Since the resolution of the planet isn't going to be such that rivers can form easily, instead the current model for erosion is good enough, more testing should be done along with possible visualization of dissolved sediments and sediments that are being transported.
Hydrosphere needs at least two layers for convection to happen, salt and fresh water help drive this system.
Hydrosphere will erode and deposit sediments and move water, may be best to implement water movement in the Geosphere to this system instead.
Hydrosphere needs a temperature for both layers. Motion of air currents drive surface water creating currents.
Since the resolution of the planet isn't going to be such that rivers can form easily, instead the current model for erosion is good enough, more testing should be done along with possible visualization of dissolved sediments and sediments that are being transported.