Good stuff.
How do you figure out what needs to be done with the spillway facing south and getting hammered by the sun during the day and the cold nights in that area.
What impact does tons of cold water barely over freezing have on those stress areas when it flows over them?
With highways, joint maintenance is vital. Concrete expands about 2/3” per 100’ with a 100 degree temperature change. Highway blowups (we’ve all seen them) are caused by rocks and dirt infiltrating the joints and preventing expansion.
What I’ve seen the highway crews do is remove the old sealant, clean out the joint with compressed air, then reseal.
With temperature changes, concrete IS GOING TO MOVE. The laws of physics cannot be repealed here. You have to design for that eventuality, and make sure your design is kept up to spec.
The spillway is sited on two very different types of rock, one much softer than the other. Perhaps their thermal properties differed and produced stresses on the spillway.