For comparison, Valley of the Moon Water District users have reduced their water usage by 24%, according to administration manager Amanda Hudson with the district.

The city of Sonoma previously met its conservation goals, but took steps backward earlier this year. Sonoma Ecology Center Senior Scientist Steven Lee believes the public is losing focus on the drought.

“There's fatigue from it, right?” Lee said. “We have to continue to be diligent about water use efficiency and conserving the resource at the same time... we have an upcoming wet season ahead of us, and we have to be patient to see where we end up.”

Water use amid the ongoing drought has added stress on Sonoma’s reservoirs, causing residents of Sonoma Valley to sap up groundwater to supplement their regular water usage. As a result, Sonoma Water is engineering projects to monitor the ongoing use of groundwater in the region.

But the persistence of drought is steadfast. Sonoma Valley will require a significant rainy season to overcome the past three years of unfavorable rain totals.

“We’re hoping for a more normal, wetter year for recharging the groundwater systems and our reservoirs,” Seymour added. “It's just too early to tell.”

Despite efforts to conserve, the state of water in Sonoma Valley remains precarious and it is unclear when drought restrictions might end, Seymour said. If the mega-drought continues in 2023, he said, those restrictions could become more severe.

Water uncertainty extends beyond people, however.

The drying of Sonoma Creek in 2021 was one of the first major ecological systems impacted by prolonged drought, Lee said, and it was the first time “in local memory” the creek bed ran dry.

Disruptions to the flow of the creek can have major impacts on wildlife and their reproductive cycles, Lee said. After stretches of the creek turned into pools where freshwater shrimp could accumulate, some of those pools dried up, causing the species sheltering in them perished, too.

“It's not like the shrimp can swim upstream to find a wetter place like some of the fish can,” Lee said. “So we definitely know it is harmful and difficult for the species and there's stress on the species when you have really dry years.”

But during significant rain events – for example, the atmospheric river of October 2021 when parts of the North Bay received about half of its annual rainfall for the region in 24 hours – there’s potential for regeneration. Lee said that October downpour enabled Chinook salmon to swim up Sonoma Creek and reproduce for the first time in since 2016.

“We haven't seen that yet this year,” Lee said.

Steelhead trout also capitalized on the historic rainfall to swim up Sonoma Creek last year, but there’s one major difference between the reproductive cycles of the two species, Lee said.

While Chinook spawn will spend one dry season in the creeks where they’re born, Steelhead offspring spend two years maturing before they travel out to the ocean.

Because of Steelheads’ extended time in freshwater springs, Lee said they are an “indicator species” for watershed health.

“When you’re hit with multiple year droughts and you have multiple years where there's... really terrible dry, warm and low flow conditions, that can be really stressful on the steelhead,” Lee said. “Because they don't have to just make it through one dry year, they have to make it through two dry years.”

Lee said the recent storm system which brought more than 2 inches of rain to Sonoma Valley could help adolescent Steelhead to travel back into San Pablo Bay.

Of course, the volume of rainfall during the coming winter months will be key to determining if drought restrictions remain in place for Valley of the Moon Water District users, Hudson said.

“Conserving over previous winters can be challenging as it is already a low-usage time,” Hudson said. “This rainy season will determine if further conservation will be required in the spring.”

In June, Index-Tribune reported on the declining groundwater in Sonoma Valley’s aquifer after decades of unregulated use, according to Sonoma Valley Groundwater Sustainability Agency. Just over half of the water used in Sonoma Valley comes from the ground.

Sonoma’s water agencies are beginning to implement projects to make the most of rain that does fall, using it to refill reservoirs and replenish Sonoma Valley’s water basin.

“This year the district was successful in a grant application for nearly $3 million in Drought Relief Project Funds from the California Department of Water Resources for two aquifer storage and recovery wells,” Hudson said.

Whether Sonoma Valley enters another year of extreme drought conditions is yet to be determined, but in the meantime residents are still urged to keep up the fight to conserve water.

“Unfortunately, we don't have a crystal ball to say where we're going to be next May” Seymour said. “Are we going to be in a similar situation, or are we going to experience some really large storm events through the winter and and see a lot of recovery?”

Contact Chase Hunter at chase.hunter@sonomanews.com and follow @Chase_HunterB on Twitter.