It's easiest to run r.watershed interactively. The basin map output by r.watershed identifies each basin by an even integer ID value. Create a hill-shaded version of your basin map by compositing it with the aspect map using d.his . Try a 3D drape of this. The accumulation map calculates the number of cells draining through each cell.
Negative values indicate the cell receives some off-map flow also.
When you d.rast this map, it shows the White Clay Creek, Christina River and Elk Creek channels, but not much else. Create a vector layer of inferred streams. First, use r.thin to thin the binary raster streams map to 1-pixel thickness. Then use r.line to vectorize the streams. Then run v.support to build the topology for this stream map.