This is the accessible boarding spot for Kali River Rapids. Follow the instructions in the Guidebook for Guests with Disabilities or the CM at the entrance to the queue for where to go.
As an empty boat goes by, the CM opens the gate (the bar going across the water in the middle of the picture). That traps a boat so that it will not move until all the guests have boarded.
For exiting, the CMs do the same thing.
It is not an easy transfer. A wheelchair can be parked next to the boat, but you have to go down into the boat and then over to a seat. The seats are made of plastic and the seats and floors can be wet and slippery because of water coming into the boat. Once you have gotten into the boat, the CM will move your wheelchair out of the way. You will return to the same dock when your ride is over.