I am modelling a diversion channel steady state 1D, so I have a main channel and a side channel connected by an upstream and downstream junction. When delineating my geometry, I drew a line of confluence between the two reaches, and butted up the cross sections from each side. The initial run did not allow flow to transfer between the two reaches, so I added a lateral structure at the terrain elevation and using a very low weir coefficient to represent overland flow. Headwater and tailwater connections are connecting appropriately, and the table results show flow over the lateral structure. However, RAS Mapper shows gaps between the two reaches and the water surface elevations do not line up (0.1 - 1 ft difference).
Without switching to unsteady or 2D, does anyone have any suggestions or thoughts?