Seems like a poor design.
Inadequate. This is their "Fukushima" event, perhaps. A situation beyond the expected design.
I did a lot of building on the north side of Sacramento. The levees in that whole area of California are a joke to me. I spent most of my life in Kansas City along the Missouri and Kaw River. We learned what bad levees did in the 1951 flood and in the ‘93 flood.
California has neglected this just waiting for a disaster so that Federal money will come fix it.