Nice.
So the emergency overflow is rated at 440,000 cfs with a maximum of 16 feet of water flowing over it.
One detail missing below the bottom of the bottom diagram is cross section D-D. It shows a cross section of the emergency overflow. The overflow structure extends below the level of the reservoir bottom, and has a lip extending down to resist the outward water pressure. There is only a short concrete lip at the bottom of the outflow surface and no deep construction below the exposed face.
That Ogee is not going anywhere, concrete doesn't float. In fact, water is 62.4 #/cf, and concrete is 150 #/cf, so there are simply no buoyancy effects that would negate the forces of water flow over the top; in fact the opposite, overburden and dynamic effects of the water above the weir would probably improve the reliability, although it has been a long time since I designed one of these. Given the flow characteristics of large bodies of water, there is no backside turbulent flow, impact of debris is a nominal force and water is simply very predictable because it has no shear strength above freezing.
It's a straightline slope from peak, which matches the pressure curve on the lakeside.
The lakeside is keyed into bedrock- this section may be to to scale, but it is easily misinterpreted by the layman- we do not have the specs, which were probably determined by the rock type and design code at the time. That weir is 3 stories tall and weighs at least 70,000 pounds per foot of linear length. In other words, that's over 4 concrete trucks full of concrete per foot (don't forget the key!).
So the real threat is scour and fracture of the bedrock that it is keyed into. With 70 kips per foot gravity weight and a 30 foot deep lateral section, the bending strength of the weir should be more than adequate to resist fracture, even if there is a breach of the bedrock.
The fact that they are working overtime to put boulders, cobbles and concrete on the backside to protect it while they are releasing 100,000 cfps tells me that they know exactly what they are doing, and they know a lot more about the situation than they did 4 or 5 days ago.
The overburden has been removed by the usage of the emergency weir, so they can see the supporting bedrock and actually build on it (thank you scour! Work smart- let the water do the work for you!), the emergency weir has been tested and proven (again- there are no impact loads or anything other than normal dam building stuff- as long as the foundation isn't compromised, the weir will do just fine), and the scour rates on the spillway are acceptable enough to run it almost full tilt to buy them some time.
Let the engineers do their job, they have handled it exceptionally well so far.