[GRASS-user] r.stream.extract

[Markus Metz]

M S wrote:
> [...] I'm looking for suggestions to tune the stream
> extraction for flat areas with relatively low relief.  Additionally,
> the component of many wetlands.
>
> My first question is about the accumulation parameter.  As I
> understand it, MFD is only available in GRASS 7 with r.watershed.
r.watershed with MFD is also available in grass65.
>   I'm
> on 6.4RC5.  If I dont input accumulation with my elevation, will MFD
> be used in r.stream.extract?
>   
Yes.
> Looking at the weight parameter, it seems this may help tune the
> results also.  For the project area, I have coded land use where I can
> essentially input wet areas (water bodies & wetlands), and all else as
> dry (uplands).  Would this help provide more accurate results, or is
> there another intended use of this parameter?
>   
Yes, that should work. You can save some memory when using r.mapcalc 
first to apply the weight to the accumulation raster, then feed the 
weighed accumulation raster to r.stream.extract
> For the mexp parameter, it seems to be applicable to helping with
> results in flat areas such as this study area.  Is there caution
> against using a higher mexp value if one's whole project area is
> relatively flat?
>   
In theory, you could end up with no streams at all if mexp is set too 
high, because larger mexp values decrease the number of streams in flat 
areas.

Hope that helps,

Markus M