That’s a LOT of debris. Essentially, that’s the rock and concrete that the river cut away. I suspect that there’s some silt there, but a lot of it went downstream.
Here’s the Chickamauga Dam, which is near where I live. I’ve been inside a few times (since I work for the entity that operates it). It’s older, built around 1940, but it’s a tried-and-true design. There are 3 or 4 dams of very similar design along the Tennessee River including Watts Bar and Nickajack.
https://en.wikipedia.org/wiki/Chickamauga_Dam
I guess we will see in a day or so where they decided
to dump 1/2 million cubic yards of dredged material.