[GRASS-user] Re: r.stream.extract with external flow accumulation maps

[Mark Seibel]

> I believe that the flow accumulation grid was produced using ArcHydro. I put
> the link to the data set that I am using below if anyone wants to try it
> out.

Hi.  Not sure if this is the issue, but I recall this from the manual.

"
accumulation
Input map, optional: Accumulation values of the provided accumulation
map are used and not calculated from the input elevation map. If
accumulation is given, elevation must be exactly the same map used to
calculate accumulation. If accumulation was calculated with
r.terraflow, the filled elevation output of r.terraflow must be used.
Further on, the current region's resolution should be identical to the
accumulation map. Flow direction is first calculated from elevation
and then adjusted to accumulation. It is not necessary to provide
accumulation as the number of cells, it can also be (adjusted) total
contributing area in square meters or any other unit.
"

Mark