If the water is coming through the earthen dam from the reservoir, I would think it is an unfixable problem without draining the swamp so to speak (maybe in more ways than one). It would seem to me that once water found its way into the interior of the earthen dam the gig is up. I know water inside of things can go every which way but loose.
I would think that the swamp would need to be completely drained so they could either do some major repair of the earthen dam or the build a new one.
Is there a better alternative to a dam made of earth when the dam is this massive size?
What other alternatives? A series of smaller dams?
Oroville dam designers included "overdesign" in the thickness, depth, and dimensions of the layers of the earthfill embankment design. Thus there is a built in safety factor. All earthfill embankment designs have seepage. They just need to be on top of anything that develops.
The problem that I have is that there is an inaction behavior that seems to be ignoring the Dam Inspectors recommendations (inferring from multiple Inspection reports).