I have a question, after you create the junction, the river is divided, whereas that the junction was made between station 1 and 2, how do I create a culvert between station 3 and 0, Since the section is divided?
There’s too much to include in a reply here. Try reading through the manuals where they discuss lateral structures. Also search on “lateral structures” in The RAS Solution. There are a number of posts that discuss this topic.