Got it. I’m not thinking of arroyos in the flatlands.It's how all our reservoirs are in San Diego County. They're basically on seasonal creeks, or on creeks that are barely a trickle, or just some standing water, most of the year. They only flow during rain events Our reservoirs are basically retention basins and have no hydroelectric capability.
I’m talking about hills, and much larger reservoirs. Example: There is a small lake at the base of the Hetch Hetchy power generation tunnel. Pump water uphill into Hetch Hetchy as a way to store energy. Let it flow back down when you want electricity. It would use the pair of lakes as a giant battery.