This article from the Wall Street Journal makes the case.
MORGAN HILL, Calif.—Two years ago, Uvas Reservoir here stood at just 2% of capacity—much of its lake bed baking in a merciless drought.
But now the half-square-mile reservoir is spilling over, sending so much water downstream that a recreational-vehicle park a few miles away in the brush-covered hills has closed because of the threat of its lone bridge being flooded out.
“It’s hard to complain about getting the water we need so desperately, but I wish we could just get it spread out more,” said Matt Gifford, a 30-year-old manager at a retail store, who was fishing at the lake on Wednesday. His nearby home is threatened by flooding from another reservoir.
With more rains having drenched the state over the past several days, California’s overburdened dam system faced a new stress test after a near disaster at Lake Oroville earlier this month raised questions about the health of the state’s extensive network of reservoirs.
State officials on Feb. 12 warned of an impending collapse of an emergency spillway at Oroville as they attempted to lower the lake’s level following weeks of rain and snow.
The situation has since stabilized as nearly 200,000 evacuated residents were allowed to return to their homes and crews helped fortify an eroded area of the spillway.
But new flooding concerns surfaced, including at California’s largest reservoir, Lake Shasta, which on Feb. 12 began releasing water from its spillway for the first time since 2011.
With water shooting out of the release valve, the swollen Sacramento River downstream experienced flooding, including of a golf driving range, a sheriff’s office parking lot and some riverfront homes.
Officials of the U.S. Bureau of Reclamation, which operates the 47-square-mile lake, said they have to make room for more rain and snow this winter to avoid wider flooding.
“The flooding would be so much worse if our facility wasn’t there,” said Sheri Harral, a bureau spokeswoman at the lake, in the foothills of the Cascade Mountains.
Further south along the Sierra Nevada, dam releases from Don Pedro Reservoir prompted the Turlock Irrigation District on Thursday to warn farmers and ranchers to move property and livestock to higher ground as the Tuolumne River threatened to surge out of its banks with the approaching storms.
Widespread flooding unrelated to dams has been reported in the state from the fresh round of storms. In Southern California, at least two people died in floodwaters and dozens of others were temporarily trapped in their vehicles, while in Northern California, residents of the small farming town of Maxwell were evacuated because of high waters.
The flooding is happening as a devastating, nearly six-year drought has finally ended in much of California. However, the semiarid state is never far from drought, and because of limited storage facilities is unable to recover much of the water being spilled when reservoirs like Uvas reach 100% capacity.
Proposed new reservoirs to capture storm runoff have been blocked by environmental groups and other opponents for decades, in a situation that frustrates water managers.
This year “is a textbook example of why we need more storage in California,” said Timothy Quinn, executive director of the Association of California Water Agencies.