[GRASS-user] stream network

[Michel Wortmann]

HI Janet,
can you specify what you mean by 'fully connected stream network'? 
'connected' doesnt mean much on a raster map or did you convert it a vector?
I would try to build your stream network from the accumulation raster 
map by thresholding it with a certain catchment size (in cells). Eg.
r.mapcalc exp='streams=if(accumulation>1000, 1, null())'
That way you see what is happening in the accumulation map as a result 
of the DEM.
Best,
Michel

On 03/02/2016 08:42 PM, Janet Choate wrote:
> Hi Will,
> When running r.watershed on a small 35 hectare watershed, it produces 
> a fully connected stream network. However, when running r.watershed on 
> a 6400 hectare watershed, the stream network is not fully connected.
> No preprocessing with regards to merging different raster maps, 
> however, I did try using r.fill.dir first to deal with any possible 
> depressions that might be causing non-connected stream segments.
> thanks,
> Janet
>
> On Wed, Mar 2, 2016 at 11:22 AM, Will Fields 
> <will.openfields at gmail.com <mailto:will.openfields at gmail.com>> wrote:
>
>     Hi Janet,
>
>     Can you give some more information about what you mean by larger
>     watershed basins?  Did you do any preprocessing of the elevation
>     raster before you tried to extract the stream networks?  Were you
>     using an elevation raster that had been merged from different
>     rasters?  I've ran into issues in the past where "seams" along the
>     original edges of a raster resulted in odd stream networks.
>
>     Will
>
>     On Wed, Mar 2, 2016 at 11:40 AM, Janet Choate <jsc.eco at gmail.com
>     <mailto:jsc.eco at gmail.com>> wrote:
>
>         Hi GRASS community,
>         When creating a stream network with r.watershed, I end up with
>         some isolated stream segments - particularly in larger
>         watershed basins. Does anyone know how to generate a stream
>         network that is fully connected, or how to correct this issue?
>         thank you,
>         Janet
>
>
>
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