Complex sentence: Because the spillway is a separate structure from the dam, there was no danger of the main embankment being breached, and evacuation of Oroville itself was not being considered as there was no threat to public safety.
Split into simpler sentences: Because the spillway is a separate structure from the dam, there wasn't any real danger of the main embankment being breached. The dam's structure itself continued holding and no damage was found, and the possible evacuation of Oroville itself was not being considered as there was no threat to public safety.