This Mercury-News report discusses what is (and isn't) happening to the dam. The dam itself is in good shape, but the main spillway (drain) was damaged, and had to be throttled back to about 1/3 its maximum flow to avoid its complete failure. The emergency spillway is basically a deliberate low spot where water can flow out if the level gets too high, something which has never happened until now. The emergency spillway's capacity was identified as a limitation years ago, but the money was not spent to upgrade it. The article states:
In denying the request, an engineer for the federal government wrote that "during a rare flood event, it is acceptable for the emergency spillway to sustain significant damage."
That "acceptable risk" has become reality.