In this instance I have come across a better image than I used before.
As can be seen the "lordly" figure is seated in the middle of a curling "aqueduct" which wraps itself around the river bank. One comment I read called the undressed figure a "water spirit". Though to me it seems like it might also have links to the Orontes figure that appears underfoot in the classic Tyche representation. Maybe the "aqueduct" is also not what it appears and might well be the supposed arcades along the riverbank that supported/adorned the Imperial Palace.