Stream junction modeling

[crode]

I am working on a model which includes a junction of 2 streams, roadway, 2 bridges and a floodplain all within very close proximity to one another. I have a good idea on what is physically happening at the site from talking with numerous people within the community however, am having a difficult time trying to model it in Hec Ras. I have started by modeling the bridges and junction as described in the Hec Ras documentation. The 2 streams are quite different from one another with one being relatively steep with no floodplains and the other has relatively minimal grade and a wide floodplain. The issue i am having is with the stream with the minimal slope and wide floodplains. What happens is during peak flow events being modeled, the water expands to flow in the floodplain area and even surrounds the bridge and overtops the road. In the model the way i have it set up based on the location of the confluence, the water from this stream becomes "funneled" as the cross sections become much narrower. Should i be thinking about moving the beginning of the confluene or juction upstream more to contain the floodplain area? If so, this would put the bridge and roadway in the junction area. How would these features now be modeled? Any ideas or suggestions are welcome and appreciated. I have included a plan of the area with this post which may help.