This is a pretty interesting video on how natural water storage works. If you imagine the CA central valley as one big pond before we drained it and the aquifer beneath it, it's obvious that there is no solution to CA's ag and water problems without fixing it.
Siphoning off the yearly runoff towards the Delta is just going to worsen the subsidence and increase the desertification upstream of the Delta which will worsen the Delta salinity and water levels. There's an analogous problem in the Eastern Sierra in NV.
I bet we're going to handle this problem the way we're handling the fire problem - with inaction.