I am trying to generate a catchment area polygon from a digital elevation model. I am using SAGA tools in QGIS and used the Flow Accumulation (Flow Tracing) tool to generate a catchment area raster that clearly shows all of the channels (See image)
From here, how could I generate a catchment boundary polygon of the main catchment (middle of the raster)? Is there a tool in SAGA that could do this?
I am new user of QGIS and do not have technical expertise of GIS.