Water spills over top of dam
‘A powerful smash of water’ triggers cascade; more rain to come
MORGAN HILL — Anderson Reservoir reached maximum capacity early Saturday morning and began spilling over for the first time since 2006, the latest sign of this year’s enormously wet winter.
Normally that would be a cause for celebration after years of devastating drought. But the development is worrisome because state and federal regulators have directed the Santa Clara Valley Water District to cap storage at 68 percent, or 61,810 acrefeet of water, to avoid a catastrophic flood in the event a major earthquake causes Anderson’s dam to fail.
District officials, though, say the chances of that happening are extremely low.
This year’s winter is one of the wettest in 20 years. And the rain keeps coming. A powerful storm on Friday bludgeoned the Bay Area, and more rain is expected to fall throughout the holiday weekend.
“We expect it to rise a little bit more today, and with the storms on Sunday and Monday it will rise pretty significantly,” Marty Grimes, a spokesman for the water district, said Saturday morning. “That’s where we have some concern that it could be enough to cause some
flooding issues on Coyote Creek.”
On Saturday, several hundred people flocked to the dam to watch water cascade from the reservoir.
Steve Lane, a 30-year Morgan Hill resident, said he lives right above the lake and he’s been monitoring the water levels to see when the reservoir would overflow.
“The waterfall is exciting. It’s massive. It flows over a 70-foot drop almost straight down a cliff of jagged rocks,” Lane said. “When it’s overflowing, it’s a powerful smash of water that sprays mist on the people who are on the side of the cliff watching it.”
Lane said that he’s seen the reservoir overflow several times in the past, but to him “it’s new and exciting every time.”
The 59-year-old said he’s been stocking up on supplies like food and water for the storm, but since he lives above the lake he’s not too concerned about flooding at his home.
“I have friends who live right below the dam, and it’s scary for them,” he said. “If it was flooding enough, it could affect my ability to get in and out of the house down in the valley. I don’t foresee that, but it’s possible.”
An outlet at the base of the dam has been fully open since Jan. 9, releasing water into Coyote Creek at a rate of more than 400 cubic feet per second. It could take a month or more for levels to drop to the two-thirds mark, according to the water district.
Water officials look at the time of the year, anticipated rainfall and other factors to decide when to start releasing water from the dam, but the amount of water being released wasn’t enough to keep up with the downpour of rain on Friday.
“You don’t release your water prematurely,” Grimes said. “Given that it’s primarily a water supply reservoir, we certainly want to hold onto the water that we can.”
Technical staff on Saturday came to take a look at the dam, and everything is working as intended, Grimes said.
The cap, which has been in place since 2009, won’t be lifted until the water district finishes rebuilding the dam.
Construction on the $400 million project is scheduled to begin in 2020 and end by 2024.
It would take a magnitude 7.25 or higher earthquake striking within about 1.2 miles of the dam to cause damage, according to the water district. Even then, the water district rates the chances of an immediate failure of the dam as “exceedingly remote.”
On its website, the water district said, “Keep in mind that this is the same dam that has performed well in numerous earthquakes, including the 1989 Loma Prieta earthquake, since it was built in 1950.”