Lower Crystal Springs Dam after the 1906 Quake
It was built to last. The 1888 Lower Crystal Springs Dam, situated next to the San Andreas Fault, survived two major earthquakes—the great earthquake of 1906 and the Loma Prieta in 1989—with no damage. A critical recent upgrade plus our vigilant 24/7 operation ensure that the historic 175-foot-high dam is able to safely contain Crystal Springs Reservoir drinking water even in a year of record rainfall.
The main upgrade under the Water System Improvement Program was the widening of the spillway—an emergency device for the safe release of water during heavy rains—on top of the dam. The new expanse gives us the ability to release 2.5 times more water than before—if necessary. But again, a spillway is an emergency feature---and one that we haven’t had to use for decades, according to SFPUC Local-Regional Water System Manager David Briggs.
The real safeguard is the day-to-day monitoring, anticipating and adjusting by our system operators. They open valves to release controlled amounts of water into San Mateo Creek, and divert water northward to San Andreas Reservoir (at left), on to the Harry Tracy Water Treatment Plant (below), and then to customers. They continually forecast the anticipated amount of rain and runoff into the reservoir and assess that inflow’s impacts on reservoir level. As needed, our operators will release controlled amounts of water from the dam—but always taking into account the timing of high tides coming up the creek from the bay.
We’ve been releasing water from the reservoir this way all winter, and have not come close to spilling water over the dam.
The San Mateo Daily Journal talked with Briggs a couple of weeks ago. You can read more on what he had to say about the safety of historic Crystal Springs Dam and our regulation of the water system here.