I'm not sure whats going on with these guys. Do you know if they're digging that materiel on the barge out of the bank or are they dropping it in the river with that clam shell digger? It looks like some kind of grout mix to me and not muddy river bottom soup? Could be some kind of erosion control going out there?. Go ask em if they'd hire ya to be a run a round purchasing and fetching needed merchandise and spare parts you can find at the nearest location. I did a lot of that as a buyer for an mining equipment company in Sacramento and for a blasting company here in Colorado years ago. I'd be running to hose shops, NAPA and all kinds of suppliers all the time to keep things moving. I looked into the name on the side of the barge thinking that was the contractor... POSEIDON is a builder of specialty barges. Interesting looking company. Barges, Portable, Marine, Sectional, Dredge, Pontoon and Crane Barges for Sale ? Poseidon Barge Corp.
I would think maybe dredging out the high spots of sediment from the river bottom. If sediment continues collecting in certain spots, the spots will grow and grow until eventually they start to cause problems.
On the other hand, if they're trying to get the water level down by making more room, then those guys definitely have job security!