Santa Margarita Lake spills over
Our two San Luis Obispo County supervisors from the North County visited Washington, D.C., this week seeking federal money for county projects. One project would almost double the capacity of the Salinas Reservoir, also known as Santa Margarita Lake. I hope, however, that our supervisors aren’t also considering piping our Salinas River water out of our Salinas River Valley.
The two county supervisors are John Peschong of Templeton and Debbie Arnold of Pozo. They represent two large, inland districts. Peschong’s 1st District is most of the northern part of the county. Arnold’s 5th District is just south of Peschong’s. Both extend to the county’s eastern border.
Santa Margarita Lake can now hold about 24,000 acre-feet of water. The supervisors’ proposal would almost double that storage capacity to a total of 45,000 acre-feet. An acre-foot of water is about what you’d need to cover a football field with water 1 foot deep.
But two questions should be answered before we spend millions of dollars altering the Santa Margarita Lake dam to hold another 21,000 acre-feet. Question No. 1: Can that 75-year-old dam safely hold that much water? Question No. 2: Who’s going to be able to use that added water?
That safety question is vital. The dam was built in a rush in preparation for World War II. Its water was to go to Camp San Luis Obispo. The construction contract was signed May 21, 1941. The dam was designed by two moonlighting engineers who had day jobs with the Los Angeles Flood Control District.
And they still hadn’t finished designing the dam when the contractors started building it. That concrete dam was deemed fully constructed in January 1942. But there were leaks, especially where the dam’s left abutment meets the sandstone canyon walls.
Army engineers decided it wouldn’t be safe to install the planned steel spillway gate in the dam. So the mouth of the 19-foot deep spillway at the top of the dam remains open today. That’s why the dam can now hold only about 24,000 acre-feet of water instead of the 46,000 it was designed for.
Engineers were able to stop most of the dam’s leakage by pumping concrete grout into the rock formation. It still leaks a little. An engineer told me most dams do. But will this dam still be safe if it has to hold back almost twice as much water as it does now? You tell me.
Now, what about fairness? If the dam’s safety could be guaranteed, would it be fair to pump the added 21,000 acre-feet of water southward over the Cuesta Grade, out of the Salinas River Valley and away from North County? I don’t think so. It might be fair, however, to collect 21,000 acre-feet of added water behind the dam if that water stays in the North County. The North County needs more water.
We now have more irrigated vineyards and orchards than anyone dreamed of back in 1941. We’re concerned because extensive irrigation pumping has radically lowered some of our groundwater levels. To me it seems fair and proper to offset that groundwater loss with Salinas Dam water.