policy is to leave the dams open so they don't get crazy flash floods in the streets of Los Angeles. In the early 70s there was a drought like is happening now, probably a bit worse, and this same kind of storm came through and they decided to close everything to refill reservoirs. The streets of south LA flooded like crazy, about 40 people died. They've built up the LA river drainage system a bit better since then though and they can divert the flooding somewhat