I'm no dam expert (pun intended) but if the water is on the left side of the dam, and that 'movement' is on the right side, or far side from the water, then it would seem to me the load of the water has pushed almost all the way through the dam itself which would be a bad scenario.

In the best case, that 'movement' would be from maybe not sloping the downstream side of the dam gradually enough.

Again, I'm no expert on this stuff.

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."