Mapping Streams using USGS Topo map, best practices

USGS topographic maps are okay to use as a source (that type of US government publication is public domain).

In my semi-arid area I use the USGS maps (selected in the JOSM "imagery" pulldown) for three things when mapping waterways:

1. To see if the waterway is considered big enough to map (I also look at available aerial imagery). There are lots of dry gullies around here that may have a visible ephemeral water course that carries so little water so rarely that it is debatable if it counts or not. But if the USGS thought it counted then I figure that is an indication that OSM might be interested in it.

2. To see if the waterway has a name.

3. To roughly draw the waterway in.

I find that the USGS topo imagery layer in JOSM (which uses the older maps) to have a fair number of errors in location. So once I get the waterway drawn in per the USGS topos I then adjust it based on imagery to get a better location.