I suppose then I do not fully understand how rivers function.

The way I envisioned it, the river flows out of Lake Orpheus (perhaps from a glacier), flowing from a higher point (up in the Ironside Hills) to the lower points of the coastal plains. Other then that I thought major rivers split all the time? I suppose I just don't understand the exact geographical reason, though my model here was the Rhone.

Thank you for all your comments, I'm still plugging away.

And thank you to Ghostman for pointing out my ghastly inaccurate steppe symbols.