"Tubes along the river right next to a water inlet and/or outlet, are they for measuring water level or something?"
A: "It’s the stem that rises and lowers as the gate goes up and down. They work like a screw with a handle or motor operator. These appear to be fully open. I worked in water/waste water 20 yrs."
Yeah, that "special" finger !
. The balls are added to help in grinding the ore.