how to merge rivers?

[Arnaud]

Hello

I would like to simplify an existing Hec-Ras geometry by removing a reach and the associated junction.
There are two rivers in my geometry file (for the sake of the demonstration, say they are called "main", with 2 reaches called "upstream" and "downstream", and "tributary", with a unique reach).

Unfortunately the reach I want to delete is the "upstream" reach of the river "main", and therefore I want to merge two rivers together.

I first deleted the "upstream" reach of the river "main". When I then tried to delete the junction, Hec-Ras told me that "the river stations in the downstream reach need to be below the river stations in the upstream reach".

Obviously, because the two reaches belonged to two different rivers, stationing along the "tributary" river starts from 0 at the junction, which means the X-section downstream of the junction has a bigger station number than the X-section upstream of the junction.

I thought that Hec-ras would accomodate this and automatically re-number the stations but this is not the case.

Can somebody help me?

Thanks a lot

Arnaud