Is the area under the bridge accessible to wheel chairs with out having to use the stairs?

Yes it is

Yes

Yes... Ramps everywhere

There is handicap parking down at the water level so I think it should all be accessible without stairs.

I do not recall wheelchair accessibility. I don't think they have any.

Yes, the hotel has a ramp to get all the way down there and a little restaurants, or if you go to the park across, the other side of the river this park goes right next to the river so you can walk over there if you want too