North Coast breathing easier after recent rains, but reservoirs still historically low
Last week’s surprisingly generous storm and several smaller rain systems expected this week are allowing water managers, ranchers and farmers around the region to breathe a sigh of relief.
Abundant rainfall has raised creeks and rivers, filled some storage ponds and provided flexibility to shift to greater reliance on surface water for a spell, reducing the pressure to lean so heavily on groundwater wells in some places.
It also filled smaller storage ponds and has started a new greening of the landscape in pastures that had been grazed down to cracked earth long ago.
“We’re all just in awe,” said Healdsburg dairyman John Bucher. “It’s almost like you can watch it grow. It’s just crazy.”
It also means domestic consumers are using substantially less water for outdoor irrigation, reducing demand on the system, said Don Seymour, principal engineer with the Sonoma County Water Agency.
But while recent wet weather has allowed most folks to take a bit of a breather, it’s likely just that, however: a breather, a respite.
Long-term reserves, especially in Lake Mendocino, are still at abysmally low levels. A significant amount of rain is still needed to raise water levels enough to face next spring and summer with any confidence that there will be sufficient supplies to get through to the winter afterward.
“There’s a big hole to fill,” Seymour said.
Recent rains have added about 5,000 acre feet of storage to Lake Mendocino, arriving just a week or so before the lake would otherwise have matched its lowest level ever: 12,081 acre feet.
Instead, it rose from about 12,864 acre feet on Oct. 22 to 17,676 acre feet a week later.
The gain was about half the 10,000 acre feet that flowed into the reservoir in all of last winter. (An acre foot is equal to 325,851 gallons, or about the amount of water needed to flood most of a football field one foot deep. It would supply almost 3½ water-efficient California households for a year, according to the Water Education Foundation.)
But that remains the second-lowest level since the reservoir was completed in 1959, and it is still almost 100,000 acre feet below the spillway, meaning the amount of water in the lake could be multiplied 6½ times before the reservoir reaches capacity.
Lake Sonoma, a far larger reservoir, gained about 14,500 acre feet in additional reserves after the big storm, bringing total storage to about 120,000 acre feet by Thursday. But that was still less than half the lake’s 245,000-acre-foot capacity.
Seymour said that both reservoirs receive water from catchment areas close to the same size — 105 square miles in the case of Lake Mendocino and 130 square miles in the case of Lake Sonoma.
However, Lake Mendocino will be more challenged to make up ground after two years of critically low rainfall because it’s located in a watershed that simply isn’t blessed with the same amount of rainfall as Lake Sonoma.
Adding to Lake Mendocino’s woes is the shutdown of the Pacific Gas & Elecric hydroelectric plant in Potter Valley. Water from the Eel River is usually transferred through the plant to the Russian River and Lake Mendocino, but water diversions there are now about one-sixth what they normally would be.
“This great gift of rain like we got last weekend is not enough to dig us out of drought,” Nick Malasavage, chief of operations and readiness for the U.S. Army Corps of Engineers, San Francisco District, which operates the two reservoirs, said Friday. “We are still at historically low pools for this time of year.”
Any success the future might hold in augmenting existing storage remains, as always, in question, but particularly so this year. An intensifying La Niña season along the West Coast that means the Pacific Northwest likely will see more rain than usual this winter and the southwest, less, but uncertain prospects for the transition zone in and around the North Coast.
As for the immediate future, it’s likely to include more moisture than usual, however, with some rain on Monday and again on Wednesday, though likely a fraction of an inch in most inland areas.
The ground already is wet, so less will soak in before running into creeks and rivers, however, and more might be captured in reservoirs, water managers said.
These rains also demonstrate “a very active weather system” that bodes well for the immediate future, said David King, a meteorologist with the National Weather Service in Monterey.
