Streamflow modified by a dam

I'm trying to model a watershed that had a natural outlet at the east of it. For the hydroelectricity purpose, they build a dam that changed the streamflow direction of the rivers and now, the outlet/turbine is at the west of the watershed.

In ArcGIS/SWAT, I'm trying to reproduce these changes, but I don't know how to do it. Is it possible to import the dam properties and ArcGIS will simulate the new streamflow directions? Should I change the streams properties manually (.dbf/.txt :FROM_NODE and TO_NODE) without buging ArcGIS (The DEM and the streamflow directions won't fit)? If not, how should I do it?

Thanks in advance!