On 19/04/2012 01:48, Rich Shepard wrote:

  The attached pdf shows the basin map output by r.watershed based on a 10m
DEM and a threshold of 150000. The NHD level 6 subbasins are outlined in
black and the 1:24K NHD streams are in blue.

  The small white areas at the bottom left and center right appear to be
external to defined sub-basins. But I don't know how to interpret the larger
white areas with streams in them (center and top). The top margin is an
international boundary so I can understand not being able to completely
define sub-basins across that boundary since the DEM doesn't reach that far
north, but it's not consistently white.

Using the 10m DEM (I suppose your regions settings are the same?) then each pixel is 100 sq.m. So a threshold of 150000 would delineate watersheds of a minimum 15,000,000 sqm = 15 sq km. Does that seem to be what you're getting? If so, then white areas are small catchments that are hydrologically separated from the larger basins, and thus don't "belong" to any of the NHD larger basins. The streams in those smaller catchments flow off the map into some other large basin that doesn't appear in the NHD group.

I'm not sure if this helps any. What do you see as a problem?

  Please help me interpret the white areas with vector streams.

TIA,

Rich
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